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RADIO PROJECTS & KITS One of the really fun aspects of amateur radio is making things for yourself. 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 more practical to construct more complex antennas such as Slim Jim or Yagi for example. 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 from a kit of parts bought from Waters & Stanton. You can see this project a little bit further down this page. More recently I built a Field Strength Meter - "FSM"shown further down this page. FUTURE PROJECTS: July 2010: I have been unable operate since March 2010 due to all my equipment being packed away for a house move that has been constantly delayed. I have been having a few ideas as to what homebrew (d.i.y.) projects I want to construct in the near future. The components required for the small electronic projects have already been ordered and delivered in readiness 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. J-Pole Antennas: As far as antennas are concerned I want to build a J-Pole for 10 metres and another dual band J-Pole for 2m / 70cm which has been described by the ARRL. 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. Lightweight Yagi Antennas: However before those projects I really fancy building the ultra lightweight Yagi antennas described by DK7ZB Of particular interest are the 100cm long 4-Element-50Ohm-Yagi for 2 Metres with 7dBd gain; the 5-Element 50Ohm version for 2 metres which is about 1.5 metres long with 8.48dBd gain and the 7-Element 50Ohm Yagi for 70cms with a boom of 100 cm and gain of 10.35dBd. I will also need to install some discrete H.F. antennas in the garden. Once again I'm hoping to be able to use the Inverted L for 40m and 80m and want to experiment with adding elements for 20m and 15m. 10m, I hope, will be taken care of with the J-Pole mentioned above and I also intend to build a trapped dipole for the 12m and 17m WARC bands. Microphone Preamplifier: 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> Power Reducer and Power Measurement for QRP Operation: 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. I am going to make 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 thing screened cable and a project case. When in use the power output will also need to be measured accurately, so.... 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. Analog Meter for Yaesu FT-857D and FT-897D - The Homebrew FT-Meter Yaesu very thoughtfully added an external meter socket to the FT-857 and FT-897 which is excelleint since I like analog S-Meters and 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. The menus of the FT-857 and FT-897 allow the radio to output indications of Signal Strength; Power; SWR; Modulation; Voltage and Discriminator. 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 above. 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 reproducable for this homebrew 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 homebrew FT-Meter for a fraction of the cost of a commercial unit, but Frank has greater image editing and graphics skills 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:  Above: The image graphic for the Yaesu FT-857 and FT-897 meter scale. Save and print if required. When printed, the image will need to be scaled quite 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. Alternatively a bit of simple math's can be used. 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 reulting 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, becuase 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.  Above: The image
graphic for a simple analog S Meter scale.
Save and print if required. 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 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. 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. 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 componets!  Photograph showing the simple construction of the Field Strength Meter  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 resemlence 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 germnium 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 deflecton (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.
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 MORSE CODE PRACTICE OSCILLATOR  Internal view showing PCB and other components  The completed CW Practice Oscillator with Morse Key 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 transciever. 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
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
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)  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  Fitting
the
RJ45
plug
to
the
mic
cable
 Fitting the mic socket on the other end of the 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!! Microphone
preamplifier
ideas
Rather than always using a hand held microphone I would like to experiment with a different microphone that can be suspended from a boom or gooseneck. I have a good quality dynamic microphone and a couple of different unidirectional electret condenser elements to experiment with. The Icom IC-706MK2G is not best suited to dynamic microphones due to their low output, so I decided to look at building a simple external microphone preamplifier to compensate. Building an external amplifier would also allow experiments with some simple audio filtering, particularly useful could be a low pass filter to roll off audio frequencies below a certain point, say below 200 Hz or below 300 hertz, for example. Basic Microphone preamplifier using simple inverting op-amp arrangement:  A Typical Inverting Operational Amplifier configuration The gain is set by R1 and R2. In this case 220,000 Ohms ÷ 2,200 Ohms = gain of 100 x C2 and R1 form a simple first order high pass input filter that would have a gentle filter slope from a cut off frequency of 72 Hertz  fc = 1/(2πRC) Where
f is cut-off frequency in Hertz, R is resistance in Ohms and C
capacitance is
in Farads. (1µF = 0.000001F)
1 ÷ 2 x 3.14 x 2200 Ohms x 0.000001 Farads = 72 Hertz A first order filter will reduce the amplitude of the signal by 6db (power reduces by half) every octave (halving or doubling of frequency) - that is -20dB per decade (factor of 10 of frequency). For SSB communications use a high pass filter with a cut-off frequency of somewhere around 300 Hz might be more appropriate. Changing the resistor R1 to a 5.6k Ohm device and the capacitor C2 to 0.1µF (0.0000001F) would produce an fc of 284 Hertz. Since most capacitors have a tolerance of +/- 20% the 0.1µF capacitor could, in reality, have a value of anywhere between 0.08 and 0.12 µF which would affect the fc quite significantly to between 236 Hertz and 355 Hertz. Switching C2 to 0.22µF would change the fc to 129Hz and switching to 0.47µF would give an fc of 60Hz. Since R1 has been changed, the gain of the amplifier will have also changed. To retain a gain of 100x R2 will need to be adjusted accordingly to 560k Ohms. However a gain of somewhere between 10 and 20 might be more appropriate for connecting a microphone to a transceiver so a value of 100k Ohms could be used for R2 giving a gain of 17 x. The final output level being set by the 1k preset potentiometer being careful not to overdrive the microphone preamplifier in the transceiver. Alternatively, by retaining the 2.2 k Ohm resistor in the above circuit the gain could be set at 21 by changing R2 to 47k Ohms, for example, and the cut off point (fc) could be set to various other values by swapping the capacitor C2 according to fc = 1/(2πRC) : 2.2µF
-
fc = 33Hz
1.0µF - fc = 72Hz 0.47µF - fc = 154Hz 0.22µF - fc = 329Hz + / - tolerance of capacitor and resistor Non-Inverting Operational Amplifier example:  Non-Inverting
Operational
Amplifier
configuration
for
dynamic and electret microphones
www.zen22142.zen.co.uk/Circuits/Audio/lf071_mic.htm Above, a
circuit
design by Andy Collinson for microphone preamplifier of high
quality. The circuit uses a single power supply and is particularly
suitable for dynamic microphones, although electret microphones can
also be used.
The design is a typical non-inverting configuration with input impedance is 23.5k Ohms. The op-amp should be of high quality for best performance with high signal o noise ratio. e.g.TL071, NE5534 or OPA 371 Voltage gain is set by R2 and R1 - use the formula: Vo = ( R2 / R1) + 1 It could also be possible to power the electret element remotely by the addition of a resistor of 1k or 2k from the power supply line to the audio input, but this arrangement needs a DC blocking capacitor at the input - as shown in the above diagram the capacitor is of the incorrect polarity for this function so this would need to be slightly redesigned - a second electret capacitor before the 10µF shown but with reversed polarity should do the job. Care should be taken with values as this will affect the input filtering - a non polarised capacitor might also be considered for this position. Audio Filtering: Rod Elliott of ESP (Elliott Sound Products) provides information in the diagram below for a simple first order input filter when using an operational amplifier in a non inverting configuration. As with the previous example, the cut off frequency, fc, is determined by the formula fc = 1/(2πRC)  Filtering with a
non-inverting operational amplifier arrangement - fc =
1/(2πRC)
Microphone Preamplifier with compressor using the Analog Devices SSM2165-1 integrated circuit:  SSM2165-1 Microphone Preamplifier and Compressor A building block idea that can be modified as explained below The preamp that I intend to construct will
be based around the Analog
Devices SSM2165-1 integrated
circuit along the lines of the circuit diagram sown above which is
based on the DYC817 implementation.
The BC549 transistor is a simple input preamplifier stage. The input level to the SSM2165 integrated circuit being adjusted by the 1k Ohm preset potentiometer. Some designs omit the transistor stage when using electret condenser microphones since these have higher output, however if connecting a dynamic microphone directly to the SSM2165 the internal noise gate may not be successfully opened - causing obvious operational problems! The BC549 stage is therefore included in this design for use with lower output dynamic microphones so that the noise gate within the SSM2165-1 will be opened successfully. The 1k preset potentiometer can be carefully adjusted for proper noise gate operation with both dynamic and electret microphones. The capacitor across pins 3 and 2 couples the internal buffer amplifier to the internal output VCA. The value of this capacitor determines the low frequency response of the unit because it forms a simple high pass filter in conjunction with two 500 Ohm internal resistors - a total of 1000 Ohms; so fc = 1/(2πRC) so; fc = 1 ÷ 6.28 x 1000 x 0.0000033F = 48 Hertz. For voice communications a value of 1µF would provide a roll off below 160 Hertz. A 0.47µF capacitor would produce an fc of 339 Hertz. The compression ratio can be adjusted from 1:1 up to 15:1. The resistor or variable preset potentiometer between pin 6 and ground sets the e compression level. The diagram above allows the resistance to be varied between 47k and 147k which adjusts the compression ratio between 4:1 and 9:1. A value of 5k Ohm or less will produce a compression ratio of 1:1 while using a 200k Ohm variable potentiometer will allow the compression ratio to be adjusted up to 15:1 The capacitors at the input pin 4 and output pin 7 should be non polarised, this helps prevent a 'pop' as the noise gate opens and closes. Adding a 47k Ohm resistor in parallel with a 22µF capacitor from pin 5 to ground will also help to eliminate the 'pop' from the noise gate as it opens and closes by smoothing the attack and release curve, reducing the attack and release time constant. The SSM2165 datasheet suggests that a 22µF would be suitable for music use, but during speech communications one would always hear a noticeable rise in audio level during a pause in speech for an additional one or two seconds before the noisegate closes - a very annoying effect for the receiving station. The use of a 22µF in conjunction with a parallel 47k Ohm resistor will cause the noisegate to close immediately after the speech stops of during a short break in speech. (Tip by DG2IAQ ) The capacitor from pin 5 to ground controls the time constant of the internal level detector, values of between 2.2µF and 22µF can be used and will change the response to low frequency sounds. According to the data sheet 'Capacitor values from 18µF to 22µF have been found to be more appropriate in voice band applications, where capacitors on the low end of the range seem more appropriate for music program material. For optimal low frequency operation of the level detector down to 10 Hz, the value of the capacitor should be around 22µF. Some experimentation with larger values for this AVG CAP may be necessary to reduce the effects of excessive low frequency ambient background noise. The value of the averaging capacitor affects sound quality: too small a value for this capacitor may cause a “pumping effect” for some signals, while too large a value can result in slow response times to signal dynamics'. OTHER PROJECTS 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. Another project that I wish to make in the future is a Noise Bridge. I even fancy having a go at a Crystal Calibrator - and more experimental antennas - of course! Looks like my soldering iron may
be busy!
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Mike Smith - MDS975.co.uk © 2003 - 2010
M0MTJ
Subjects covered on this page:
Amateur Radio; Ham Radio; Radio; Transceivers; HF; VHF; UHF; Data Modes; Morse Code; RTTY; PSK31; SSTV; FSTV; Amtor; Sitor
Antennas; Aerials; Cable; Coaxial Cable; Twin Lead; Masts; Poles; Propagation; Computer; PC; USB Computer Interface; Microphone
Loudspeaker; Filters; Noise Reuction; DSP; Digital Signal Processing; Morse Key; SWR ; Inverted L; Inverted V; Dipole; Doublet;