A talk given by Martin M0GQB to club members on 5th November 2014
About a year ago, I gave a series of short presentations based on the question "How do I ..." with one topic a week. One question asked but not answered at the time was "How can I erect a top band aerial in my garden?" The reply merited a longer discussion than the time would have allowed so I re-formatted the reply as a longer talk which I gave during a club meeting.
As a prelude to answering this question, I would like to recount my efforts in erecting an aerial in my garden so that I could take part in the RSGB 80m Club Contest. Some of the decision-making process should be applicable to anyone considering erecting a top band or 80m aerial in a small garden.
I live in a house which was built around 1600 and is the middle part of a much bigger building. Like any terrace house, this means that I don't have any gable ends to erect poles or easy access from front to back. In addition, I don't have a chimney stack on our roof – the stacks are actually in our neighbour's roof. Because the building is so old, I don't want to erect a permanent aerial. Not only would a modern aerial look totally out of place but, because the building is a Grade II listed building, I am fairly sure that the council would object to my plans.
In addition, when the house was built, such matters as making the garden long enough to take a top band aerial didn't occur to the builders. The house is relatively close to the road and I have therefore a fairly short front garden as well as an even shorter back garden. The longest length I can get in a straight line is about 13m diagonally across the garden and this line is orientated slightly north-north-west to south-south-east. To complicate matters, the house is built into a slight slope so that the access road at the rear is about 20 feet higher than the road at the front. Fortunately, the front garden has been levelled somewhat which makes it about six feet above the road but there is still a small step in the slope near the house.
These natural and self-imposed limitations have given me several problems when considering an aerial for 80m.
So what was I wanting? I wanted an aerial which: would cover the frequencies used in the RSGB 80m Club Contest – that's 3.600 – 3.650 MHz and 3.700 – 3.775 MHz – preferably without using a tuning unit; would fit in the space I had available; was easy and quick to put up; was easy to store; and would be efficient so that I had a chance of making at least some QSOs in the contest. I wasn't after DX, or long-distance QSOs, so the radiation pattern of the aerial was significant. My concern was to get out with a signal and maximise the number of contacts I could make in the UK for the Club Contest so I wanted short- to medium-range skip. In other words, I wanted to be able to get nearby QSOs as well as medium distance to about 500 or 600 miles.
As an extra requirement, the aerial shouldn't look too unsightly since in the summer months the Club Contest occurs during daylight and all passers-by would be able to see the aerial.
There is a set of criteria regarding aerials: they can be a) compact, b) efficient or c) wideband but never all three. Meeting two of the criteria is possible and this was my original hope – an aerial which was compact and wideband.
Here are the various designs which I considered and how they compare to the three criteria. I stress that in this discussion, I am going to simplify some of the considerations for the benefit of the less-experienced amongst us so some of what I say may seem simplistic to the more-experienced operators but I hope they will excuse me in this.
I briefly thought about putting an aerial in the loft space. The advantages of this would be the fact that I wouldn't need to dismantle the aerial for each event and, being hidden from public gaze, it wouldn't matter if the aerial sprouted odd bits of wire for loading, etc.
However, experiences on 6m and 2m using a loft aerial indicated that the traditional roof structure of big oak trusses and thick Yorkshire stone slates had a large detrimental effect on signals. In addition, copper pipes to and from a loft-mounted cold water tank and the presence of a TV aerial in the loft space dissuaded me from this line of thought.
Martin G8JNJ has published some of his experiences with loft-installed aerials which suggested that there was a possible loss of around 5dB due to the close proximity of the building structure. I think that Martin's findings were with a modern roof structure so I anticipated greater losses with my roof structure. Since I was after a compact, wideband aerial, I couldn't expect to have an efficient aerial and the loss of an additional 5dB might prove to be too punitive.
Further consideration of the fact that our roof slope is fairly shallow, and thus the headroom in the loft is restricted, convinced me to disregard loft aerials.
My next thought was for an external aerial – in this case a vertical aerial, or a Marconi. These are usually a quarter-wave long (or high) and to be effective require a good earth connection. The first problem here is that a quarter wave at 3.6MHz is nearly 21m and erecting a 201 high vertical is a bit of a challenge.
I have a couple of 12m Spiderbeam poles plus several 10m fibreglass fishing poles which I use to erect my aerials. Compared to the Spiderbeam poles, the fishing poles are very lightweight and I usually discard the top two sections as they are too thin and whippy. Even after doing that, I still only use the fishing poles for light loads, eg. as end supports for a dipole in conjunction with a Spiderbeam pole as a support for the centre and the feeder. When I use my Spiderbeam mast, I usually guy it at the top of the bottom section and this seems to be adequate for a 10m high mast – as with the fishing poles, I don't normally use the top two sections as they're too bendy despite being well made.
However, if I use a 20m high pole then it does need adequate guying even if it is only erected temporarily and doesn't need to be able to withstand the rigours of winter. The road outside my garden is a bus route and leads to Tesco's supermarket, so it's quite busy and so I dare not risk the pole falling on to the road. “Adequate guying” requires a bit more space than I have available so realistically a 20m vertical is out of the question.
I could bend over the top of the vertical and make an inverted-L – the vertical length plus the horizontal length should equal a quarter-wave length. As I said earlier, the longest horizontal length I can achieve in my garden is 13m, so this would mean that the vertical would need to be 7m high. Bearing in mind that the pole is supporting the end of a 13m section as well as the feeder, then even this is out of the question as the requirements for guying space are still too great!
It is possible to remove a section of the aerial and replace it with a suitably-sized coil – a process know as “loading”. I could add loading to the vertical to reduce the height but this has its draw-backs. If you consider the current distribution on the aerial, at the end of the aerial, the current is nothing – it has to be since there is no where for the current to go to – and so the radiation is a minimum at the end of the aerial. The greatest radiation is where the current is highest – at the feed point – and for the vertical aerial this is at ground level. From a construction viewpoint, it is easiest to add loading to a vertical at ground level where the coil can be suitably supported and any weakness in the aerial's structure can be easily countered. However, adding a loading coil at the feed point where the current is greatest means that the part of the aerial with greatest radiation is affected.
It is possible to add loading coils at other points in the aerial but as the loading point is moved away from the feed point the size of the coil has to increase until at the end of the antenna wire, the size is, theoretically at least, infinite. This means that there is more weight added higher up the mast where you least want it and can make a major problem out of supporting the aerial and loading coil.
An alternative method of loading is linear loading where wires are paralleled to the aerial wire but I felt that this would be difficult to erect and take down and that storing the bundle of wires would be awkward.
I did try out another method of reducing the size of a vertical aerial – that of winding the wire helically along a pole. This method is frequently used to make lower frequency aerials for mobile operation and the design I followed was published in Practical Wireless about six years ago. The end result was an aerial which was about 8 feet high but the bandwidth was extremely narrow. By “narrow”, I mean that the range of frequency where the SWR was less than 3:1 was about 5kHz – just slightly more than the band-width of an SSB signal. In the 80m Club Contest, the range of frequencies is 175kHz which is rather more than the 5kHz bandwidth I measured so I would definitely need to use an ATU. Although this particular design was compact and it may have been efficient, it most certainly was not wideband.
If I used this aerial for the contest, I would have to use an ATU and re-tune after each change in frequency. As the tuning was fairly fiddly, I have shelved this particular project for the time being but may dust it down some time in the future and investigate using it with raised counterpoises and try to broaden the bandwidth with a capacity hat.
For me, the major drawback with most vertical aerials is the requirement for a good ground or earth. The "ground" provides an earth return path for the aerial and acts as a “mirror” for the vertical quarter-wave. It can thus can be considered as creating a mirror-image of the vertical quarter-wave to produce a virtual dipole – albeit a vertical one. There is a lot of talk amongst radio amateurs about what constitutes a “good ground”, how many earth stakes are required, how many buried radials are necessary or how long they should be. Two things are for sure and that is that my garden is not large enough for even a “barely adequate” earth and neither am I prepared to put in the work involved in burying long lengths of wire to form a ground mat.
A ground mat can be created by using chicken wire and allowing it to “sink” into the grass, but I have to remember the fact that the lawn is walked over several times a day and not just by me – if my XYL should trip over a sheet of netting, I would definitely be in bother.
It is possible to use a counterpoise in place of a ground connection and this has the advantage that the entire aerial system can be mounted above ground level. The reason for doing this is to lower the direction of maximum radiation towards the horizon and hence achieve longer distance QSOs.
In my case, I don't need this as I want to achieve short- to mid-distance contacts. I do have a whip with counterpoise for 40m but have not had much success at my home QTH. When I used it mounted at ground level at a temporary location in Hereford, in one session of about 3 hours I made about ten contacts with Algeria, Belarus, Bulgaria, Croatia, Holland, Norway, Russia and Spain but not a single one in the UK. I think this demonstrates that the distribution of radiation from a vertical aerial is suitable for medium to long distance QSOs and not for short to medium QSOs which I wanted for the Club Contest.
So if verticals are not ideal for my situation, what's the alternative?
My next thought was an aerial which doesn't need a ground system and the most obvious form of this is a half-wave dipole. The attraction of a half-wave dipole is obvious – they can be efficient and wideband. However, the dipole cannot be described as compact.
For example, a dipole for the 80m band is 40m long – more than three times the longest space I have available in my garden. However, there are ways to reduce the length of a dipole, the simplest of which is to droop the end of the dipole legs. Because the ends of a dipole are high voltage, they must be kept out of reach of people and animals which limits the amount of drop possible. If I erected the dipole on 10m high poles, the most I could reduce the length of a dipole is 16m making the overall length 24m – nearly twice as long as I can manage. So I need to find some other way of shortening it.
An electromagnetic wave in a vacuum travels at the speed of light – after all, light is an electro-magnetic wave as is a radio wave. That same wave travels a little slower in a piece of wire – not enough to make a difference to the length of an aerial but the difference can be measured – if you're quick! However, in coaxial cable, the difference in speed is significant and it's necessary to reduce the length of critical pieces of coax but what is known as the “velocity factor”.
For example, depending on the dielectric between the centre conductor and the braid, RG-213 has a velocity factor of about 0.66 which means that a half wavelength of coax for 80m is not 40m but about 27.6m. So a short aerial could be made from coaxial cable. However, RG-213 coax is heavy and an aerial made of of RG-213 would need some hefty supports as well as being fairly expensive. RG-58, although lighter than RG-213, isn't a lot better when you're considering an 80m dipole and the reduction in length still isn't enough for my garden.
In the end, and purely as an experiment, I went to my local DIY store and bought a 50m roll of speaker wire. It's fairly thin stuff comprising 13 strands of 0.2mm diameter and insulated with PVC so that wire is about 2mm in diameter. With this, I made a dipole for 80m and then reduced the length by winding the middle part of each leg round a bit of 32mm plastic pipe until each leg was 6.5m long and the overall length was 13m. This was not very scientific and I had to use an ATU to get a reasonable SWR but I managed a couple of contacts. I very much doubt that the aerial was in any way efficient or even resonant in the 80m band. However, it did prove that I would be able to get some HF contacts from my garden and so I decided to try something a bit better.
One way to reduce the length of a dipole is to use loading coils. This is vaguely what I achieved with my simplistic approach although it was more by luck than judgement that I achieved anything remotely like a workable solution. However, there is a more accurate approach to the problem. As I mentioned when considering vertical aerials, the position of a loading coil determines the size of the inductance required. The lowest value of inductance required is when the loading coil is close to the feed-point but this is also where the current and hence radiation is greatest. As the coil doesn't radiate, putting loading coils close to the feed-point means you lose part of the greatest radiation – not very helpful if you want the maximum efficiency from the aerial. If the loading coils are positioned at the ends of the dipole legs, the value of inductance required in each loading coil is very high. This means the coils would be big and heavy. Again, not very helpful.
There is, however, a very useful web-site to assist with the design of what are known as electrically short centre-fed dipoles: http://www.k7mem.com/Electronic_Notebook/antennas/shortant.html.
This site is interactive. Put in the centre frequency, the overall length of the dipole – in my case 13m – and the wire diameter and it will offer you a number of designs. You can select one of these or enter your own design, specifically the position of the loading coil from the feed-point, and it will then calculate the inductance of each loading coil. Another page will allow you to enter the dimensions of the coil and then calculate the number of turns you need to generate the required inductance.
Using this web-site, I designed an electrically-short, centre-fed dipole in which I chose to put the loading coils in the centre of each 6.5m long dipole leg. The calculator page told me that I needed a loading coil of 66.64uH and that I could achieve this using coil formers 32mm in diameter by winding 96 turns. Using the same speaker cable as before, I made the aerial, winding the two loading coils in the middle of the continuous wire, erected it and measured it with the club's MFJ Antenna Analyser. I found the resonant frequency was a bit higher than 3.8 MHz so I took a turn off each coil, thus lengthening the free end, so that the resonant frequency of the overall dipole was just outside the top frequency for the Club Contest.
As I expected, the bandwidth was very narrow and if I tuned away from the design frequency then the SWR rose a lot. I fed the aerial with RG-213 coax which meant that I needed a centre support as well as one at each end but using a balun at the feed-point didn't seem to have any effect. Consequently, I didn't use one simply in order to save weight at the top of the centre support. Although I needed to use an ATU to present a low SWR to the transmitter, I used the aerial for the next couple of years in the 80m Club Contest.
Of course, having to re-tune the ATU after each change of frequency slows down my rate of making contacts but, by creating a table of ATU control settings before the start of the contest, I can achieve what I consider to be a reasonable contact-rate. My limit now seems to be the number of stations who can hear me and not the speed I can re-tune the ATU.
As an aside, I recently bought an MFJ MF225 Antenna Analyser which doubles as a VNA – Vector Network Analyser – and this showed that the aerial was actually resonant at 3.776 MHz – just outside the top of the upper section of spectrum used for the contest – and had a very narrow bandwidth of only 70 kHz between the 3:1 SWR points. Over the range of frequencies used for the Contest, the SWR varied from 1.2 to 4.8 which explains why I need to use an ATU. Whilst the electrically-short dipole is compact, it definitely isn't wideband! Of course, I don't even know the efficiency – all I do know is that outside of the RSGB 80m Club Contest and using 100W I've had “real” signal reports of 59+20 from the Isle of Skye and from Cornwall so I'm obviously getting out with a signal.
During the last couple of years of the 80m Club Contest, I've rarely been able to work local stations which is probably due to how high I erect the aerial. Looking back in my log book to my first attempt at the Contest, I see that I had only five contacts and they were all with stations in either Huddersfield or Ossett - all within 30 miles of my QTH. For the next event in the contest, I mounted the aerial higher and this time made ten contacts all of which were at least 100 miles away – no local contacts at all! For subsequent events, I have mounted the aerial slightly higher still with the centre about 10m high and the ends about 8m high giving a slight inverted-vee. However, the weight of the loading coils tends to mask this appearance and make the centre section look a definite vee whilst making the outer sections more or less level.
I presume that the lack of local contacts in the contest is a result of the aerial height affecting the take-off angle of the radio waves – at a low level, reflections from the ground reinforce the signal and direct the signal more sky-wards so that the skip distance is short and hence contacts are nearby.
Because this aerial fits my garden, is convenient to store and is easy to erect and take down, I will probably continue using the design although I am considering several modifications to, hopefully, improve it.
I am planning to move the loading coils outwards to the end supports and then extend the aerial wire and let it hang down alongside the support pole. To achieve this, I need to increase the size of the loading coil but because the coil is now close to the end support, the weight of the coil will be taken by the support pole. Since the central radiating section will now be longer, and probably more level, I hope to get better performance. I may also reduce the height of the centre support to try to adjust the radiation pattern by using the ground effect so that I can make more local contacts although I risk losing the slightly more distant stations. I also anticipate that making the dipole straighter and more level will introduce some directionality which is not something I've noticed much on the current version although lowering the height may counter this tendency. In addition, I'll use thicker wire and see if that helps to improve the efficiency by reducing the DC resistance of the wire.
It is possible to broaden the band-width of an aerial by using multiple wires spaced from each other – the cage dipole is a excellent example – but because of my desire for easy erection, dismantling and especially easy storage, I have not followed this up as I feel multiple wires would prove tricky to handle.
I had thought about using a loop aerial and there are basically two types of loop – the half- or full-wavelength loop and the small transmitting loop.
A full-wave loop is a big aerial – usually a wave length long – and can be erected horizontally or vertically. If I tried to erect a full-wave loop for 80m horizontally, I'd take up not only all of my own garden but also my neighbours' gardens on both sides. If I tried to erect it vertically so that it doesn't overhang either of the gardens next door, I would need masts about 30m high to ensure that all the current-carrying wire was out of reach of people and animals. So a full-wave loop is out of the question – it might be efficient and broadband but it certainly isn't compact.
However the small transmitting loop does have possibilities. As its name suggests this is a small loop and it differs from loops used for receiving by having no active electronics and by being only a single turn. The significant point is that the circumference of the loop should be about one-tenth of a wavelength or less. Typically, a STL for 80m would be 1m or possibly 1.5m in diameter. Users of these devices claim that when tuned they are very efficient but the drawback is that the STL has a very narrow bandwidth. There are different ways of coupling the transmitter to the loop but most of them involve the use of variable capacitors to re-tune the loop if the operating frequency is changed.
One variation of the small transmitting loop is to use a metal coil – sold under the name of “Slinky” - to form a helical loop and thus possibly make it slightly more wideband. Quite by chance, I recently found an article about the “Slinky” loop in a booklet belonging to John G7ELX which gave some useful information. Although I have seen the proposal several times in the past, I've always regarded them as best suited to working with low power. The small transmitting loop is a high-Q device which means that even using QRP high currents and voltages can be generated in the tuning section and this requires some careful construction. I've not got round to testing the idea but Peter G4NTA made one of these “Slinky” loops and found it to work quite well so I may well give it a go. With winter coming on, this could be a useful project to work on in my shed since the size of a loop for 80m can be around 1m in diameter and so the construction is not going to need a lot of time spent outside in the rain and wind. Whether a small transmitting loop is suitable for working with 100W, which is what I use for the Club Contest, remains to be tested.
A couple of years ago, I found information about a multi-band aerial designed by Mike G7FEK. The final form of this aerial was developed from a simple end-fed Marconi for 80m and uses the opposing harmonic relationships of two ¼ wave elements so that they could be fed on odd harmonics without mutual coupling. It has been described as a “nested Marconi”. The aerial works on 80m, 40m, 30, 17m, 15m and 12m and can be enhanced to also work on 160m, 20m and 10m. The basic form of the aerial is 14.2m long and 7.4m high but by increasing the height by 1/2m, I could reduce the length by 1m and so fit this into my garden.
I started out to make some initial experiments with this design but realised – fortunately before erecting the aerial – that decreasing the length so the two legs are in a straight line which would fit my garden meant that, depending which end is the shorter end, the centre support would either be in the middle of my shed or in the middle of some rose bushes. If I reverted to the original dimensions but put a bend in the line, I could put the centre support on the lawn. I have got as far as erecting this aerial but have not been able to trim the counterpoise to give a 2:1 SWR as recommended in the construction details. I've not yet got round to sorting out this problem so this design is on hold for a while.
That brings me up-to-date with 80m aerial designs to fit my 13m long garden.
Back to 160m
After all this, I'll return to the original question “How do I erect a top band aerial in my garden?”
Because of the proliferation of adverts for commercially-built aerials, the beginner radio amateur could be forgiven for thinking that the only “good” aerials are expensive full-sized dipoles or verticals which require efficient earthing systems. This is far from the truth. Every location is unique as regards aerials and a commercial aerial may work superbly well for one person but not for another. Spending a lot of money buying a commercial aerial to cover top band – assuming you can buy one – doesn't teach you anything and may well not work. Building your own aerials need not be expensive and the learning experience is well worth the effort. Of course, it helps if you keep notes of what you did and how successful – or not – a particular design is.
My own experience has shown that compact aerials are not wideband. We know that the converse is also true – that wideband aerials are not compact. So one answer to the question would be to consider instead some other, possibly less well-known, solutions.
Before doing that, we should ask what type of QSOs are wanted. If long-distance QSOs are the aim then a vertical aerial which produces its greatest radiation with a low angle take-off or a horizontal aerial mounted as high as possible would seem appropriate. On the other hand, if fairly local QSOs are wanted, then a lower-mounted horizontal might be better.
I have to say at this point that there are what appear to be dubious designs which are trumpeted on the Internet, mainly by their inventors, including some designs which do not seem to conform to the accepted laws of physics. Such designs lead to a lot of heated exchanges which make amusing reading but don't add a lot to the sum of human knowledge.
Some such designs which spring to mind are the E-H Antenna which is only a few feet long for a top band aerial, the Crossed Field Antenna, the Tapered Area Small Helix antenna, the Controlled Current Dipole and the “Tak-tenna”. Of course, the only way to prove whether a radical design works is to apply common sense and even to actually build it and try it out.
For example, the “Tak-tenna” is essentially a short dipole about 2 ½ feet long with capacitative loading at the ends by means of a large spiral of wire. According to some, it works superbly – according to others it only works to a small degree. Critics claim that the feeder is an essential part of the design as it radiates more than the aerial itself. I cannot see how the "Tak-tenna" – a very short dipole with large capacity hats at each end – will work any better than what I have already. There may well be much better alternatives.
Of the more accepted designs, one solution is the tuned doublet – that is, a dipole which is as long as you can make it with twin feeder to a balanced ATU. Recent suggestions for the tuned doublet is to size it so that half the top length plus the length of twin feeder is a quarter wave length at the lowest frequency, connect the twin feeder to a 4:1 balun and then use coax to connect to the ATU. However, assuming that a reasonable height for the feed-point is 10m, this would mean that for a top band aerial, the top length is 20m and even this may be too large for most urban gardens – it certainly is too big for my garden. I have made a 30m long version with 8m of twin feeder which I have used with success for Churches On The Air on 40m and 17m. Of course, since it's not resonant on any specific band it needs to be used with an ATU and I haven't been able to test it on 80m or even top band.
Another standard design is the inverted-L which is a quarter-wavelength mounted vertically but bent horizontally part way up. Depending how much of the aerial is horizontal, the efficiency is compromised – the horizontal section acts as a capacity hat and does very little radiating. However, a capacity hat also lowers the resonant frequency of the aerial so if your vertical aerial is resonant a little higher than the frequency you want, adding a capacity hat – which could be as simple as a piece of horizontal wire or even the supporting guys – could put things right. I'm not going to discuss capacity hats in detail since, for me, they would prove awkward and so I've not used them much.
If you are prepared to forgo an S-point or two on your signals there are some interesting ideas for compact aerials in various publications. The books published by the G-QRP club especially have some intriguing designs. For example, there is an idea for a non-inductively loaded dipole for 40m which is only ten feet long with suggestions for re-sizing it for the 80m band so that it is the same length. Althpugh I have built a version for the 80m band I have not yet given it a proper test.
There is also an idea for what is basically a triple version of my electrically-short dipole which increases the impedance – and hence the efficiency – and slightly increases the bandwidth. It uses a fair bit of wire as it requires six loading coils but it may well be worth testing. If we have a cold or wet winter and if I can get a good supply of wire and if I feel like spending time in my shed winding coils, I'll consider making one and giving it a trial. However, I can foresee problems with this design in erecting it and in storing so much wire and so many coils.
Past issues of Practical Wireless can also bring to light some interesting aerial designs. Recently, I was reading an issue from 1995 and found a helical vertical for 80m intended for use on a boat. The total height was about 18ft which is reasonable but it relied on the boat hull for a ground plane. I could substitute a counterpoise for the ground plane which could make the design viable in my garden so this is another one to keep in the “Pending” tray.
Another source of ideas for aerials is the book “Antenna Topics” by Pat Hawker G3VA. It's been out of print for some time but if you see a copy at a rally, it's worth getting hold of it. The information about any particular design can be a bit sparse but experimentation is part of the fun of aerial building. And you may find the ideal design for your particular situation!
The G7FEK “nested Marconi” which I mentioned earlier looks to be a viable alternative and modifications suggested on the web-site include adding a loading coil to cover the 160m band. As I said, I haven't yet been able to correctly adjust the counterpoise but if I do get round to “tuning” my 80m version in the next few months, I'll report on my experiences using it. With a successful implementation for 80m, I'll then look at the modifications necessary to cover 160m.
Another alternative seems to be the small transmitting loop although, because of the need to re-tune it with every change of frequency, this would seem to be most suitable when operating on a fixed frequency or using modes such as PSK31, JT65 or WSPR which either use narrow bandwidths (and so there is little need to change frequency and so re-tune the loop) or which don't require high power. The good feature about this design is its physically small size. There are claims for high efficiency from the small transmitting loop but none for its wide bandwidth.
The book "HF Antennas for Everyone" published by the RSGB contains a design by G3RFG for a six-band portable aerial which is a centre-loaded vertical. The design uses two different centre coil - one of which is tapped - and a variable length top section to accommodate all the frequencies. The overall height for top band is 5.3m and it is guyed just below the centre loading coil. The radials are 1.2m long and fasten to the sem guy oegas as the supporting guys. I've been looking at this design for some time and feel that it is ideally suited to my garden. I shall eventually get around to building it and seeing if it is suitable for the 80m Club Contest. Even if the radiation pattern proves unsuitable for the contest, I think it will still prove useful as an easily and quickly erectable semi-portable aerial for days out in the country. Its design and construction suggests that it could prove useful for a semi-permanent aerial in a small garden.
To end with some suggestions for a top band aerial for a small garden, I offer the G7FEK nested-Marconi, the electrically-short centre-fed dipole or the full-sized G3FRG vertical
Although none of the designs mentioned here may be the best aerial possible, any one of them could be the best aerial possible your a particular situation. Remember that the old adage still applies: any aerial is better than no aerial at all. The only way to find out whether an aerial will work in your location, is to try it.
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