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AERIALS (ANTENNAS) 6

Index To Other Antenna Pages:
Antennas 1 : Aerials used by M0MTJ
Antennas 2 : Including ideas for compact antennas for Top Band /160 metres
Antennas 3 : Felix Scerri VK4FUQ discusses Loop Antennas, baluns, masts & other antenna related topics
Antennas 4 : Many antenna ideas from various sources particularly for multi-band operation & also gives information about
antenna trimming,   knots for wire antennas and useful antenna rigging accessory ideas.
Antennas 5 : Half Wave End Fed antennas for 144 MHz VHF / 430 MHz UHF and 50 MHz 6 Metre band  & J-Pole Aerials
Antennas 6 : Simple and effective H.F. Antenna ideas - Ground Plane  and  All Band Doublet
Antennas 7 : Omni-Directional - Circularly (Mixed) Polarized Antenna for VHF / 2 Meters.
 

"Everything should be made as simple as possible, but not simpler."  -  Albert Einstein


The All Band Doublet Antenna - An Efficient Multi-Band Aerial - (Dipole fed with Balanced Line (Not Coax !))

In 2014 I installed a newly constructed Doublet Antenna. The top wires are 20 metres in total length - perfect for the 40 Meter Band, but because it is fed with balanced line /  ladder line back to the antenna matching unit (ATU) it will work very efficiently on most bands between 40 Meters to 6 Meters. It even works pretty well on 80 metres. The 'old timers' were right - use a Doublet: If you want an efficient all band antenna that is easy and cheap to make that should be quite easy to accommodate and install.....

If you are a QRP station or a limited to 10 watts - make the most of every last drop of your precious transmitter power and install the most efficient antenna you can, Install a Doublet and feed it with lowest loss open wire line or ladder line feeder.

Don't spend a fortune - build a Doublet Antenna!

M0MTJ
                              All Band Doublet Antenna
MØMTJ All Band Doublet Antenna
A Doublet Antenna is fed with balanced line - Not Coax!
(part of antenna shown)


Main Benefits of a Doublet as a true Multi-Band Aerial    -    Perhaps your ideal single, multi-band antenna

A Doublet can be used on whatever frequency it is cut for, and higher frequencies. Usefully, there can be some useful gain on higher frequencies, although there will be some petal shaped lobes on the higher frequency bands.

Balanced ladder line or open wire balanced feeder must be used (NOT coaxial cable). Ladder-line or open wire line ensures lowest loss at High Frequencies so that as much of your precious transmitter power as possible will be radiated by the aerial itself an not lost as heat in a coaxial cable. Likewise receive efficiency should be maximized. Assuming that the aerial is successfully balanced, the feeder should not radiate, even when there is (inevitably) high SWR.

For those operators coming from CB, high SWR is not necessarily a bad thing, it's just the way you handle it that matters.  Use good quality low loss feeder (ie not coaxial cable) and proper impedance transformation and matching, and antenna system efficiency will be maximised. 

So, high SWR is not an especially bad thing and will not reduce the aerial's performance, but do note that high SWR on the balanced feeder does increase feeder loss compared to a when matched - but the losses will be a lot less significant then if coaxial cable were to be used. This ensures that efficiency should be better so that all the power that reaches the antenna wires will be radiated - save for any losses in the antenna tuning unit (AMU) or the balanced feeder cable. 

Remember:

Balanced Line = Lower Loss  =  More Power Transmitted = More Signal Received

Balanced Line = Less Noise On Receive  (coaxial cable can suffer common mode currents, particularly on un-balanced aerials, that increases noise from local QRM, but if properly installed and balanced, open wire balanced line feeders can exhibit lower noise on receive while also increasing received signal strengths too).


Feeder Types

Use open wire line if possible for lowest loss. This can be any convenient spacing, such as 2inch (25mm) 3 inch (75mm) or 4 inch (100mm) and can be made up using 'home brew' or commercially available ladder line spacers.  Alternatively the standard commercial 300 Ohm or 450 Ohm ladder line feeder could be used.


Description

The All Band Doublet can be a very good all-round antenna with particularly good performance on the band that it is cut for - in this case the 40 Meter Band where it acts as a Half Wave Dipole. However, if you have the space, cut it for the lowest possible band.

    Approximate half wavelengths would therefore be: 40 Metre Band: 21 metres;  80 Metre Band: 42 metres;  160 Metre Band: 81 metres

If you don't have the horizontal space to install an aerial cut for half wave at the lowest frequency, it's perfectly feasible that a 3/8th wavelength top wire could be used instead and probably still be about 95 to 98% efficient. The matching may be a little more difficult however.

    Approximate 3/8th wavelengths would therefore be: 40 Metre Band: 16 metres;  80 Metre Band: 32 metres;  160 Metre Band: 60 metres.

The Doublet (a Balanced Dipole) is not fed with coaxial cable, instead Balanced Open Wire Line; Ladder Line or Balanced Twin Feeder must be used. I chose 300 Ohm Ladder Line for my first Doublet aerial, but 450 ladder line could also be used. I later experimented with wide spaced home constructed balanced open wire ladder line which works very well.

Coaxial cable must not be used for this antenna due to that fact that on many bands the SWR will be very high and losses in coaxial cable will become unacceptably high with consequentially large losses of transmitted power and large losses in received signal strength. The longer the run of coax, the larger the losses will become. Therefore open wire feeder or ladder line must be used to feed the aerial into a Balanced Matching Unit ("ATU") or a standard Antenna Matching Unit ("ATU") via a high quality low loss current balun.

When using 300 Ohm or 450 Ohm ladder line, or open wire line, it should be installed so that it does not run near metallic objects (pipes, cables, wires, metal window frames etc) otherwise the balance will be disturbed, thereby negating its benefits - i.e. it will become Un-balanced with the RX interference and TX EMC problems that that implies.

[N.B: Spectrum Communications sell 100 Ohm Twin Feeder which is easier to work with than typical 300 Ohm or 450 Ohm Ladder Line because it is not so sensitive to its surroundings. However, this 100 Ohm feeder will have much higher losses than 450 Ladder Line and more particularly wide spaced open wire line, so the penalty for convenience will be significantly increased overall losses. http://www.spectrumcomms.co.uk ]

When using balance feeders, either a balanced Antenna Matching Unit ("ATU") or an 'ATU' with a good, low loss BalUn at its input will be required. A 1:1 Current Balun would be ideal but try a good low loss 4:1 Current Balun if you have one. A 1:1 current balun may work better.

The aerial can be designed for use from 160 through to 10 meters very easily using the standard 1/2 wave dipole formula. However, the exact length is not critical, you can try simply cutting the two top wire to be simply as long as long as your space allows. Ideally a minimum of 3/8th wavelength at the lowest frequency of operation, but perhaps more ideally a half wavelength at the lowest frequency of operation.

Installing the antenna as an upside down vee (Inverted V) with a central support will mean that the antenna takes up less horizontal space than if it were installed as a flat top aerial. An Inverted V may also have an advantage of being slightly less directional than a Flap Top aerial.

A Note About Baluns - I used a 4:1 ratio Guanella Current Balun for my original design, and this is often recommended by other users. However, it may be better to use a 1:1 Current Balun.

A 1:1 current balun should have lower losses and be more efficient, so that the aerial system radiates more effective power. Additionally a 1:1 current balun may present a more easily matched load to the matching unit ("ATU") - this is because, for example, if the antenna presents a very low impedance at a certain frequency or frequencies, the 4:1 transformation ratio will make that impedance even lower (even worse) and might be impossible to match for some matching units.

Steve G3TXQ has an excellent article explaining why the use of a 1:1 current balun would be preferable:
Amateur Radio (G3TXQ) - Tuner Balun: 4:1 or 1:1 ?  http://www.karinya.net/g3txq/tuner_balun/

Whatever type of balun and whatever the overall length of the aerial top-wire, if you have difficulty in matching some bands, try adjusting the feed line length, by adding, or removing a Metre or two.

Note also that the internal "ATU" found in transceivers will be entirely unsuitable to use for this type of aerial. You will need a good external matching unit, either manual or automatic that can match at least  10:1 SWR or better.  Internal transceiver "ATUs" can only match 2.5:1 or 3:1.  There are some MFJ "ATU's" that can match a very wide range, - for example the MFJ MFJ-993BRT, MFJ-939Y and MFJ-929 can match a range of 6 to 1600 Ohms (an SWR up to 32:1). I have not tried these yet, but I am keen to take a look.  At the moment (Dec 2017) I use an MFJ 949E manual tuner which seems to be able to match almost anything.

Examples: The All Band (Balanced) Doublet Antenna cut for 20 meters will have an overall length about 10 metres i.e a 1/2 wavelength on the 20 Meter Band. With a good balun and 'ATU' this antenna should cover 20 metres to 6 metres.

The 20 to 10 Metre Band Doublet : 300 ÷ 14.175 MHz = 21.16 metres  ÷  2  =  10.58 less 5% =  10.05 metres - Therefore each leg will be about 5 metres long.

For an 80 to 10 Metre Band Doublet : 300 ÷ 3.65 MHz = 82.19 metres  ÷  2  =  41.09 less 5% =  39.04 metres - Therefore each leg will be about 19.5 metres long.


My 40m to 6m Doublet Antenna:

300 ÷ 7.00 MHz = 42.85 metres  ÷  2  =  21.42 less 5% =  20.35 metres - Therefore each leg will be about 10.2 meters long.

The overall length is therefore about 20 metres long - a 1/2 wavelength on the 40 Meter Band. With a good GWhip balun and and LDG 'ATU' my antenna covers 40 metres, 20m, 17m, 15m, 12m, and 6 metres. 10 metres presents a problem because the ATU will not match to a low enough SWR, however this could be improved or cured by trimming the balanced feeder cable. Please refer to "Trimming The Feedline Length" below.

I have also found that the aerial puts out a creditable signal on 80 metres for inter-G despite its relatively small dimensions for the band and the fact that it is only 7 meters above ground level.


Height Above Ground

A horizontal aerial that is installed at 3/4 of a wavelength above ground will have a radiation angle of about 20 degrees which is good for DX. When the height above ground is only 1/2 a wavelength the radiation angle increases to about 40 degrees. For low horizontal aerials that are only about 1/4 above ground level the radiation angle is higher still so much of transmitted energy goes upwards - "NVIS" - which will reduce DX possibilities, but may prove good for local contacts - "Inter G" - this is caused by the radio waves being reflected upwards from the ground when an aerial is installed at low heights compared to the wavelength in use.


Construction:

Building a home brew Doublet Antenna could not be easier. First, here is a list of the components that will be needed.

Components Required:

Most 'seasoned' Radio Amateurs will already have most of the necessary materials in the 'junk box' but here's a list anyway:

Antenna Wire:
  Suitably strong wires such as the antenna wires from W H Westlake or Spiderbeam CQ-532 antenna wire or
Aramid / Kevlar antenna wire from Nevada

Dipole Centre
This can be home brewed from suitable insulation material or be a commercial item e.g. from W H Westlake
End Insulators for the end of each dipole 'leg'
These can be home-brewed of commercially bought 'dogbone' or 'egg' insulators from W H Westlake
Feeder
This can be home constructed Open Wire Line for lowest losses, e.g. using 85mm open wire spacers (Wimo 30025),
or 300 Ohm or 450 Ohm Ladder Line available from W H Westlake

Ring Terminals
To terminate the ends of the feeder and antenna wire
Self Amalgamating Tape
To wrap around joints protecting from weather - available from W H Westlake
Liquid Electrical Tape
Available from SOTABeams - excellent for ensuring that all the joints really are waterproof
Support Rope
I use strong high quality Maastrant Cord, but other high quality UV stabilized rope or cord could be used
Pulleys
Pulleys used to run the support rope through at each end so that the antenna can be easily raised and lowered

Can be obtained from chandlery suppliers or search ebay for "stainless steel pulley"
Support Poles
Fibreglass or wood poles or existing structures (pole fixed to house, pole in garden or tree etc)
Stake
Strong stake to support the pole. I used a metal 'MetPost' to hold a 2 metre long wooden post with the fibreglass pole fixed to this.
Cleats
Two cleats; to tie each end of the support ropes
Current Balun
  Use a high quality low loss 1:1 current balun, but if you have a good low loss 4:1 current balun, try that.
ATU
I have used an LDG Z11 Pro but consider the MFJ-993BRT, MFJ-939Y or MFJ-929 which can match much wider impedance
ranges of between 6 to 1600 Ohms (an SWR up to 32:1).
IP Rated Enclosure
A dust and weather resistant box to protect the remotely located automatic ATU


Antenna Parts Suppliers : W H Westlake / Sandpiper Aerial Technology / G-Whip Antenna Products / Nevada Radio / Wimo / Radioworld UK

Spiderbeam CQ-532 antenna wire (AWG 18) very strong and durable multistrand Copperweld
Very strong and durable antenna wire. Multistrand copper-clad steel wire combines the mechanical
strength of steel wire with the excellent conductivity of copper. It does not stretch at all & has very good HF properties (low losses).
Original "Wireman" CQ-532 multistrand Copperweld silky wire, black PE insulation, UV resistant multi-strand
wire diameter = 1.1mm (AWG 18)
outer diameter (including PE insulation) = 2.2mm
breaking strength = 50kg
weight = 10g/m
http://www.spiderbeam.com

Planning Your Antenna Installation

Decide on the lowest frequency on which you need to operate and then cut the top wires accordingly, but make them about 1 meter longer than calculated to allow for connection at the dipole centre (T piece) and also for tuning adjustment if necessary. Attach a 'dogbone' or 'egg' insulator to the ends of each leg. The extra length is simply folded back on itself at each end.

Attach an appropriate length of support rope to each end insulator, ensuring that it will be long enough to let the aerial down and still ties off securely to the cleats if necessary in the future.

Connect the wires to the ladder line using the dipole centre 'T' piece and seal all joints with self amalgamating tape and / or liquid electrical tape to ensure that it is waterproof. The aerial can now be hoisted into position. The position can be as a traditional 'Flat Top' supported at each end or as an 'Inverted V' with the T piece supported at the centre:

Flat Top: Each end is supported by a pole, tree or a support pole on the house, with the feeder dropping down vertically from the centre.

'Inverted Vee' : The centre feed point supported by one pole, as high as possible, leaving the two arms sloping back down towards the ground. This method will need less horizontal space than the flat top version. The ends should not touch the ground and ideally should be several feet above it. If the support pole is metal the twin feeder or ladder line will need to be spaced several inches from it to avoid the feeder becoming unbalanced which would induce unwanted losses and RFI problems. It may be easier to use a non metallic pole such as wood, or ideally strong fibreglass poles. I use Tecadi poles.

I installed my doublet as a 'flat top', however because I had not quite got the full 20 meter length required for the full length of the antenna, a few meters of one wire leg at the far end of the aerial are vertically run down the fibreglass support pole at the bottom of the garden. (If you haven't quite got enough space the antenna can certainly be installed as an upside down U, with each end dropping down a few metres).

From the centre feed-point of my doublet, the ladder line drops down roughly vertically into a garden cabinet ('ATU Building'). The feeder is connected to the GWhip current balun which is itself then connected to the LDG antenna matching unit via a very short RG213 patch lead (about 60cm long).

Now that the ATU has matched the impedance to 50 Ohms, coaxial cable can be used to feed back to the radio in the shack with minimal losses. Therefore from the ATU in the shed, I ran a length of RG213 coaxial cable back to the radio.

For best results a doublet should be mounted as high as possible, as is the case with most aerials. As noted, the aerial can be erected as a flat top or an Inverted Vee.


Trimming The Feedline Length

Depending upon the matching range of the particular ATU and balun combination, it may not be possible to achieve a match on all bands due to the SWR being too high and outside the matching range. Since the high SWR points will repeat at half wavelength intervals along the feeder, it should be possible to correct a certain difficult band by trimming (or extending) the length of the feeder. Try making adjustments at 0.1 wavelength at a time for the band that is causing a problem.

W8JI notes : "The optimum length for a multiband dipole is near 1/2 wl on the LOWEST band, and the optimum open-wire feedline length is any odd multiple of 1/8th wavelength on the lowest band. This means an optimum 80-meter dipole would be about 125ft long, and the feedline would be 25-30ft, 75-90ft, or 125-150ft long. The longer the feeder, the more likely you are to having to trim it for optimum tuner performance".http://www.w8ji.com/short_dipoles_and_problems.htm

M0MTJ All Band Doublet Antenna
MØMTJ All Band Doublet Antenna

M0MTJ All Band Doublet Antenna
MØMTJ All Band Doublet Antenna
Detailing the Dipole Centre "T" Piece and 300 Ohm Ladder Line

(2015 Update: I now use 80mm spaced 'home-brew' Open Wire Line and have added a
second 'fan dipole' element for better matching on 10m and 6m.)


M0MTJ Doublet Antenna
Above: Diagram of the M0MTJ Doublet Antenna
The Automatic ATU is protected inside an IP Rated enclosure.
The IP rated enclosure and the Current Balun are inside the "ATU Building".



The Improved All Band Doublet Antenna

As mentioned above, it may not be possible to achieve a match on all bands due to the SWR being too high and outside the matching range of the automatic antenna matching unit. The standard practice would be to trim the feed-line slightly, as described.  However an alternative method, if one of the shorter wavelength bands did not match, could be to add a second dipole element for the band affected. This might be described as a Fan Dipole element.

I found that my Doublet antenna, with the 4:1 G-Whip current balun and the LDG Z11-Pro antenna matching unit, would match on all bands from 80metres to 6metres with the exception of 10 metres. Rather than immediately trimming the feeder, I thought that it would be very interesting to add a second dipole element for the 10 metre band. Each leg of this second element is about 2.5 metres long and is simply connected to the centre T piece in the usual way. The wires are held in place, under the main doublet top wires, with ladder 80mm line spacers (WS-2580  or Wimo 30025). The end of the wire of each arm dangles down freely by about 20 centimeters.

Once in place, I trimmed the ends of the 10 meter-band dipole wires until a good match was obtained across the whole of the band.

Brilliant!  However, there was a problem: It was not then possible to achieve a match across the whole of 6 meters.

My immediate idea was to create a virtual dipole for the 6 metre band by adding a "tail" at the 50 MHz quarter wave point on each of the 10 metre dipole arms. Each "tail" is simply a loop of wire pulled out of each of the 10 meter dipole arms and twisted up to form a single wire that dangles down, about 20cm in length. The position of each tail is about 1.4 meters out from the centre.

With these refinements in place, it was then possible to obtain a match on every band from 80 meters to 6 metres.

The advantages of using this additional element ("fan dipole" arrangement) are, I believe, greater efficiency on 10 meters and 6 metres due to better matching and perhaps more significantly, that the radiation pattern will be a more predictable dipole figure of eight pattern, rather than breaking up into lobes as happens when using higher frequencies on a long wavelength aerial.

Worth a try! 

Here's the updated diagram. I am now using open wire balanced feeder made from 80mm ladder line spacers / spreaders (WS-2580  or Wimo 30025):

M0MTJ_improved_Doublet_Antenna
The Improved Doublet Antenna with added Fan Dipole element for 6 Metres and 10 Metres
(August 2015)

M0MTJ_Doublet_Antenna

M0MTJ_Doublet_Antenna

M0MTJ_Doublet_Antenna
M0MTJ Doublet Antenna showing centre piece and 80mm ladder line spacer / spreader


GWhip 4:1 Guanella Current Balun
GWhip Current Balun
http://gwhip.co.uk/baluns/current/


LDG Automatic Antenna Matching Unit
LDG Automatic Antenna Matching Unit
http://www.ldgelectronics.com/


See the diagram below and visit the link for much more information from other websites: 

All Band Doublet -
                                  http://www.hamuniverse.com
All Band Doublet - http://www.hamuniverse.com/hfdoublet.html
The All Band Doublet antenna is nothing more than a 1/2 wave dipole cut for your lowest operating frequency and fed with ladder line or
balanced open wire, etc to a tuner that will accept a balanced line connection. IT IS NOT FED WITH COAX!

4 Dollar Special by W1GFH
4 Dollar Special by W1GFH
http://www.qsl.net/wb1gfh/antenna.html



More useful information here:  Introducing The All Band Doublet by the late L.B. Cebik W4RNL:  http://www.cebik.com/content/edu/edu6.html
N.B. Create a free account at  http://www.cebik.com 

Also find the article Introducing The All Band Doublet by L.B. Cebik W4RNL here:
http://ftp.unpad.ac.id/orari/library/library-sw-hw/amateur-radio/ant/docs/Introducing%20the%20All-Band%20Doublet.htm



BBC Radio Shropshire - Jim Hawkins talks to me about Amateur Radio and the Doublet Antenna:

BBC Radio ShropshireJim invited a discussion on things that listeners had built, either from scratch or from a kit. I emailed my stories of building various projects and antennas to Jim and he rang me back. Here's a recording of the short conversation about the magic of radio communication on BBC Radio Shropshire on July 14th 2015:

PLAY> Listen to the Audio - Jim Hawkins talks to Mike Smith MØMTJ about Amateur Radio on BBC Radio Shropshire





All Band Sloper Antenna for 160 Meters (Top Band) to 10 Meters

On my visit to the National Hamfest in 2014 I bought a new CG Antennas CG-3000 Remote Automatic Antenna Coupler.

The CG3000

Although the unit is weatherproof and designed to be used outside, I decided to install it inside a dedicated IP56 rated electrical junction box enclosure, to prevent rain falling directly on to the CG-3000.

The CG-3000 unit is described as being an affordable and easy solution for you to construct a full band antenna. It covers all amateur bands from 1.8 MHz to 30 MHz continuously.

An antenna wire as short as 8 meters can be used - though it won't be very efficient or effective on the longer wavelength bands - so use as long a wire as possible.

The CG3000 can feed a 'long wire', mobile whip, vertical antenna or dipole antenna (without balun), etc. Power handing is 200W PEP, it is quick and easy to 'tune' using 200 memory channels. The casing is solid, robust and waterproof, and compact in size and light in weight.
CG-3000 remote
                              automatic antenna coupler

Installation

I installed the CG3000 unit onto a short, treated, wooden post at the bottom of the garden. The post also supports a short, telescopic fibreglass pole - the total height is around 3.5 metres.

As mentioned above, I took the additional precaution of fitting the CG3000 inside an IP56 rated (dust and water resistant enclosure). The enclosure measures 380mm x 300mm x 120mm. I obtained it from A1 Electrics on ebay.

I fitted waterproof glands to the bottom of the enclosure to feed the RG213 coaxial cable, power/remote control cable and the earth wire to the CG3000. On the top of the enclosure I fitted a stainless steel machine screw, nut and wing nut, connected via a very short, thick wire to the CG3000's antenna connection. The antenna wire would be connected to this.

The RG213 coaxial cable and the power/remote control cable run around the edge of garden back to the 'shack'. The earth cable is kept as short as possible and connects to an earth rod directly below the CG3000. Additional counterpoise wires run around the garden.
IP56 rated
                              enclosure

My Antenna Wire

Initially I installed a single 20 meter long sloping wire. This ran vertically up the 3.5m tall fibreglass pole, then ran back, sloping upwards, to a fixing point on a short pole mounted on the side of the house, using a small 'egg' insulator, Paracord lanyard and pulley, as shown in the diagram below.

The CG-3000 could tune most bands in this configuration except 40 Meters. This is due to the fact that the 20 metre wire length is half a wavelength long on the 40 Meter Band, so the impedance at the end of the wire would obviously be very high - too high an impedance in fact for an automatic antenna coupler to transform.

The solution seemed simple. I decided to add an additional parallel wire of 10 meters in length. This would present a lower impedance at the end feed-point on the 40 metre band. I attached the second 10 metre long wire to the 20 meter wire using 80mm ladder line spacers, as shown in the diagram below, so that the two wires run in parallel.

With the two wires in place, the aerial system is now able to be used on all bands from 160 meters (Top Band) to 10 metres. The CG-3000 is working well. The simple remote control unit is very useful.

M0MTJ_Sloper_Antenna_for_160_m_to_10_metres
M0MTJ Sloper Antenna using two sloping wires, one 20 meters in length and another parallel wire of 10 metres in length.
The aerial wires are fed at the far end of the garden via a CG Antennas CG-3000 Remote Automatic Antenna Coupler.
The CG-3000 coupler is fed back to the shack using RG213 coaxial cable (not shown).

The Sloper Aerial definitely radiates, as can be seen from a selection of my WSPR maps and logs for various bands below:

M0MTJ__WSPR_logs_pages
160 metres (Top Band) spots using a transmitter power of 5 Watts in WSPR mode
See my WSPR page here and logs and maps page here

CG-3000 remote automatic antenna
                              coupler
The CG Antenna  model CG-3000 remote automatic antenna coupler,
shown as supplied by Martin Lynch and Son with the remote control unit.
CG3000 from Martin Lynch and Sons
ML&S - http://www.hamradio.co.uk/


The CG Antennas web page explains: "The CG-3000 is designed with Pi matching network. It provides more wide tuning range and covers whole HF band. Using 9 solid inductors, the total inductance ranges from 0 to 32 uH. They can give 255 combinations with a resolution of 0.25 uH. 5 capacitors are used at the input side, the total capacitance ranges from 0 to 6300 pF with 31 combinations. Other 5 capacitors are used at the output side, the total capacitance ranges from 0 to 755 pF with 31 combinations. So totally they give 245055 tuning combinations"CG-3000 User Manual

Specifications
Tunable frequency: 1.8 - 30 MHz with long wire antenna from 8 meters
Input impedence: 45-55 ohms
Input power: 10 - 200W PEP
SWR: <2:1
Power supply voltage: 12V +/- 10%
Current consumption: <0.8A
Auto tuning time:

Approx. 2 seconds (first time tuning)Less than 1 second (return to memory frequency)

Memory channels: 200
Weight: 1.8 KG
Size: 310mm X 240mm X 72mm (L - W - H)

 CG-3000 remote automatic antenna
                                coupler

The CG Antenna  model CG-3000 remote automatic antenna coupler
http://www.cgantenna.com/cg3000.html




Simple HF Antennas

After some enquiries regarding different types of antennas from M6IAH and M6CQC and a complaint of noise on his Off Centre Fed Dipole from M6CQC, I suggested investigating the use of a "Choke Balun" to reduce common mode currents that may be causing noise on the OCFD antenna and also "home brewing" a couple of alternative antennas that may have different and perhaps better performance - hopefully a lot better than the 27MHz Antron 99 CB antenna that had also been pressed into service on the 20 metre band.

First, a couple of antennas that are very effective, very simple to 'home brew' and extremely cheap:


Simple 1/4 Wave Ground Plane Antenna for 20 Metres


Although these details and my (very) rough sketch below describe a 1/4 Wave Ground Plane Antenna for the 20 Metre band, the formula shown can be used to produce an antenna for 10 metres, 12 metres, 15 metres, 17 metres, 30 metres or even 40 metres given a long enough fibreglass fishing pole or support.

If a fishing pole is used as the support it must be fibre-glass rather than carbon fibre as carbon fibre is an electrically conductive material which will degrade the antenna's performance.

My rough drawing of the simple but effective 1/4 Wave Ground Plane Antenna shows the radiator wire and the radial ground planes are all 1/4 wavelength long.

Simple 1/4 Wave Ground Plane Antenna
Simple 1/4 Wave Ground Plane Antenna
Ideally the 4 radial wires should slope down at an angle of 45 degrees from horizontal


Wavelength is calculated thus:

Speed of Light ÷ Frequency in Hertz = Wavelength in Metres.

Centre of 20 metre band is 14,175,000 Hertz

So:  300,000,000 ÷ 14,175,000 = 21.614 metres

Or, for a simpler calculation use this method:  300 ÷ Frequency in MHz  i.e.  300 ÷ 14.175 MHz = 21.614 metres

So: 21.614 metres ÷ 4  =  5.29 metres  =  Quarter wavelength at 14.175 kHz


My rule of thumb is that you can reduce that length by about 5% - that would be 5.02 metres for the radiator wire, but the effect on velocity factor that the fibreglass support has on the antenna could reduce this length further.


Construction

The vertical support is an inexpensive fibreglass telescopic fishing pole. I have shown a 10 metre pole in the diagram, but a shorter 7 metre one could be used if limiting height is a consideration.

Cut the radial wires to about 5.2 metres each - they should all be equal length.

Start with the vertical radiator wire rather longer than necessary - say 5.5 metres.

Then, using an SWR meter or antenna analyzer, find the frequency that has the lowest SWR. This point of minimum SWR will no doubt be found at a lower frequency than the bottom of the 20 metre band (i.e. lower than 14.0 MHz) - that's because the wire radiator is too long, so its wavelength is too long and therefore its frequency too low. Next, trim it little by little until the lowest SWR is in the centre of the 20 metre band at about 14.175 MHz.

All measurements should be made with the wire fixed in its final position on the support otherwise the SWR readings will be misleading. 

The radial wires should not be trimmed.

NOTE: Ideally the radial wires should droop away from the feed point at an angle of 45 degrees from horizontal - this ensures that the feed-point impedance will be around 50 Ohms, which is what is required by the 50 Ohm coaxial cable and the transceiver. However this angle may be less if using a shorter support pole.

One method of feeding the antenna and connecting the radial wires and the vertical radiator:

Simple
                              1/4 Wave Ground Plane Antenna
A temporary feed-point arrangement of the simple 1/4 Wave Ground Plane Antenna
For a permanent installation this should be housed in a weather proof enclosure.
The coaxial cable's PL259 plug and SO239 socket should be protected with self amalgamating tape.

It may also be wise to connect a 470,000 Ohm Static Bleed Resistor from the radiator to ground (the radials)
and ground the coaxial feeder to an earth stake. 

Ideally the 4 radial wires should slope down at an angle of 45 degrees from horizontal



The four radial wires can be soldered to the four corner holes of an SO239 chassis socket, or have a terminal lug soldered on to the end of each wire, and then the lugs fixed to the chassis socket using small stainless steel machine screws. For a permanent installation everything should be weather-proofed.

Depending on the angle of the ground plane wires, the feed-point impedance should be somewhere between 48 Ohms and 72 Ohms at resonance, a reasonable enough match. Ideally a coaxial choke (15 turns of RG58 coaxial cable on a 50mm PVC pipe) or a few clamp on ferrites should be included at the feed-point on the coaxial cable. 

The antenna is fed with the 50 Ohm coaxial cable back to the shack. If the bandwidth proves to be wide enough the whole of the band may be usable without an Antenna Matching Unit ("A.T.U."). If designed for other bands such as the narrower 30m, 17m or 12m band the bandwidth will almost certainly be sufficient to use without an antenna matching unit.


Antenna Wire

For antenna experiments, get a big reel of  "PVC COATED AERIAL WIRE….Medium..about 16 /18 swg…PRICE..18p per Metre"   from W H Westlake:

http://g4cqm.www.idnet.com/westlake-pdf/cable-wire.pdf

http://www.whwestlake.co.uk/




USEFUL KNOTS FOR ANTENNAS
Bowline Knot as shown on
                              http://www.radioworks.com
The Bowline Knot


NOISE and Unbalanced antennas

Unbalanced antennas and feeders can often be subject to "Common Mode" currents - essentially unequal currents flowing down the coaxial cable on the outside of the feeder. Common Mode problems will cause more noise on receive than would otherwise be the case, and also be potentially problematical when transmitting - causing nearby equipment to suffer interference or EMC problems - (Lines on TV and computer screens, blocking of TV signals, picture break up, noise coming through nearby radio or audio equipment, or causing PC's to crash, for example)

With so many electronic gadgets in use, the potential for receiving large amounts of locally produced QRM (man made radio interference) can pose real problems causing sometimes impossibly high noise levels. Just think about all those switch mode power supplies for all the nearby iPads, MP3 players, iPhones, iPods, XBoxes, Laptops, PC's Rechargable shavers and toothbrushes, TV's, especially 'plasmas' all spewing out wide band noise!

If excessive noise pick-up is caused by common mode issues then the use of an effective choke can help improve matters:

Half a dozen clip on ferrite rings ( http://www.nevadaradio.co.uk/amateur-radio/rf-filters/?page=2 ) could be put on to the coaxial antenna feeder cable, in a tight row, near the feed-point of the antenna, Or...

Build the "Ugly Balun" - It's not a "Balun" at all. It is simply a "choke".  If enough turns of coaxial cable are wound around a cylindrical former (e.g. a short length of PVC drain pipe) then there will be enough Impedance to radio frequencies above a certain frequency to 'Choke Off' the common mode currents that would otherwise flow down the outside of the coaxial cable causing unwanted noise and possible EMC issues.

Here is a good article:  http://www.hamuniverse.com/balun.html











Mike Smith - MDS975.co.uk © 2003 - 2018





M0MTJ
 
Amateur Radio; Ham Radio; Radio; Ground Plane Vertical; Sloper; HF Antenna; Dipole;
Doublet; Antenna - The Best Multi-Band Antenna for Easiest Construction, Quickest Deployment and Lowest Cost