Other SOTA sites: SOTAwatch | SOTA Home | Database | Summits | Video | Photos | Shop | Mapping | FAQs | Facebook | Contact SOTA

Is using a metal shed as a counterpoise a stupid idea?

I’m looking at having a slight reshuffle of antennas to see if I can get something a bit more effective on the lower bands (40m & 80m).

I wondered about running an end-fed wire from the shed at the bottom of the garden up to the roof of the house.

I’ve heard with wire arrangements like this that it’s better to have the feed point as far away from the house as possible, so I was going to put a remote tuner (such as an SG-230) inside the shed and run a fairly heavy duty/low loss feeder cable to the shed.

Whilst considering my options with regards to counterpoises, it occurred to me that I already have a big lump of metal (ie the shed itself) right at the feed point!!!

I figured that people use their cars as a counterpoise for mobile operations, albeit that mobile setups are generally very inefficient (probably more due to the short loaded whip). Could I use this metal shed as a counterpoise:-

So I guess I really have 2 questions:-

  1. From a safety point of view…would someone be likely to get an RF burn if they touched the shed whilst I was transmitting (I’ve not heard of this being a problem with mobile setup’s in cars, so it may not be a issue). I would be running a maximum of 100 watts (which admittedly is still plenty to give someone a nasty RF burn).

  2. How effective do we think it would be?

I’m interested to know what the antenna experts out there think. Will this work or is it a really bloody stupid idea?

Hi OM ,
Well, it should work. Give it a try. I have a metal shed 18 X 10 feet in
my back yard and I have 3 mobile antennas fixed to the roof and they work pretty well, at least as well as a mobile in the car. My shed isn’t in a very good location, there is a big tree with limbs hanging over the roof near the antennas and they still seem to work OK. I’ve worked a few SOTAs from there and quite a few DX contacts, etc. with just 50 watts or so.
73 let us know how it works!
John, K6YK

Hi James,
In answer to the question, when you need radials or a counterpoise the bigger the better and in as many directions as possible. Would the metal shed work as a counterpoise - yes, would it be a good one - probably not - but if you have no other choice …

But I think you have another choice. If you are able and willing to run a wire from the chimney pot down to the end of the garden - and there’s enough length to get an 80m end-fed half-wave in, then there’s also enough length to get an off-centre-fed 80m dipole in. That antenna needs no counterpoise. OK, the coax feed will come down about a third of the way along its length and that might be a little unsightly but perhaps the 1/3 along is near enough to the edge of the house that you can bring it down the wall there and so it would only have a short length of coaxial cable visible. The end of the coax at ground or first-floor level can then go into your remote ATU (presuming you already have one - otherwise you don’t to buy one for this antenna) and then from there into the shack. An off-centre fed 80m dipole will work well on 80 and 40 as well as 20,15 10m and “OK” on the WARC bands with an ATU (or rather an automatic matching unit).

You can build or buy. It’s good to build the antenna yourself but if you prefer to buy - this one is good: https://www.aerial-51.com/model-807-xx/
A compromise may to buy a 4:1 Balun but then build the rest of the antenna yourself - it’s only wire after all.

73 Ed DD5LP.

James, I forgot to mention that having the shed grounded would
take away the RF burn concern.
73,
John, K6YK

That small shed is such a small percentage of a wavelength at 40 and especially 80m, it won’t do much. You’re better off having the feedpoint at ground level with some 1/4 wave radials extending along the ground.

It is difficult to give a full answer without having some dimensions to play with, but I have several thoughts which may or may not apply, and a suggestion.

First of all you mention putting the ATU in the shed. I don’t think this is a good idea as the antenna wire will begin its journey inside the shed, enclosing what may be the high current part of the antenna completely in metal. Even if you arrange things so that the run from inside to outside the shed is very short you will have an expanse of metal doing strange things to the radiation pattern. Also as said above it is going to be a poor counterpoise, although you could improve it a little by bonding a wire to it and running it along the ground, but even so your shed looks to be at the far end of the property so you can only run a counterpoise in one direction. Eds suggestion of an OCF dipole is a good one but I suspect that even with running the antenna from the chimney your plot is unlikely to be big enough to accommodate 40 metres of wire. So I think that your idea would lead to an antenna that would work, just not very well.

One possibility is to have a trapped dipole, the traps are a little inefficient but they would shorten the antenna by a useful amount. Another idea (which I have tried and know it works) is to have a doublet fed with 300 or 450 ohm ladder line. You could terminate the ladder line at an outside balun and run a short length of coax into the shack, or if you have a convenient ventilator or airbrick you could run the ladder line into the shack, you would need a tuner with a balun, something like the MFJ-949E works brilliantly - plus this arrangement will give you access to 60m and will even get you some contacts on 160m. Mine does!

Of course, ham radio is a journey, you could have fun trying out all the suggestions!

An end-fed half wave on 80m is also 40m Brian - hence my presumption that a dipole would also fit. Are we talking about an end-fed quarter wave on 80m not an EFHW James?

I thought it was the big shed ! OOPS !

Oh yes, I understand, but gardens long enough for a full half-wave at 80m are not common (mine is but most around here aren’t) and I thought it likely that he was thinking of a shorter length, perhaps a random length, brought to resonance with the remote tuner.

Thanks for the replies so far folks.

I think we are looking at a 1/4 wave Ed.

A bit of measuring, trigonometry and slight guess work (as I don’t know exactly how high the chimney is, although I was able to make a rough guess based on measuring the height of the eves of the house, then add the height of the attic etc etc) leads me to believe that from the bottom of the garden to the chimney is approximately 19.5 meters. This is based on the radiating element starting on a small mast at 2 meters above the ground…just above the height of the shed.

I had also contemplated putting the tuner (which is apparently weatherproof & rated to be left outside) on the outside of the shed…which would probably be a better idea based on Brian’s comments about having the tuner inside the shed.

If I went all the way over the top of the house and secured the wire to the fence at the bottom of the drive I reckon I can get around 38 meters of wire.

Putting a slight dog leg in and factoring in a slight reduction in length due to the velocity factor of the wire, I might be able to get a half wave in for 80m but I was shying away from this idea because there are over head phone/internet cables from the wooden pole in the street. Although not high voltage power lines, there is a significant amount of electrical noise in the area & running antenna wire down between/parallel to these wire seems like a recipe for disaster…both for picking up additional noise & causing interference when I transmit.

Exactly what I had in mind.

As I said in response to Ed, I reckon from the shed to the chimney I can get just under 20m. Factoring in velocity factor for the wire, I reckon I might just get a 1/4 wave for 80m & a 1/2 for 40m.

With this in mind I was going to aim for as close as I could possibly get to a resonant 1/4 wave on 80m & then tune the thing with a remote tuner.

So it’s not strictly speaking a random wire, but might be just a little short to be resonant on 80m.

The problem is the counterpoise. Probably not going to get a 1/4 wave in there because the garden is too short…unless I loop it round the garden (but I think that counterpoises are supposed to be straight)? Hence wondering whether using the mass of metal in the shed as a counterpoise was a viable option.

The consensus on here seems to be that due to it’s relatively small size it probably won’t work very well.

My bad, I should have given the dimensions of the shed.

1.5 meters wide
2.6 meters long
2 meters high

I did wonder that, but wasn’t sure

I was reading these for my indoor second floor antenna grounding.

https://www.w8ji.com/counterpoise_systems.htm

Book by N0AX Grounding and Bonding for the Radio Amateur is a good general reference in North America. I have 12" x 24" thin Aluminum plate under FT817ND now as shown by N0AX in Virtual Ham Expo talk. RF ground is 50 ft of 12 Gauge antenna wire (lowest frequency band 60 m) in addition to safety ground through mains plug. This is minimum I guess and you can add more wires. Like any antenna wire it does not need to be straight but sharp bends may not good idea.

If you connect to the shed with a wire it might be more like capacitance loaded vertical up side down depending on the length of the wire and operation frequency.

73, Jaakko ac1bb/oh7bf

OK, then you will definitely need that ATU on the end of the wire in that case as the impedance will need to be matched - alternatively an UNUN at the end of the wire would also help.

I like the idea of an inverted-V full sized OCF dipole over the house from front garden to rear - the problem with that is that you will get all the noise emitting devices in your house under the antenna - but at least it’s your house and you might be able to address and resolve any interference.

If those phone lines are carrying VDSL2 you will have problems no matter what antenna you put up. Do you already have an antenna up and are you getting interference already? If you currently are getting no interference, the Internet over the phone lines might only be ADSL2 which doesn’t tend to cause issues. Neither to you, nor from you.

As the buildings around you are likely to affect the radiation pattern and at least on 80m you are most likely going to be relying upon NVIS propagation when the CF is high enough, putting bends in the antenna is not going to be critical. Do what you need to do to get the length you need in.

You could also run from the chimney to the two bottom corners of the garden, despite them being so close together. It will work. It won’t be perfect but the more wire you can get in the air, the more wire surface area there is to receive and radiate signals.

To your other comment:

Not as far as I know - as long as a counterpoise wire doesn’t go back over itself (hence effectively shortening its electrical length) - all is OK.

You are not using a tuned counterpoise when you consider using the shed however - it’s more of a “false earth” that you are tuning against.

It is perhaps better to consider this antenna as a “random-wire” rather than as resonant one. My experience with end-fed half wave antennas is that they work best with a tuned counterpoise - which I have been able to make work as 1/8th. wavelength long however 1/4 wavelength is more normal. This of course makes the antenna a single band antenna and any attempt to tune it to other bands with the ATU will be a compromise solution. Hence back to an OCFD as (in my opinion) a better solution - if you can find some way of fitting it in.

73 Ed.

Have you considered a G7FEK multiband antenna? It’s about 15 or so meters across the top, and you don’t need a tuner for many of the bands

Yes, interference is a big problem here. I’m working on that.

I’ve been experimenting with a Log (Loop On Ground) antenna for receive, which seems to give a better s/n ratio. Obviously I cannot transmit into that antenna.

I’ve also dabbled with a “Terminated Inverted U Antenna”, which also seems to be quieter than the vertical that I used to have.

The problem with the Terminated Inverted U is that it is very in-efficient on transmit, though it does transmit with less than 1.5:1 SWR from 160m all the way up to 6m. It’s not spectacular, though it does get out & could be improved by extending the masts to get it higher in the air, but I think that I could do a lot better with a 1/4 wave or a 1/2 wave.

I also want to try a receive only loop. I’ve heard of people living in very noisy locations having great success with a Wellbrook Loop or DX Engineering loop fairly low to the ground at the end of the garden (as far as possible from electrical noise from the house) as their receive antenna, then using a separate transmit antenna.

I also had some success with using two antennas with an MFJ noise cancelling unit to phase out the noise. This can work quite well but it is a bit of a faff that I don’t really want to have to mess around with.

I am tempted by that idea, especially if I decide to use a separate receive antenna, though I do worry about having a transmitting wire so close to internet cables. I don’t want to be the very unpopular radio nut that wipes out everyone else’s internet!!!

I had thought about pulling down the VHF/UHF collinear that I have on the chimney & use the existing mast & coax feed to run a dipole (I already have an unused trapped dipole for 80/40 in the shed). Though I like the idea of the end fed as it could be tuned on most bands, whereas the dipole is slightly limiting.

Curious with this idea. Will 1/8th wave counterpoise work as an 1/8th for 80m is about 10m. The back garden is around 15m long, so a 10m counterpoise for 80m along the fence line is easily possibly (& presumably would also work as a 1/4 wave counterpoise for 40m)?

I did consider it a few years ago (the last time I had an antenna re-shuffle). If I’m honest I completely forgot all about that. I will have another look into that.

Hi James,
My tests with tuned counterpoises were only in open areas (fields or summits) not in built-up areas and my experience although you might think multiples of length might work for different bands - my experience was different length counterpoises were needed for each antenna - and each antenna was cut (both driven element and counterpoise) for a specific band.

If you intend to use a random wire length for the driven element, then you can’t have a “tuned counterpoise” for it. Think of an End-Fed antenna as a dipole with one leg of the dipole laid on the ground and you’ll see that with a short counterpoise, you effectively have to change the length of the driven element to get what is then something like an off-centre-fed dipole - or that’s the way I tend to think of it.

So if using a random length wire the other side will not be a tuned counterpoise - rather just a virtual earth to tune against. I think with a random length end-fed, you might be better with multiple radial wires of different lengths rather than a single counterpoise wire.

Different kinds of antenna have different capabilities as regards the level of interference they receive. My experience is that, in general verticals are normally the worst (and I would include random length end-feds and EFHWs in this category). Then dipoles are better and better still are full wavelength loops and directional antennas such as beams and magnetic loops. Beams and magnetic loops tend to be single band antennas though.

73 Ed.

1 Like

The only stupid ideas are the ones you don’t try.

I would use the shed roof as the ground plane for a vertical antenna, possibly a trapped vertical. If reception on the vertical is noisy, I’d use a separate receiving antenna, plenty of published options, from amplified whips and short dipoles to loops. The vertical will be the best transmitting antenna you could possibly have in a small backyard. My best dx has been obtained using that kind of antenna. Low dipoles are nowhere near as good, in my opinion and experience, that is, ymmv.

73 Andrew VK1DA/VK2UH

1 Like

I can’t find the article right now… but there was a report from an amateur who used a picnic blanket for his qrp /p activities. The underside was aluminium coated. He grounded it with a tent nail.
Full success: he had a warm butt and a good counterpoise.

73 Armin

1 Like

I like the idea of keeping warm in the field.

You don’t need a resonant length if you have a good ATU. Ive used 42 ft and 84 ft of wire with half that length as a counterpoise on the ground for SOTA contacts to 2,700 km from forests in 2019.

However, I have an MFJ remote tuner screwed to the corrugated iron roof of the shack, It is connected to a 25 to 30 m length of wire (not actually measured) that goes up from the far end of the roof where the ATU is located to 10 m above ground and then down again in a sharpish V and then across the back wall of a brick garage.

I supplemented the roof “earth” with three heavy wires running to two earth stakes 3 m apart. There are two bent radials that run along the fence line in opposite directions, one continues across the back fence line. Its a bit short of 30 m. A 1 m length of wire bonds the second ground stake to a copper cold water pipe that crosses the property and runs all the way to the front fence. It tunes all HF bands except 30 m. I have worked 800 km on 160 m with it and on 80, 40, 20, it is about 1 S unit down on my higher OWL fed 5 MHz doublet. For a junky antenna it’s quite good and adequate for most SOTA chases…

So don’t worry about the length of the radiator. Make it long enough to go from the shed to the chimney pot. Put the ATU on the roof with additional weatherproofing where advisable. I understand it rains a lot over there.

Add as many earth stakes 3 m apart as you can to improve on the shed ground point. Add some quarter wave ground wires along the fences and wherever you can fit them… At least 1 per band. They can be laid across the grass and held in place with wire saddles. Don’t put the mower too low when using it and they will be essentially invisible. Use earthing building wire.

Of course it’s a compromise but better 1 s unit down than not on at all.

Install then start working the dx.

73
Ron
VK3AFW

1 Like