Amateur Radio Pages on MDS975
MDS975 Home Page
My Home Page

Amateur Radio Button
My Station button
Antennas button
Accessories button
Projects button
Data Modes button
Information button
Portable Operating - /P -  button
QSL button
RSGB button
Links button
QRM - Home Plug Networking Interference and other QRM
Contact button

Mini Site Map

MDS975 Home

Feedback



QRM from BT HomePlug and

BT Vision PLT
adapters






G Whip Antenna Products
Get on the air with
TOP QUALITY
BRITISH
G-WHIP
ANTENNAS





Site Search

powered by FreeFind
M0MTJ  |  Operating Conditions  |  Antennas / Aerials  |  /P Portable Operating  |  Accessories  |  Projects & Kits  | Useful Information
Contact MØMTJ   |   Contact M6ORS   |   Links to Amateur Radio Sites   |   RSGB   |  QSL  |   The Amateur Radio Mini Site Map


On This Page:
FT Meter   |   ALC Power Adjustment and Dummy Load for QRP op's   |   Field Strength Meter
Using a Dynamic Microphone with the Kenwood TS-590 home-brew DIY Cable Adapter
More About Microphones   |  Microphone Pre-amplifier Ideas   |   Icom HM-103 Microphone Mod's
Microphone Wiring  |  Morse Code Practice Oscillator  |  Shortened Top Band Antenna  |  Balun and UnUn Ideas
  (External Link): Antenna project - Dual band vhf / uhf dipole antenna

More pages:
DC Distribution Box with Reverse Voltage, Over Voltage and Transient Protection
   Speech Processor  |  Mic Preamps  |  Palstar PS-30
High Efficiency Extension Loudspeaker  |  Hands Free Mobile Microphone for FT-7900 etc
A PTT Switch for a communications headset by Ian MØIAT
An FT Meter by Ian MØIAT

DC Distribution Box with Reverse Voltage, Over Voltage and Transient Protection
DC Distribution Box with Reverse Voltage, Over Voltage and Transient Protection

“Anyone who has never made a mistake has never tried anything new.” - Albert Einstein



RADIO PROJECTS & KITS

One of the really fun aspects of amateur radio is making things for yourself and I like nothing better than making things, be they small circuits of kits or going outdoors with some antenna wire.

Probably the best and most important DIY project for any amateur radio station is building an antenna of some kind. This is often a wire antenna for use on the HF bands such as an Inverted V, Inverted L, Dipole or Doublet Quad Loop or Windom etc. For the shorter wavelength VHF and UHF bands it's more practical to construct more complex antennas such as a single band Slim Jim or Yagis; I've had a go at a few such projects.

Other projects will be an electronic unit of some kind: For the Intermediate Level licence it is necessary to make several practical electrical and electronic circuits and also build a complete and useful device related to the subject of amateur radio. I chose to make a Morse Code Practice Oscillator; this project can be seen a little bit further down this page here.  I have also built a Field Strength Meter - "FSM" also shown further down this page here.

In January 2012 I set about making a microphone adapter cable to connect a dynamic 'stick' microphone and a separate PTT hand or foot switch to the Kenwood TS-590s transceiver. This, of course, led to looking at the transmitted audio quality and the subsequent filtering and DSP adjustments which has all been very useful and interesting. Read more here.


Due to being unable operate from March 2010 with all my equipment being packed away for a house move that had been constantly delayed and finally fell through, I began thinking about a few more ideas for homebrew (d.i.y.) projects. I have also put those ideas on this page:

I built a  a home-brew 'FT Meter' for the Yaesu FT-857D shown here and a QRP Dummy Load with power measurement and ALC adjustment for QRP operation of the FT-857D shown here.  Previous to those projects I also did a little microphone re-wiring - to be seen here.  I have also made some Baluns and Ununs and while I have not documented the whole projects I have noted down the ideas here. The other thing I have been doing is trying different types of antenna, my Compact Top Band Aerial can be seen here.



Using a Dynamic Microphone with the TS-590s and Microphone Preamplifier ideas:

I would like to be able to use a separate microphone on a boom or gooseneck, so I am bringing together some ideas for a dynamic mic' preamp and separate 'break-out' PTT switch here>

The components required for the small electronic projects were ordered from Bowood Electronics and JAB Electronic Components. ESR supplied a couple of different uni-directional electret microphone elements which are quite difficult to find elsewhere. I just need to find some time to start - sometime after we've moved house! The necessary electrical conduit and aluminium round bar or tubes for the antenna projects will probably be obtained from B&Q.



THE PROJECTS:


EXTENSION SPEAKER With Low Pass Noise Filter


Extension Speaker with Low Pass Noise Filter by M0MTJ
Extension Speaker with Low Pass Noise Filter by MØMTJ  - Read more here >

Here's a nice simple little construction project that will make pleasant use of hour or two and produce a very useful communications speaker. My finished loudspeaker has a pleasant, clear sound and is very efficient, making the most of any transceiver's audio output power. The switchable filter is a nice bonus too.


I have found that most of the small communications extension speakers that I have used have a harsh, resonant and 'tinny' sound that does assist in making speech especially intelligible. Another problem is that many speakers are also quite inefficient - that is to say that they need a good degree of audio power to drive which can mean that the audio amplifier in the transceiver may be run towards its power limitations resulting in undesirable harmonic distortion or even worse, clipping distortion.

To overcome the harsh, tinny audio reproduction requires the use of a larger loudspeaker drive unit. To maximise the available audio output of the transceiver's audio amplifier requires the use of a highly efficient loudspeaker driver unit.

To find out more click here  >
 



FT METER  -  An Analog Meter for Yaesu FT-857D and FT-897D   -   The Homebrew FT-Meter:

FT-Meter - DIY Homebrew project by MØMTJ
FT-Meter - DIY Homebrew project by MØMTJ

Yaesu very thoughtfully added an external meter socket to the FT-857 and FT-897 which is excellent since I like analog S-Meters, so connecting a meter to these radios is child's play. There are no additional circuits required, merely a 100k preset potentiometer and a small microameter. A meter with a sensitivity of 100µA, 500µA or 1mA should be suitable, the final calibration being done with the small internal preset potentiometer, setting the meter for Full Scale Deflection using the calibration setting on the radio.

Parts Required:
Panel Meter with a rating of 100µA, 500µA or 1mA measuring 60mm x 50mm or larger
A case of suitable size to house the chosen panel meter
Small rubber feet for case
Small rubber grommet to feed cable through rear of case
100 k Ohm preset potentiometer
3.5 mm jack plug Right Angled (I show a straight plug in the photographs, but a Right Angled plug is MUCH better!)
A length of thin screened cable - an offcut of RG174 would be fine.



I looked at the Bowood Electronics website and found a very nice little 100µA ammeter measuring about 60mm wide by 50mm high, so I ordered one along with some other components that were in my basket for the QRP power reducer and power measurement project mentioned below.

The construction is very straightforward and should not need much explanation. The physical construction and the method by which the meter is fitted to the case will depend upon what type of meter and case is chosen and will be determined by individual ingenuity.

The electronic construction is very simple indeed comprising a 3.5mm jack plug soldered onto a short length of cable, inner conductor to the tip of the plug and the screen to the ring. The cable is then fed through the rubber grommet that has been fitted into a small hole drilled in the rear of the case.

Internally the screen of the cable is connected to the -ve terminal of the meter.  One of the outer legs of the preset potentiometer is soldered on to the +ve terminal of the meter while the other outer leg of the preset is joined to the centre 'wiper' terminal to which is soldered the inner conductor of the screened cable.

The menus of the FT-857 and FT-897 allow the radio to output indications of Signal Strength; Power; SWR; Modulation; Voltage and Discriminator etc.

Menu 60 -  I have set to 'SIG' to indicate signal strength in receive (RX) mode.

Menu 61 - I have set to 'PWR' to indicate power output in transmit (TX) mode.

The method for calibrating is described below.


FT-Meter circuit diagram drawn by OK2FJ
FT Meter schematic circuit diagram drawn by Frank OK2FJ



FT-Meter - DIY Homebrew project by MØMTJ
(I show a straight 3.5mm jack plug in the photographs, but a Right Angled plug is MUCH better!)

FT-Meter - DIY Homebrew project by MØMTJ
FT-Meter - DIY Homebrew project by MØMTJ
(I show a straight 3.5mm jack plug in the photographs, but a Right Angled plug is MUCH better!)

The physical construction of putting a small meter movement into a case should be very straightforward, but there was the small problem of replacing the 0 - 100µA scale supplied with the standard ammeter with a suitably calibrated and printed scale. Producing a new scale for the meter's dial with a professional appearance was more of a challenge for my graphics / image editing skills!

I searched Google for some helpful images. LDG market two commercially manufactured meters for this job - the FT-Meter and the much larger FTL-Meter; these retail at about £46.00 GBP and £66.00 GBP respectively - my FT-Meter should cost about £10.00, but I digress! The photographs of these products illustrated the layout of the graphics, but nothing that was reproducible for this' home-brew' project.

I was beginning to think that I might have to draw something by hand - then I happened across the website of Frank OK2FJ. Frank has produced an excellent meter scale for his version of the Yaesu FT-Meter. Frank obviously had the same idea as me, to produce a home-brew FT-Meter for a fraction of the cost of a commercial unit, but Frank has greater image editing and graphics skills than mine.

I saved Frank's image file and then made a few of my own simple modifications to the image file using a basic image editing program. The result is shown below and can be downloaded and saved, ready to be re-sized and printed to match the size of the particular meter being used:

S Meter Scale for Yaesu FT-857D and FT-897D - by Mike M0MTJ and Frank OK2FJ
Above: The image graphic for the Yaesu FT-857 and FT-897 meter scale.
Save and print if required.

Printing The Scale: The scale can be printed on paper or thin card and possibly laminated, which is what I did. White paper or card might be the obvious choice, but cream, light green, yellow or light blue card might also make a good background colour.

Measure the horizontal width between the maximum and minimum point on the original (ammeter) scale. (Or with the original scale in the meter calibrate for Full Scale Deflection by entering menu 60 and set it to 'FS'. Then adjust the preset potentiometer so that the needle swings fully to the right and lines up with the maximum point on the scale and measure the distance between the two points.)

Remove the original scale and print out the new scale as a test print and measure the distance between the minimum and maximum points on the new FT Meter scale.

If it's too small, increase the size of the image on the page - using your word processor's functions - and print it again. If it's too big - make it smaller and try again until it's the correct size.
Printing the FT-Meter scale accurately
When printed, the image does need to be scaled very accurately to suit the size of the particular meter movement being used, otherwise the needle will not line up properly with the scale and the indication will be inaccurate. This can be done by trial and error until the correct size is found - a bit of a fiddly and a rather wasteful method. Use a good word processor application such as Microsoft Word or the free Open Office Writer to do this.

Here is an example document file to download and experiment with the size of the final printed image:  FT-Meter.doc


Alternatively a bit of simple math's can be used with an image editing program that allows accurate scaling:

My image editing program allows scaling of the print-out using a sliding scale that shows the total width of the image when it's printed and the dpi (dots per inch) output to the printer. Knowing the total image width isn't especially helpful since what is needed in this case is the dimension that is the distance between the left and right end markers of the S scale - the top curve. My simple image editor does not allow an accurate measurement of a portion of the image, so I did a test print, estimating that the resultant image would need to be 50 mm wide, the output in this case was 920 dpi. I then measured the width of the top curve on the test print, from end marker to end marker - it was 40mm. The scale of the original microammeter is 34mm wide, so the print had to be scaled down in size.

The magnitude of the size reduction can be found by dividing that measurement, 40mm, by the required measurement - in this case 34mm.

40mm  ÷  34mm  =  1.176 (the scaling factor)

The original test print produced an scale that, at 40mm, was too wide. It needed to be 34mm wide. The original image width of the test print was 50mm and therefore this needed to be divided by the scaling factor of 1.176

50mm ÷ 1.176  =  42.5mm

The calculation suggests that 42.5 mm is the width required for the whole image. The image was printed again at that width and the resulting print measured. It was found that the width across the top curve from end marker to end marker was, indeed, the required 34mm.

The other way of doing the scaling is to note the dpi output of the original test print, in this case 920 dpi, and multiply (not divide) that by the scaling factor. The original dpi figure is multiplied, rather than divided, because the dots per inch will increase as the original image size is shrunk. In this case the new, and correctly sized print, is 1082 dpi. Whichever method is used, the second print should produce a scale of the correct size.

Reference: http://www.radio-foto.net/radio/ftmeter2.png This is the original meter scale image that was produced by Frank OK2FJ, I altered this to produce the meter image that is shown above.


Calibration

1/  Enter menu 60 and set it to 'FS'.  Now adjust the preset potentiometer so that the needle swings fully to the right and lines up with the maximum point on the scale - i.e. +60dB on the Signal scale or 15 Volts on the voltage scale.

2/  When the 'FS' has been adjusted accurately, set menu 60 back to 'SIG' and move to step 3.

3/  Enter menu 61. As an initial check set this to VLT.  Exit the menus. Now press the PTT and transmit. The meter should now indicate the voltage - i.e. around 13.2 to 13.8 volts if running from a PSU. Once that is confirmed move to step 4.

4/  Enter menu 61 again and change the value back to SWR, PWR, MOD or ALC (i.e. whatever you want it to indicate when transmitting).

5/  Exit the menus.



For reference the Yaesu manual provides this information about Menus 60 and 61:

MENU MODE No•060 [MTR ARX SEL]
Function: Selects the analog meter display configuration while the transceiver is receiving. Available Values: SIG, CTR, VLT, N/A, FS, OFF. The default is SIG.
SIG: Indicates the incoming signal strength.
CTR: Discriminator center meter.
VLT: Indicates the battery voltage.
N/A: Not available at this time.
FS: Applies a calibration signal (1 mA for full scale) at the METER Jack on the transceiver
bottom, for adjustment of an external meter’s calibration. This lets you adjust
the external potentiometer in your metering system so that the external meter reading
is full scale.
OFF: Disables the meter


MENU MODE No•061 [MTR ATX SEL]
Function: Selects the analog meter display configuration while the transceiver is transmitting. Available Values: PWR, ALC, MOD, SWR, VLT, N/A, OFF. The default is PWR.
PWR: Indicates the relative transmit power.
ALC: Indicates the relative Automatic Level Control voltage.
MOD: Indicates the deviation level.
SWR: Indicates the Standing Wave Ratio (forward:reflected).
VLT: Indicates the battery voltage.
N/A: Not available at this time.
OFF: Disables the meter.


Analog Signal Meter Scale  - S Meter - - by Mike M0MTJ and Frank OK2FJ
Above: The image graphic for a simple analog S Meter scale.
Save and print if required.

Don suggests: You mentioned using card stock for putting a new scale in a meter.  I had very good luck re-labeling a meter by creating an image "photograph size" and then having it printed on photo paper at my local camera shop with my other photos. 73, Don.

John, G0TEV, emailed with a helpful suggestion for those who want to produce a custom made meter scale: Meter Basic is free and will produce a basic linear scale. Meter is a paid for program that will allow  more complex designs such as dB, vu, VSWR and S-meter scales.
Both programs are available here: http://www.tonnesoftware.com/index.html


Felix, EC2ALV, writes: Hi, perhaps this may be of interest to you I use GALVA 1.85 to draw all kinds of scales: variables, pots, meters, etc. for my projects. Just follow the examples and you will learn to use it fast. Kind regards, Felix EC2ALV

Stan, LT4TU, writes: Hello Mike, Please see my FT-meter scale. You can download the original Coreldraw file, designed by me: http://sites.google.com/site/lz4thankyou/projects/ft-meter There is no copyright, I am just happy to share and wanted to let you know.  I made my Ft-Meter in 2006. 73 and GL Stan, LZ4TU (ex LZ2STO).


FT-Meter by Wallace Moodie MM0AMV

Hi Mike, I really like your website, and thought I would just say thank you for all the information contained there. Just built your FT-Meter and chuffed to bits with it......pic attached. Flushed with success I may have a go at your Field Strength Meter next.
Kind regards to both of you. Wallace MM0AMV

FT-Meter by Wallace Moodie MM0AMV
FT-Meter by Wallace Moodie MM0AMV


An update, a few weeks later in December 2013:

Hello Mike, I trust you are well. I know it's sad, but I was laying in bed a few days ago thinking about the FT Meter. Mostly I use my FT897 out in the car working as /P, and I thought it would be handy to be able to keep an eye on the battery charge. I know I can set the original FT Meter to show voltage, but then you lose the signal/power facility. And so Version 2 of your meter was born.

I have also added 12 volt LED lighting for these dark winter days. All the best, Wallace MM0AMV

Version 2 - FT-Meter by Wallace Moodie MM0AMV

Version 2 - FT-Meter by Wallace Moodie MM0AMV

Version 2 - FT-Meter by Wallace Moodie MM0AMV

Version 2 - FT-Meter by Wallace Moodie MM0AMV
Version 2 - Dual FT-Meter by Wallace Moodie MM0AMV
December 2013



FT-Meter by Helmut Rupprechter DJ0FP

Hi Mike, As I  promised here some photos from my “ brand new” FT Meter. I found an 40µA ammeter, the case is made by myself because I could not find the right size. I wanted to make it small as possible so now it is 5x5 cm and 8cm long. It is black!!! Normally I hate black because everthing today is black, black cars and TV`s ,black transceivers and so on. But here it was better because the scale is very small and when the case is black the eyes will focus the white scale.
 
So thanks again for help and have a nice weekend. 73 DJ0FP Helmut Rupprechter.

FT-Meter by Helmut Rupprechter DJ0FP
FT-Meter by Helmut Rupprechter DJ0FP

FT-Meter by Helmut Rupprechter DJ0FP
FT-Meter by Helmut Rupprechter DJ0FP


FT-Meter by Billy McFarland 2MØCSP

FT Meter by Billy McFarland 2MØCSP
FT Meter by Billy McFarland 2MØCSP




Hi Mike,

I came across your website and tried your FT Meter Project.  It works!  I was very happy with it and wanted to share to you what I’ve done. I have incorporated it into my EMACS: Emcomm Modular Ammo Can System. See a photograph of Jesse's FT-Meter here.  Jesse Francis, KJ4KPV.  April 2013


FT Meter by KJ4KPV
More about the Emcomm_Modular_Ammo_Can_System  on this website: http://www.ar15.com
Jesse Francis, KJ4KPV.  April 2013


FT Meter by LU4ADC

Mike, Thanks to the info on your page I was able to build my FT-Meter the way I wanted. I have sent you some pictures. The dial scale is printed on
270gsm paper which worked wonderfully.

Best wishes, LU4ADC

FT-Meter LU4ADC
The large meter that LU4ADC used to construct the FT Meter
 
FT-Meter LU4ADC
The finished FT-Meter by LU4ADC







6 Watt QRP Dummy Load with Power Measurement and ALC Adjustment for QRP Operation:


6 watt QRP Dummy Load with Power Measurement and ALC Adjustment 
6 watt QRP Dummy Load with Power Measurement and ALC Adjustment

Many 100 watt rigs cannot adjust RF power output to a low enough level for QRP operation. What is needed is a circuit to allow control of the ALC circuits to reduce the power of a transceiver for QRP operation with power levels below 5 watts.

Shown below is a very simple circuit for this task - nothing more than a 9 volt battery, a switch, battery connector, 100k resistor and 100k preset potentiometer, a suitable connecting plug, some thin screened cable and a project case. 

When connected to the transceiver it allows a variable negative voltage to be applied to the transmitter's ALC line via the accessory socket. Increasing the applied negative voltage will reduce the transmitter's output power.

ALC adjustment for QRP operation

For QRP contest use the power output will also need to be measured accurately. The second part of this project is to produce a meter that will allow the measurement of voltage from the RF socket to determine an accurate indication of power into a 50Ohm dummy load.

The dummy load shown below uses three 2 watt, 150 ohm resistors wired in parallel to produce the necessary 50 ohm load with a power rating of 6 watts. The resistors can be carbon or metal film, but must not be wire wound due to the undesirable inductive effects that these would cause. For 3 watt operation, the volt meter should read 16.7 volts with a loud whistle into the mic.

QRP Dummy Load with simple power meter


6 watt QRP Dummy Load with Power Measurement and ALC Adjustment

6 watt QRP Dummy Load with Power Measurement and ALC Adjustment

6 watt QRP Dummy Load with Power Measurement and ALC Adjustment

6 watt QRP Dummy Load with Power Measurement and ALC Adjustment
6 watt QRP Dummy Load with Power Measurement and ALC Adjustment


Note from Peter Alice I0YLI in Rome:

Dear Mike,

I am an Italian HAM living in Rome (I0YLI) and my name is Peter, you can have a look at my shack on QRZ.com.  I bought the YAESU FT-897D few months ago and I enjoy it very much. Congrats for your very interesting web-site! Reading along the several articles I found exactly what I need ! Great  - the power reduction by ALC plug of power out-put on FT-897D.

Following given suggestions by your site, I realized the circuit works great in adjusting output power of the FT-897 even at very low level (Noting that the radio must initially be set to minimum power of 5 watts.) regardless modes; FM / AM / SSB  and CW are all OK. (I was using 144MHz & 432MHz).

I noted these important points:
 
1) Input NEGATIVE Voltage at ALC pin MUST-NOT exceed more than -6V ; If a voltage more negative than  -6.1V is be injected to the ALC input, a "suspicious" High-SWR indication will be displayed.
 
2) I realized the "Power Reduction" (made via ALC) start to react at -4V up to -5.5V (Min. Power). Thus the Pot-meter has to scan voltages between -3.9V  to -5.5V . The circuit has been changed: Voltage Regulator = µA-7905 with a Diode in series with its Common pin
    in order to achieve -5.5 V out. On the Ground side of Pot-meter a Resistor of 120K has been added in
    order the knob will cover a total range of about 1.5V (-4V ÷ -5.5V). Such a Pot-meter MUST be "Linear
    Type".
 
3) I tested the circuit at all different RF Power-setting in the User-Menu (5W to 50W) and it works fine.
 
4) Attached are circuit's schematics including component values. I hope these notes will help "experimenters" !
 
After a simulated verification I built the definitive box to give a good appearance (see attached diagram).

Thanks a lot again !

73 de Peter (I0YLI) - Rome.

ALC adjustment by Peter Alice I0YLI
ALC adjustment by Peter Alice I0YLI
ALC adjustment by Peter Alice I0YLI








FIELD STRENGTH METER


It is often said that one of the most useful pieces of test equipment in and around the shack is a Field Strength Meter. A Field Strength Meter can be used to quickly check the presence of RF energy, for example to check that a transmitter is transmitting, for use with antenna experiments such as judging the radiation pattern and efficiency of antenna and for checking RF oscillators etc. It is very useful for making comparative measurements.

To buy a simple ready made FSM would cost around £30.00 and £50.00. Since such a device is simply a form of 'crystal set' without a tuned circuit I set about looking through the junk box to see what electronic components I had that I could use to make a suitable circuit.

This meter will be able to measure field strengths from the 137 kHz up to the the 440 MHz amateur radio bands.

I found a nice aluminium case, a good telescopic aerial, a couple of germanium diodes, a potentiometer, some suitable ceramic capacitors, a nice 250µA signal meter (minus the scale which I had somehow lost) and some other useful bits and bobs. All I needed to assemble a simple yet perfectly effective Field Strength Meter that I am sure is as good as anything that could be purchased ready made - and all made from junk box components!

DIY Field Strength Meter - M0MTJ
Photograph showing the simple construction of the Field Strength Meter



Field Strength Meter schematic
Circuit Diagram of the Field Strength Meter


All the Field Strength Meter has to do is convert the radio frequency signal into a DC current that can drive a meter movement or digital multimeter (DMM). As can be seen from the above circuit diagram the field strength meter bears a great resemblance to a simple crystal set. The differences being that since the field strength meter needs to be sensitive to a wide range of frequencies the tuned circuit (inductor and variable capacitor usually found in a crystal set) is omitted, and rather than headphones or an earphone the output is fed as DC to a signal meter or to a digital multi-meter so that comparative (rather than absolute) measurements can be made.

The telescopic aerial picks up the radio frequency signal and the germanium diode converts the signal to DC. It is important that germanium diodes are used as they exhibit a very small forward bias which is needed to make the meter sufficiently sensitive. |Silicon diodes have a substantially higher forward bias which would substantially reduce the sensitivity, so for this reason it is important to use germanium diodes.

On the same theme it is important to use a sufficiently sensitive meter, so a microammeter will be required. I was lucky to have an old Maplin signal meter with a sensitivity of about 250µA for full scale deflection (FSD) in the junk box, although I would imagine that it would still be worth experimenting with any meter between 50µA to 1000µA.  Alternatively a digital multi meter can be used to measure the output.

The field strength meter that I built has both options selectable with the miniature DPDT switch.  The meter is connected to the digital multimeter with a short fly-lead terminated with a red and black banana plug to identify the positive and negative wires.

The 47K potentiometer allows for the adjustment of the overall sensitivity of the meter.

The advantage of using a DMM is that it has a very high input impedance a therefore will not load the circuit to any great extent, it also enables the meter to be much more sensitive to weaker RF fields if required and also it will be easier to make more precise measurements from the digital readout, particularly small differences.I find that th e DMM is usually set to the 200mV range, or perhaps to 2000mV range if the RF field is especially strong.

The value of the various components is not particularly critical, but as mentioned, the diodes must be germanium rather than silicon and any diodes such as OA90,OA91, OA80, OA81, OA47 could be used.

Field Strength Meter Parts List:

2 off OA91 or any similar Germanium Diodes

1 off 470 pF ceramic capacitor (code 471)

1 off 0.01 µF ceramic capacitor  (code 103)

1 off 0.047 µF ceramic capacior  (code 473)

1 off 47 K Ohm linear track potentiometer

1 off 250 µA signal Meter

1 off Telecopic Aerial about 20 inches long

1 off Red Banana Plug

1 off Black Banana Plug

Small Aluminium or Plastic Case

2 off Rubber Grommets

Hook Up Wire
DIY Field Strength Meter - M0MTJ
Photograph of completed Field Strength Meter

Hello Mike, I've just finished your Field Strength Meter and it works great. Your website is a gold mine of information, and once again thanks you for all your work. I have attached a photograph of the finished item. I decided to go with terminals for the DMM rather than the flying leads. Kind regards, Wallace. MM0AMV

Field Strength Meter by Wallace - MM0AMV
Field Strength Meter by Wallace - MM0AMV




DYNAMIC MICROPHONE FOR THE KENWOOD TS-590s - or indeed many other rigs

The February 2012 edition of Practical Wireless magazine included a competition to win a Heil HM-12 Genesis microphone, a new model from Heil, and adapter cable. I wasn't happy with the hand microphone supplied with the Kenwood TS-590s, so naturally I entered to competition hoping to win a prize worth over £100.00! - I didn't win however.
Heil HM-12 Genesis - dynamic microphone
While the audio quality of the Kenwood microphone is excellent, I find that the microphone casing is very 'creaky' in operation and unless one holds it very gently, it produces a lot of nasty, undesirable creaky noises on air. I tried tightening the case and also placing sponge and other soft materials inside the case, but to no avail - it still creaks.

However it also made me think that, tucked away somewhere in my boxes of "junk", I had a dynamic microphone with cable, mic clip and a goose neck. After searching the shed I found the Radio Shack / Tandy Optimus 33-7058 unidirectional dynamic microphone and its accessories. I believe that the microphone was originally listed at about £30.00 or £40.00 but I purchased it for £10.00 in a sale. 

Noise Reduction: 
The bonus of using a Uni-Directional microphone mounted on a boom, stand, or goose-neck is that it will be isolated from noises caused my movement of hand and fingers and, being directional, will help reduce sounds from the rear, such as the whirring fans in radios, power supplies and computers.

To use it I needed to make up a cable to connect between the microphone and transceiver and also provide a break out cable for a separate PTT switch - either a hand switch or a foot switch.

A Heil cable would cost about £37.00, the Heil hand switch £39.00 and a Heil FS2 or FS3 footswitch also about £30.00. The Heil HM-12 microphone itself costing £70.00 with an HB-1 'anglepoise' desk mounted boom costing about £69.00 a complete mic system would cost around £216.00. With the things that I already had I thought that could put a separate microphone system together for under £20.00.



Making A Microphone Adapter Cable: 
For microphone pin outs see this page: http://homepage.ntlworld.com/rg4wpw/date.html

I had some suitable cables that could make a new microphone lead and the PTT lead, but if the cable had to be bought new it would probably have cost no more than £5.00. I had to buy an 8 pin mic plug (8 pin in-line socket) for £2.00 and a 6.3mm inline socket for £1.60 but I had a couple of 6.3mm jack plug for the hand switch, but that would cost about £1.60 if bought new. I also found something that could be used as a hand PTT switch in the junk box.....

I retreived a 'panic button' from a bin that had been discarded from a PMR radio installation and saved it for some future use. I thought it could be used as a hand held PTT switch as it had a 'momentary' switching action required for push to talk applications and cost was zero. I had nothing for a foot switch, but I found a nice one of metal construction made by the Eagle brand for use with musical instruments such as keyboards. That cost only £7.00, so with having many components in the 'junk box' the total expenditure was around £11.00.

Momentary Action switch:It's important that any switch considered for the PTT function has a momentary action - push for ON and release for OFF i.e. it is non latching and the contacts only connect and complete the circuit when pressed, disconnecting again when the button is released. Some foot switches are latching (which will not be suitable) and others may have the useful option to be wired for either push for on and release for off, OR push for off and release for on.

Preparing the parts for the homebrew microphone adapter cable
Preparing some of the parts for the homebrew microphone adapter cable
In-line XLR Socket (Plugged into microphone); 6.3mm in-line Socket for PTT switch;
6.3mm mono jack plug for PTT switch, 8 Pin in-line socket (plug) to connect to the radio; Shielded microphone cable.


PARTS REQUIRED:  (Approximate new prices 2012 - you may well find some of these items much cheaper)

2 or 3 metres of shielded microphone cable - 2 core for standard mic's or 4 core for Heil mic's with PTT switch.  £5.00
2 metres of 2 core, or shielded single core cable for the break out PTT switch.    £2.00
8 pin in-line socket ("microphone plug") for transceiver (or whatever connector is required for the particular rig check here: rg4wpw/date.html). £2.00
In-line, female, XLR socket to connect to microphone. 3 pin for many mic's or 4 pin for some Heil mic's. (Check heilsound.com). £2.00
6.3 mm (1/4") in-line jack socket to terminate the break out PTT cable.  £1.60
6.3 mm (1/4") jack plug to fit to the PTT switch.   £1.50
Momentary push-to-make switch or button for the hand held PTT switch. £2.00
Small plastic case to house the hand held PTT switch.  £2.00
Eagle G028B Foot Switch or one of many similar available.  £7.00
Goose-neck with base  £11.00 to £14.00   -   or Articulating Boom. £30.00 to £50.00
Dynamic Uni-Directional Vocal Microphone (Good quality e.g. AKG; Audio Technica; Beyerdynamic; Behringer; Heil;
                                                                                                                                                           Sennheiser or Shure) from about £25.00 to £70.00

TOTAL WITHOUT MICROPHONE £36.00 to £76.00  (approximate)
TOTAL WITH  A MICROPHONE £61.00 to £107.00   (approximate)  i.e. at the very worst, still half the price of a full Heil kit.


Radio Shack / Tandy Optimus 33-7058 unidirectional dynamic microphone - Microphone and homebrew microphone adapter cable
Microphone and the completed home-brew microphone adapter cable project with the
finished hand PTT switch below.


Foot Switch - Eagle Ref number G028B
Above: Eagle G028B Foot-switch. A foot switch made by the Eagle brand that I bought for the bargain price of £7.00. Reference number G028B.  It's intended for use with musical instruments, such as keyboards, but it works well as a PTT foot switch and is of metal construction and has the required momentary action.

A search of the internet retail sites should reveal a multitude of similar momentary, push to make, foot switches.
Hand Switch
Above: A panic button discarded from a PMR radio installation that I 'picked up' from the bin and saved for some future use. Now it is adapted as a hand held PTT switch by adding a jack plug!


Kenwood TS-590s Microphone Socket
Above: Kenwood TS-590s Microphone Socket

Link: For microphone pin outs see this page: http://homepage.ntlworld.com/rg4wpw/date.html



Diagrams for Microphone XLR Sockets

The 'plugs' that connect into the bottom of a microphone are actually in-line XLR sockets (famale), the 'socket' at the bottom of the microphone is actually the plug (male) part of the XLR system. Wiring for this and similar applications:

Pin 1 of the radio's 8 Pin microphone socket is connected to Pin 2 of the microphone's XLR connector  (MIC +ve)
Pin 7 of the radio's 8 Pin microphone socket is connected to Pin 3 and 1 of the microphone's XLR connector (MIC -ve and SHIELD)

Pin 2 of the radio's 8 Pin microphone socket is connected to the separate PTT breakout cable and 6.3mm In Line Jack Socket centre pin
Pin 8 of the radio's 8 Pin microphone socket is connected to the separate PTT breakout cable and 6.3mm In Line Jack Socket body (SHIELD)

Diagrams as viewed from the front of the in-line female XLR socket  ("Mic Plug"):

3 Pin XLR
Used on many microphones including
the Optimus 33-7058 which has
an unbalanced output.

Unbalanced Output:
PIN 1    SHIELD.
PIN 2    +ve MIC.
PIN 3    -ve MIC connected to pin 1


*For microphones with a Balanced Output:
PIN 1    SHIELD.
PIN 2    +ve  MIC OUTPUT
PIN 3    -ve  MIC GROUND
4 Pin XLR
As used on the Heil HM-12 Microphone
http://www.heilsound.com/amateur
 
PIN 1    GROUND/SHIELD.
PIN 2    MIC.
PIN 3/4  PTT.
XLR Connector - 3 Pin

*Microphones with a Balanced Output: Professional quality microphones, such as the Shure models mentioned on this page, have a Balanced Output where Pin 1 is Shield; PIN 2 is +ve Mic Output and PIN 3 is -ve Mic Output.  However if an unbalanced connection is required it should be possible to simply connect Pin 3 to Pin 1 inside the inline XLR socket that plugs into the base of the microphone to create an unbalanced connecting cable. Ideally the balanced cable would be preserved and suitably configured, i.e. balanced, microphone amplifier circuit or an audio transformer used at the rig end. Balanced mic cables reduce noise hum and RF pick up.


Microphone Specifications  -  comparison between the Optimus 33-7058 and Heil HM-12

Optimus 33-7058 Microphone Frequency Response Curve & Polar Diagram
Optimus 33-7058 Microphone Polar Diagram &
Frequency Response Graph

Optimus 33-7058 Microphone Specifications:
Type ..................................................................  Dynamic      (Balanced output via XLR connector)
Directvity ..........................................................  Unidirectional
Impedance ........................................................  500 Ohms +/-30% (at 1,000 Hz)
Sensitivity (at 1 kHz) .......................................   -75 dB  +/-3 dB (0 dB = 1V/microbar)   i.e -55db re 1V/Pa  or  1.78  mV/Pa
Frequency Response .........................................  60 - 15,000 Hz
Cable Dimensions (Length x Diameter) ..............   5 meters x 5.5 mm
Microphone Dimensions (Length x Diameter) ..... 161.5 x 51 mm
Plug ........ .. ................ . ..................................... 6.35 mm (1/4 inch) Jack Plug
Included Accessory ............................................. Microphone Stand Adapter & Zippered Carrying Bag
5 Meter Microphone Cable with XLR Connector and 6.35 mm Phono Plug  (cable supplied with unbalanced configuration)
Weight . ............................................................... 198 g (Excluding Cable)

The output will not be enough for many Icom rigs, particularly older ones that have insufficient microphone pre-amplification. In this case an electret microphone with around a -42 to -45dB sensitivity (7.0 to 5.6mV/Pa/1kHz) may be more suitable, or an add-on home-brew pre-amplifier could be constructed - perhaps like this >

Heil HM-12 Microphone Specifications:
Type ..................................................................  Dynamic, moving coil, copper wound, mylar with internal shock mount
Directvity ..........................................................  Cardioid - exhibiting nearly –35 dB of rear rejection
Impedance ........................................................  1000 ohm
Sensitivity ................ ........................................  -55 dB       (no reference specified by Heil but presumably dB re 1 V/Pa )
Frequency Response .........................................  80 Hz - 14 kHz @ -55 dB  +4 dB peak centered at 2 kHz
Connection.........................................................  4 pin XLR
Included Accessory ............................................. Microphone Stand Adapter
Weight . .............................................................. 250 grams (8.8 oz) (Excluding Cable)
Cable required...................................................... HEIL CC-1 Connecting Cables. (cable with unbalanced configuration)
‘Soft touch’ PTT switch is wired to pins 3 and 4 for transmitter control with the microphone signal fed to pins 1 and 2 of the 4 pin XLR.


Link: Microphone Sensitivity Calculations: http://www.sengpielaudio.com/calculator-transferfactor.htm



AUDIO TAILORING   -  Filtering  /  Carrier Point  /  DSP:

Microphones of this type are very good for sound recording and hi-fi applications as they have a good wide frequency response of 60 Hz to 15,000 Hz. However as with all cardioid / unidirectional microphones, this mic' exhibits the "proximity effect" which can make the low frequency bass response rather too full for efficient communications audio.

For best intelligibility good communications audio should have a range of around 400 Hz to 2600 Hz - this is particularly important for spectrum efficiency so as not to hog a wide bandwidth and cause unnecessary QRM to other users desperately trying to find a bit of clear space on the bands!

Proximity Effect graph - Shure Micophone
http://www.shure.co.uk
Above: A graphic representation of the 'Proximity Effect' - an effect of directional microphones whereby the
bass output rises as the distance to
the microphone decreases. Different makes and models of microphone
will vary significantly. Some models are designed to minimise the proximity effect to some extent, e.g. the Shure SM-48.

Large amounts of bass output are undesirable for clear, intelligible, communications speech.


Spectrum and Power Efficiency: For spectrum efficiency and best use of transmitter power - not to mention good manners and simple consideration to other users - for SSB transmitters to be ITU compliant the audio bandwidth should be no wider than 300 Hz to 2700 Hz. After all SSB communications do not need to be "Hi Fi" - just clear and spectrum efficient - I don't need to be WABC! A wide transmission can cause great annoyance to adjacent channel operators who are trying to find a little bit of clear space, only to be splattered!


Narrow Filter: Appropriate audio bandwidth may be achieved by the use of a narrow filter within the radio, either a mechanical or DSP IF filter.


Carrier Point:  In the Icom IC-706, for example, by using Menu Q4 the bass response can be rolled off by setting the Carrier Point to Carrier Point +100. Adjusting the Carrier Point for TX is equivalent to I.F. Shift in RX. (The Icom IC706 and other older Icom rigs, has comparatively low microphone gain and will need a microphone pre-amplifier if using most standard dynamic microphones. Dynamic mic's have lower electrical output than the electret microphones for which the radio is designed.)


DSP:  TS-590s: With the Kenwood TS-590s I found that, as a minimum, it was necessary to set DSP TX filter for SSB/AM low cut to 400 Hz [Menu 25], leaving the DSP TX filter for SSB/AM high cut at the default 2,700 Hz [Menu 26]. Matters could be further improved by use of the DSP audio equalizer:

Whereas I found the DSP TX equalizer [Menu 30] was best set to C (Conventional) or HB2 (High Boost 2) best with the supplied Kenwood hand microphone, I found that the HB1 (High Boost 1) setting was better with the Optimus dynamic microphone. HB1 reduces the low frequency response slightly more than HB2. The best results were obtained by using Kenwood's ARCP-590 computer software to custom tailor the U (User) setting with a little more high boost and a little more low cut than with the HB1 setting using the on screen graphic equalizer.


Mic Gain and Processor: Initial starting points with Optimus dynamic mic were:   Mic Gain 50 - 60   |   Proc In 40 - 50   |   Proc Out 50 - 60



Designing and constructing some input filtering:

For radios without adjustable filtering or comprehensive DSP control a simple high pass filter using a capacitor an resistor arrangement similar to that shown below might usefully reduce low, bass, response and not only make the audio clearer but also reduce bandwidth and unnecessary splatter affecting other users on a crowded band. Use the formula fc = 1/(2πRC) to find the -3dB cut off frequency.
Where R is resistance in Ohms and C is Capacitance in Farads  (note 1µF = 0.000001F)


Note: For proper loading of a typical dynamic microphone with an impedance up to 600 Ohms, a microphone preamp for should ideally have an input impedance of between 1200 Ohms and 3000 Ohms. Read much more detail on this important subject on this external link.


Some examples:

In the example below if the resistor was 1.2k Ohms and the capacitor was 0.47µF the cut off frequency (fc) would be 282 Hertz. If the capacitor was 0.22µF then the cut off frequency would be 603 Hertz. (Incidentally these are the values used in the Kenwood MC-90 desk microphone). If the capacitor was 0.33µF then the cut off frequency would be 402 Hertz.

Using a 12k Ohm resistor the capacitor value would be 0.047µF (47nF) to provide a cut off frequency of 282 Hertz, a capacitor value of 0.033µF (33nF) would provide an cut off frequency of 402 Hertz or a capacitor value of 0.022µF (22nF) for a cut off frequency of 603 Hz.

Using a 2.2 k resistor may possibly be more appropriate, so here are some recalculations that include some capacitor values that are achieved by using capacitors connected in parallel. e.g: 2.2k Ohm + 220nF + 22nF = fc 299 Hertz   or   2.2k Ohm + 100nF + 47nF =  fc 492 Hertz. This is done because using standard value capacitors would produce some inappropriate & widely spaced cut-off frequencies.




Rod Elliott - Elliott Sound Productions: 1st Order Filter arrangement for non inverting op-amp (by Rod Elliott - ESP Sound Products)
Filtering with a non-inverting operational amplifier arrangement  -  fc = 1/(2πRC)
First Order High Pass Filter
  ESP Elliott Sound Products




M0MTJ - Parts for a homebrew (DIY) hand PTT Switch
Another idea for a homebrew (DIY) PTT hand switch and the parts required  -  M0MTJ

Momentary Contact Button for PTT switching;  A length of shielded cable;  A 6.3mm jack plug;  A small plastic enclosure.
Cost? £5.00 to £7.00 ?


Gooseneck microphone support

Above: Various length Goosneck microphone supports generally available in 6 inch (155mm), 13 inch (330mm) and 19 inch (480mm) lengths which could also be joined together to form a longer length. Requires fixing base and microphone holder.
 http://www.promusicaustralia.com
http://www.maplin.co.uk

Right: A typical articulating 'anglepoise' microphone boom. This is the MS01 broadcast type microphone stand sold by Woodbrass.com at a cost of around £28.00 plus carriage.

Other similar booms are available from around £50.00 and upwards. The Heil HB-1 is available for around £70.00.

http://www.heilsound.com/amateur/

http://www.woodbrass.com
MS01 BROADCAST TYPE MICROPHONE STAND


Link: Microphone Sensitivity Calculations: http://www.sengpielaudio.com/calculator-transferfactor.htm





MORE ABOUT MICROPHONES


Shure SM48 dynamic cardioid microphone
Is there one of these lurking in a cupboard somewhere? A typical dynamic microphone - Shure model SM48 -  http://www.shure.co.uk
Unlike the Optimus 33-7058 the Shure microphone has higher output which could be useful, see spec's  below:


Transducer Type: ......................Dynamic
Polar Pattern: ...........................Cardioid
Sensitivity (1 kHz):................. -57.5 dBV/Pa / 1.33 mV/Pa
Frequency Response:............... 55 Hz - 14 kHz
Tailored for vocals, with brightened mid-range and bass rolloff to control proximity effect.
Shock-mounted cartridge for exceptional ruggedness and reduced handling noise. Built-in "pop" filter that reduces explosive breath sounds and wind noise.
Weight:.................................... 370 g
Shure SM48 frequency response graph
SM48 Frequency Response graph
Transducer Type:...................... Dynamic
Polar Pattern:........................... Cardioid
Sensitivity (1 kHz):.................. -56 dBV/Pa / 1.6 mV/Pa
Frequency Response:............... 70 Hz - 15 kHz
Tailored frequency response is smooth and extended. Tuned specifically for vocal applications. Dynamic cartridge has a simple, rugged coil. Cartridge includes a neodymium magnet for high output level. Durable metal construction. Steel mesh ball grille with integral "pop" filter reduces explosive breath sounds and wind noise.
Weight:..................................... 324 g
Shure PG48 frequency response graph
PG48 Frequency Response graph

Shure also produce the famous SM58 vocal microphone which has a flatter wider frequency response than the SM48 & PG48 which, perhaps, may be a disadvantage for amateur radio use; the mid-range lift and more rolled off bass response of the SM48 and PG48 might be more desirable for clearer speech. Having said that, the SM58 minimizes proximity effect which could be useful. http://www.shure.co.uk


Beyerdynamic TG V35d s    Specifications
Transducer type . . . . . . . . . . . . . . . . Dynamic
Operating principle. . . . . . . . . . . . . . Pressure gradient
Polar pattern . . . . . . . . . . . . . . . . . . Supercardioid
Frequency response:
Close miking . . . . . . . . . . . . . . . . . . 30 - 18,000 Hz
Distant miking (measured at 1 m) . . . 55 - 18,000 Hz
Rear attenuation at 1 kHz. . . . . . . . . > 20 dB at 140°
Open circuit voltage at 1 kHz . . . . . . 2.5 mV/Pa = -52 dBV
Nominal impedance . . . . . . . . . . . . . 600 Ω
Load impedance. . . . . . . . . . . . . . . . 2 kΩ
Connection . . . . . . . . . . . . . . . . . . . 3-pin XLR male
Dimensions . . . . . . . . . . . . . . . . . . . Length: 186 mm
Shaft diameter: 24/38 mm :   Head diameter: 50 mm
Weight without cable. . . . . . . . . . . . 305 g

Beyerdynamic TG V35d s microphone frequency response

Beyerdynamic TG V35d s microphone
Beyerdynamic TG V35d s


Other suitable very high quality microphones may include the Beyerdynamic TG V35ds  or TG V50d and AKG Perception Live P3 or P5 or D5 - The AKG D5 is a microphone that is said to challenge the Shure SM58 as a high quality vocal mic. The Thomann t.bone MB 95 is a budget high output microphone with very crisp clear reproduction that should produce very clear speech, it is also a bargain price of around £20.00 in 2012 www.thomann.de.


Link: Microphone Sensitivity Calculations: http://www.sengpielaudio.com/calculator-transferfactor.htm



Microphones with a Balanced Output: Professional quality microphones, such as the Shure models mentioned on this page, have a Balanced Output where Pin 1 is Shield; PIN 2 is +ve Mic Output and PIN 3 is -ve Mic Output.  However if an unbalanced connection is required it should be possible to simply connect Pin 3 to Pin 1 inside the inline XLR socket that plugs into the base of the microphone to create an unbalanced connecting cable. Ideally the balanced cable would be preserved and suitably configured, i.e. balanced, microphone amplifier circuit or an audio transformer used at the rig end. Balanced mic cables reduce noise hum and RF pick up.
See balanced microphone preamplifiers here  and  also here.




Dynamic Microphones designed specifically for amateur radio use:

Heil HM-12 Genesis microphone  The Heil HM-12 Genesis dynamic microphone I am told, uses Heil's new HC-6 dynamic element and therefore has a higher output than some typical dynamic mic's. The frequency response is 80 Hz to 14 kHz together with the hallmark Heil +4dB lift at 2kHz to enhance the clarity of the audio and unlike a standard dynamic hand microphone, the HM-12 also has a built in PTT switch.

Too Expensive? - The HM-12 might seem rather expensive at £70.00 when you consider that a microphone such as the t.bone MB 95, which as very crisp clear vocal audio, can be bought for £20.00 from www.thomann.de , even a high quality vocal microphone such as Beyerdynamic TGV 35d s can be bought for about £45.00 from many authorized dealers such as www.soundexposure.com


Heil HC-6 & the new Gold Elite microphone  -  Heil Press Release for the HC-6 dynamic element: "
Heil Sound Introduces New HC-6 Dynamic Microphone Element: Official Introduction at the Dayton Hamvention May 14, 2010. Heil Sound revolutionized amateur radio audio with their tailored response HC Series elements in 1982, which allowed the non-DSP transmitters of that era to produce different transmit responses by selecting the right microphone element.

Fast-forward 30 years. Bob Heil has designed the new Heil HC-6 that, by adjusting the DSP EQ of the modern transceivers, will produce Beautiful, full range broadcast audio as well as narrow response contest/DX audio of the Heil HC-4 all from this one specially designed dynamic microphone element. The many 'voices' of the HC-6 are truly amazing. Using a .82 inch diameter Mylar diaphragm, the - 3dB points of the wide frequency range is set at 100Hz and 12.5 kHz. With sensitivity of - 57dB at 600 Ohms nominal output impedance centered at 1 kHz. The HC -6 Audio response can be equalized to match just about any requirements."

The HC-6 element is used in the Gold Elite microphone "
The new Gold Elite microphone is designed and crafted specifically for amateur radio communications. It contains two distinctly different high performance dynamic elements that are available at the flip of a switch to meet the different types of communications. The WIDE position has the HEIL Elite full range element producing smooth articulate 60Hz – 16 kHz audio with the traditional Heil +4 dB peak centered at 2 kHz. This gives the new Gold Elite excellent voice articulation". "The NARROW position features the new HC-5.1 dynamic element. In 1982, Heil Sound revolutionized amateur radio audio with their tailored response HC-4 and HC-5 elements for radios that had NO tone adjustments". "The HC-6 is designed to respond to those older rigs as well as today’s transceivers with on-board DSP EQ. The HC-6 produces full range broadcast audio as well as the tailored DX/Contest audio by simply adjusting your DSP EQ". http://www.heilsound.com/amateur
Spec's
HC-6 wide.............................: 60 Hz - 16 kHz @ -55 dB at 600 Ohms
HC-6 wide  -6dB points.....: 100Hz - 12.5 kHz @ - 57dB at 600 Ohms
HC-5.1 narrow..................... 200 Hz - 8 kHz @-58 dB  at 1000 Ohms

Heil HC-6 Frequency Response Graph
Heil HC-6 Frequency Response Graph

Heil HC-4 Narrow, HC-5 and GM Wide Comparison
Heil HC-4 Narrow, HC-5 and GM Wide (not Gold Elite) Comparison  Frequency Response Graph


Heil HC6 Comparison frequency response graph
Above graph from VK1OD - http://vk1od.net
Other graphs and information from Heil Sound   -  http://www.heilsound.com/amateur   






MICROPHONE PRE-AMPLIFIER IDEAS

Is there a hand held dynamic 'stick' microphone lurking in a drawer or cupboard somewhere?

Rather than always using a hand held microphone I have experimented with a different microphone that can be suspended from a boom or goose-neck. I have a good quality Optimus dynamic microphone that I have found works well the the Kenwood TS-590s - see above.

However the Icom IC-706MK2G is not best suited to dynamic microphones due to their low output and the 706, like many Icom radios, not having sufficient microphone amplifier gain. One route to take would be to use an electret condenser microphone or microphone element which have higher output than many dynamic microphones. I also have a couple of different unidirectional electret condenser elements to experiment with.

To use a typical low impedance, lower output dynamic microphone would require some additional amplification with the Icom and would likely also require some additional filtering to roll off undesirable bass response that would make the transmitted audio less intelligible at RX. I therefore had a look at what might be required to build a simple external microphone preamplifier to compensate.

Building an external amplifier would also allow experiments with some simple audio filtering, particularly concentrating on a low pass filter to roll off audio frequencies below a certain point, say below 300 Hz or below 400 hertz, for example.




Basic Microphone preamplifier using simple inverting op-amp arrangement  -  Needs Development Work! :
Microphone op-amp
  Typical Inverting Operational Amplifier configuration

[ Read about experiments with a microphone preamplifier circuit HERE > > ]






ICOM HM-103 MICROPHONE MODIFICATION for the IC-706mk2g

When I first got my Icom IC-706mk2g I had several reports of quiet audio that could not be fully corrected by using mic gain or compressor controls. It was suggested by a couple of fellow radio amateurs that I modify the HM-103 microphone that is supplied with the IC-706 radio. The modification was done in this way:

The microphone casing is opened by removing the three screws on the rear panel. It is very important to hold the PTT switch in place while doing this otherwise it will come adrift and the spring could fly out and be lost!

Next remove the three screws that hold the circular metal plate in place. Then remove the two very tiny screws that hold the small PCB in place. Behind this PCB is located the electret microphone element. Remove the electret element and also the rubber gasket.

After discarding the rubber gasket the microphone could be fully reassembled and tested for audio improvements - it should be noticeably better, but if it's still not satisfactory the modification could be taken one stage further:

Remove the circular metal plate and electret capsule again. Then, using a sharp modelling knife or scalpel, scrape away some of the plastic from the molding that holds the electret capsule in place to enlarge the aperture between the capsule and the larger circular area under the metal plate - where the sound enters from the exterior of the microphone's casing - as shown in the photograph below. This should allow more volume to reach the electret capsule and provide greater drive and punch to the rig.

I have had no complaints about low audio since doing these modifications.

Icom HM-103 Microphone modification for IC-706mk2g
Icom HM-103 Microphone modification for IC-706mk2g by M0MTJ

Icom HM-103 Microphone modification for IC-706mk2g
Icom HM-103 Microphone modification for IC-706mk2g by M0MTJ









WIRING A CABLE FOR A DIFFERENT MICROPHONE


I decided to use my existing Leson (Altai) TW-232 Desk Microphone as an alternative to the Icom HM-103 hand mic that is supplied with the Icom IC-706MK2G transceiver.

The TW-232 desk mic is fitted with a standard type 6 pin mic plug wired for my Midland 48 Excel CB radio. The Icom 706 has a completely different RJ45 type mic socket. I needed to make a 'cross-over cable' to fit between the mic plug on the TW-232 and the Icom 706 transceiver.

Looking at the circuit diagram for the Icom IC706, the basic wiring only needs four wires: PTT (Push To Talk transmit switch), PTT Ground, Microphone Audio and Microphone Audio Ground.

This is slightly different to CB wiring which does not have separate grounds for PTT and Mic, inside the plug on the TW-232 microphone these two ground wires were connected together. I therefore I separated the MIC Ground and PTT Ground within that plug.

This would require two Cross-over cables; one for the CB that re-combined the two grounds together to match the wiring scheme required for CB and the second cross-over cable for the connection to the IC706Mk2G.


Here is the wiring scheme for the TW-232 mic and the Icom transceiver:

The Leson (Altai) TW-232 desk microphone wiring is as follows:

White = 
PTT
Black = PTT / Receive Ground
Blue   = Receive
Red   =  Mic audio
Shield = Shield (mic audio shield)



Icom IC706Mk2G microphone plug wiring for RJ45 plug:

1 =  +8 volts d.c.   *** Do not connect & be careful NOT to short out otherwise the radio will be damaged ***
2 =  Frequency up/down buttons
3 =  Audio output
4 =  PTT      >>>>>>>>>>>>>>>>>>>>
Connects to the White wire of the TW-232 Mic
5 =  GND - Microphone Ground >>>>>> Connects to the Shield wire of the TW-232 Mic
6 =  Microphone audio input   >>>>>>>> Connects to the Red wire of the TW-232 Mic
7 =  GND - PTT Ground     >>>>>>>>>> Connects to the Black wire of the TW-232 Mic
8 =  Squelch control



Leson / Altai TW-232 wiring diagram

Above:  Leson / Altai TW-232 wiring diagram
*Important: Please check that the colour coding of the wiring of your TW-232 microphone
is the same as that shown above - if not note the differences and proceed accordingly



Wiring diagram for Icom HM-103 microphone
Wiring diagram for Icom HM-103 microphone
shows the microphone socket as seen from the front of the radio
  (Icom Corporation)


Icom IC-7000   The wiring for the IC-7000 would be similar for the TW-232 microphone (see TW-232 diagram above)

1 =  +8 volts d.c.   *** Do not connect & be careful NOT to short out otherwise the radio will be damaged ***
2 =  Frequency up/down buttons
3 =  HM-151 connection
4 =  PTT      >>>>>>>>>>>>>>>>>>>> Connects to the White wire of the TW-232 Mic
5 =  GND - Microphone Ground >>>>>> Connects to the Shield wire of the TW-232 Mic
6 =  Microphone audio input   >>>>>>>> Connects to the Red wire of the TW-232 Mic
7 =  GND - PTT Ground     >>>>>>>>>> Connects to the Black wire of the TW-232 Mic
8 =  Squelch control  (HM-103) or Data in (HM-151)

Icom IC-7000 microphone wiring for HM-103 and HM-151
Above - Microphone wiring for HM-103 and HM-151
pertaining to the Icom IC-7000 transceiver
  (Icom Corporation)



The Up / Down frequency buttons are not wired in my cross-over cable, but could be used if required if additional switches were fitted into the desk mic.  The basic wiring only requires four wires to pins 4,5,6 & 7 in the RJ45 plug - as seen below:

The RJ45 plug fitted to a short piece of mic cable
The RJ45 plug fitted to a short piece of mic cable

Fitting the RJ45 plug to the mic cable
Fitting the RJ45 plug to the mic cable

Fitting the mic socket on the other end of the cable
Fitting the mic socket on the other end of the cable

The completed cross-over cable
The completed cross-over cable


Thanks to Alex and Dave at the Charlie Delta ARC for the necessary plugs that enabled me to make this cross-over lead. Cheers guys!!






MORSE CODE PRACTICE OSCILLATOR


Morse code practice oscillator project
Internal view showing PCB and other components

Morse code practice oscillator project
               The completed CW Practice Oscillator with Morse Key

Morse Code practice oscillator using 4047B CMOS integrated circuit
Morse Code practice oscillator using 4047B CMOS integrated circuit

Parts Required:
4047B CMOS Integrated Circuit
BFY51 Transistor
1M Ohm Preset Potentiometer - skeletal or enclosed, horizontal or vertical depending on physical layout
22k Ohm linear Standard Potentiometer
Small Knob for 22k potentiometer
100k Ohm carbon or metal film resistor, 0.25 or 0.6 watt
150 Ohm carbon or metal film resistor, 0.25 or 0.6 watt
1nF ceramic or monolithic ceramic capacitor
6.3 mm (1/4 inch) Jack Socket for connecting morse key
15 Ohm miniature loudspeaker
PP3 9 volt battery
PP3 battery clip
Vero Board
Project Case
Kit Available Here






SHORT LOADED TOP BAND ANTENNA  
FOR 160 Metres / 1.810 to 2.0 MHz

My experimental project during 2009 was trying to accommodate a small top band antenna in the restricted space at my QTH.

A full size aerial for Top Band is going to be far too big for most back gardens, but the basic requirement really is to get as much aerial wire in the air as possible - the longer the better - and then load the antenna to bring it to resonance on the band. I used a small inductor wound on a 50mm diameter plastic tube. A top band aerial like this also needs the very best earth possible - i.e. as many ground wires as can be accommodated.

I gradually refined my ideas and have now put the results on the antennas page
here

Top Band Inverted L Aerial - shortened for small gardens - by M0MTJ
Shortened Loaded Top Band Antenna For Small Gardens

Read More On The Antennas Page Here >









BALUN and UNUN CONSTRUCTION


I needed a 4:1 Balun for my Delta Loop antenna, so I built one inside a 100mm x 100mm  IP54 weatherproof box. It is wound on a T200-2 toroid core using 1.2mm diameter / 18 s.w.g. enamelled copped wire and so should handle about 400 watts:

4:1 Balun by M0MTJ
The Feed Point of the Delta Loop Antenna is fed via this 'home brew' 4:1 balun by M0MTJ


Previously I had constructed a smaller 4:1 balun in a non weatherproof enclosure. This is wound on a T157-2 toroid core which should handle about 200 watts.

4:1 Balun by M0MTJ
Simple 4:1 Balun by M0MTJ

* * *

A Small Combined Balun / Unun for Portable Use:

Small compact antenna tuning units such as the LDG Z11 Pro or MFJ 945E, for example, do not have a built in 4:1 balun so, depending on the type of aerial being used a balun (or unun) may well be needed and so should be added to the equipment list.

A resonant dipole or doublet fed with twin lead for lightness will need a 4:1 balun at the ATU. Alternatively a simple vertical (random length) wire up the 7 metre tall fishing pole with a counterpoise run along the ground could be used. Such an aerial would use an Unun as a more appropriate matching device.

To save having to carry both a 4:1 balun and a 4:1 unun, I decided to make a combined Balun / UnUn unit housed in a small plastics case. Since an Unun is merely a balun with the PL259 socket wired in reverse (see diagrams below) it seemed logical to make an impedance transformer with two SO239 sockets; one wired as a Balun for doublet antennas and the other wired as an UnUn configuration for unbalanced antenna wires.

As a quick test I fixed a 7.2 metre length of wire to my fishing pole, supported vertically, and ran out a similar length of counterpoise wire. Connected to the Baln/Unun unit with the coaxial feeder connected to the UnUn socket, I could obtain an easy match using my MFJ-945E on 40m; 17m; 15m; 12m and 10 metres. Surprisingly 20 metres was a more tricky band, the best SWR that could be obtained using the ATU was about 1.5 on this band. No doubt with a bit more experimentation I will find a more suitable length for the radiator wire for the, admittedly compromised, but easy to erect antenna.

If using a twin lead fed doublet antenna then the coaxial cable is plugged in to the other socket so that the Balun configuration is used.

Combined 4:1 Balun and 4:1 Unun by M0MTJ
Combined 4:1 Balun and 4:1 Unun

The Balun/Unun unit is housed in a small plastics case measuring a mere 76mm x 50mm x 28mm. A standard T130-2 toroid core is used with 18 bifilar turns of 18 SWG enamelled copper wire make up the windings in a standard 4:1 balun configuration (see diagram below) wired to the top S0239 socket and the red and green binding posts.

The top socket is used when using the unit as a Balun. A second socket is mounted on the side of the case and is wired for using the unit as an Unun - this is simply connected to the top SO239 socket in 'reverse' - i.e. the centre pin of the top (balun) socket is connected by a short wire link (brown) to the body of the side (unun) socket while the body of the top (balun) socket is connected by a short wire (blue) to the centre pin of the side (unun) socket.

When used with a balanced antenna the twin feeder connects to the two binding posts (red and green) either way around; When used with an unbalanced antenna, such as described above, the radiating wire connects to the red terminal post while the counterpoise or earth wire connects to the green terminal.

4:1 Balun wiring diagram
4:1 Balun wiring diagram
4:1 Unun wiring diagram
4:1 Unun wiring diagram

I am sure purists may frown upon this rather unorthodox home-brew 'lash up', but it seemed like an elegant solution to produce a small, lightweight and dual purpose unit.

Power Handling? I would guess that by using a T130-2 toroid and 18 SWG wire should be adequate for up to about 100 watts power handling, but it is only intended for portable low power use of, perhaps, around 10 watts to 50 watts and so it should handle those levels easily.

* * *

Below is some more information from 2E0KGV, M0UKD, and W4ED which was helpful when working on these little projects:


http://www.sdarc.net/wp-content/uploads/pdfs/Making_Baluns.pdf


4:1 BALUN
4:1 BALUN


4:1 UNUN
4:1 UNUN


9:1 UNUN
9:1 UNUN


1:1 Balun :

1:1 Balun details by M0UKD
1:1 Balun by M0UKD


1:1 Balun by M0UKD
1:1 Balun by M0UKD

1:1 Balun by M0UKD

http://www.m0ukd.com/1to1_HF_Balun_for_dipole/index.php

http://warga11mc.blogspot.com/2010/07/balun-11-14.html



4:1 Current Balun Design by W4ED :
4:1 Balun

W4ED 4:1 Current Balun Design





OTHER PROJECT IDEAS

There are many other useful devices that can be made, such as an ATU for portable QRP use, various types of receivers, pocket sized QRP CW transmitters, complex transceivers - the list is endless. Some projects have to be built from scratch which involves making the necessary PCB, other designs provide a pre-etched PCB while many are available in complete kit form.

Moxon Antennas: I quite fancy having a go at building a Moxon antenna for the SSB portions of 70cm and perhaps another for 2 metres.

Other good projects would be a Noise Bridge or Crystal Calibrator - and more experimental antennas!




Noise Bridge  -  a much lower cost alternative to an expensive antenna analyser

Antenna analysers now tend to be extremely expensive, but a good noise bridge could be used as a much lower cost alternative. A noise bridge can be used for measuring the impedance of antennas and traps at various frequencies. Your H.F receiver is used as the bridge
null detector.

A number a circuits are available on the internet and kits are also available, such as the high quality RX2 from VK3AQZ Kits. Here are some useful links:

LED VU Meter - LM3915 provides 3dB steps
Posted by Jeroen Vreuls

This simple LED VU meter has only a few parts but is useful as an indication of the noise. The circuit is built around a LM3915, the brother of the logarithmic LM3914. The input signal of the VU meter on pin 5 of IC1 put. By pin 9 of IC1 is the display mode sets (bar or dot display). In the situation shown works IC1 in the dot-mode (point). When pin 9 to pin 3 is connected, the IC operates in bar-mode (beam) - the circuit will consume less power in dot mode.
Circuit Diagram
  
http://www.circuitsonline.net
http://www.next.gr  free online electronic circuits






(External Link)  Here's a nice little dual band vhf / uhf antenna project !


(External Link)
Ham Radio 2m / 70cm Vertical Dipole Antenna
Sleeve dipole type for 144 MHz and 430 MHz VHF / UHF


The antenna is by Dave Tadlock, KG0ZZ, and here is a link to his page:  http://www.amateurradio.bz/2m-70cm_vertical_dipole_antenna.html

More great projects from Dave here: http://www.amateurradio.bz/ham_radio_antenna.html







top of page ^


Suppliers of Electronic Components - Bowood Electronics

RSGB - Radio Society Of Great Britain

"One person's junk is another person's treasure"


Links to Electronic Component Suppliers





DISCLAIMER
: If you attempt any of these projects proceed with due caution with regard your
own safety and the safety of the equipment that you are working with!

 
I cannot be held responsible for any accidents, injuries or damage
caused to any equipment that may result.








Mike Smith - MDS975.co.uk © 2003 - 2014





M0MTJ
Subjects covered on this page:
Heil HM-12   Gold Elite  Goldline  HC-4  HC-5  HC5.1  Handi-Mic
Shure PG48 PG58 SM48 SM58; Behringer Ultrvoice XM8500; AKG D5; Audio-Technica VC5; PRO41; ATR1300
Beyerdynamic; Sennheiser.
Using a dynamic stick microphone with the Kenwood TS-590s

Amateur Radio; Ham Radio; Radio; Transceivers; HF; VHF; UHF; Data Modes; Morse Code; RTTY; PSK31; SSTV; FSTV; Amtor; Sitor;
Morse Code; CW; Microphone Adapters; Field Strength; Meter; Yaesu LDG FT Meter; ALC Power Adjustment; Dummy Load;
Antennas; Aerials; Top Band; 160 metres; Cable; Coaxial Cable; Twin Lead; Propagation; Computer; PC; USB Computer Interface; Microphone
Loudspeaker; Filters; Noise Reduction; DSP; Digital Signal Processing.