Possibly a silly question but what type of wire should I use for a buried radial field?
So far I’ve had the following suggestions from several people of varying wisdom!!!
Use antenna wire which can be bought from radio shops (usually copper with a plastic outer)…quite an expensive option, but should work well.
Use 12 gauge bare copper wire…probably the best performing (I believe that this is what they use when they build commercial radio towers) but I think this will be hideously expensive (probably prohibitively so).
Use fairly thick automotive/marine cable…probably the most likely candidate in my mind.
Use the old reel of CAT 6 cable that I have laying around!!!..I’m really not convinced with this idea! This was suggested because it is extremely cheap and I already have a couple of hundred meters of the stuff laying around from a previous computer installation project which is probably never going to be used (and thus probably eventually destined for the dustbin). I currently use this for the radials of my portable setup with some success but I’m not sure how well it would handle being buried for several years!
Use electric fence wire (either galvanised steel or aluminium)…this is by far the cheapest option but I’m not sure how well it will handle being buried under ground. I guess that it’s tough and the aluminium would probably be ok? I suspect that steel wire would just rust. Theoretically I guess they galvanise steel to prevent it from rusting, but I’m still not convinced that it will last very long!
What’s everyone else’s opinion? What have other people used when they’ve buried radials?
Obviously this project means digging up most of my back my garden, so I want to make damn sure that I only have to do it once!!!
The best wire would not corrode, or would do so slowly. It would not need to be thick as the total current in the radials is the same as that in the main radiator so the current in each wire is the total current divided by the number of radials. But on the other hand, the role of the radial field is to create capacitive contact with the conductive ground (if you have any of that rare stuff) so that the ground currents are spread over a wide area and the effect is of a conductive and continuous sheet. A ground plane.
I like the idea of aluminium wire if you can find some. There are indications from the modellers among us that the benefit of doubling the number of radials is marginal beyond a certain level, when elevated radials are modelled. How similar the buried radial situation is, I don’t know. But it seems intuitively correct that once the ground impedance is reduced to say 1 ohm, reducing it to half an ohm will only make a minor difference to the efficiency, when considering the R(radiation resistance) + R(ground losses) as the total impedance. I suspect getting it down to 5 ohms would be quite an achievement.
EG. If you construct a quarter wave vertical which would have a nominal impedance of 32 ohms, and its SWR is 1.0, that suggests there is 18 ohms of loss resistance and the efficiency is something like 32/50. Not many backyard 80m verticals would be that good.
I agree that steel wire is probably not ideal. Won’t last long in the ground (steel garden stakes are severely corroded after 5 years). Galvanising delays the process, but it’s still going to dissolve eventually. Though the rust probably increases the conductivity of your soil?
A good solution could also be field cable, which is used in the army for the telephone connection. This cable is very robust and often inexpensive to buy. I bought a 800m roll for 20 Euros at a flea market and built many antennas with them.
The couples are hard to separate, so I would bury it as it is. The insulation is very solid and I would close it at the buried ends so that no water penetrates.
If the available area is very small, e.g. on a balcony, chicken wire is often placed under a carpet.
73 Armin
Aluminium fence wire is cheapest and best. 400 m / 1.6 mm are 24 quid on Amazon.
Don’t bury the radials too deep, best would be the wires lie on the ground. So let them just disappear under the lawn.
It would help knowing the number of radials you are planning to bury. It won’t be the same solution for 8 buried radials or for 100 to 120 radials, which is what some “experts” recommend for an optimum performance.
Personally, I wouldn’t go for such a huge number of radials and I would do it with not more than 16 (max). My choice would be a cheap and thin copper wire with plastic insulation like that old reel of CAT 6 cable that you have laying around and never deeply dug into the ground, just slightly covered with the first few centimeters of the ground together with the lawn layer. That will last a number of years for sure and assuming you want to keep using that same antenna in let’s say 15 years, you’ll be able to easily replace the wires in case you feel like you are needing to.
Over engineering is something I always try to avoid. Some of the pyramids in Egipt like those in the Gyza valley have lasted several thousands of years, in spite of some vandalism they suffered over the years, but I honestly don’t think our antenna systems need to be engineered for such long time.
Good luck with your setup and keep us, please, informed us of your final solution and the outcome.
73,
Guru
P.D. if you could install elevated radials sloping down at an angle rather than buried, your vertical would perform better and you would spare all that digging work and worries about corrosion and durability of the wires underground. Cheers!
From what I have read, the optimum is around 16-20 quarter wave radials. More than about 20-30 radials & I’m led to believe that you are into diminishing returns. The marginal improvement isn’t worth the effort apparently.
As I’m planning two separate systems for two separate sites, lets take them one at a time.
First site is the field (around 3 acres):-
I should have no problem doing 30 radials @ 10 meters long, which should be perfectly adequate to run both 40m & 20m.
I’m debating the idea of putting down longer radials for 160m or 80m. I’ve got no way of getting a 1/4 wave vertical for 80m or 160m, but I could certainly use an inverted L. Not sure if it’s worth the extra effort & expense though.
Second location is my back garden:-
I’ve yet to decide how many to put down here. I’ve not got enough space for a 1/4 wavelength but…
There’s some research that was done by a guy called Rudy Severns (N6LF) which is well worth a read. Basically his research shows that it’s more about the overall length of wire in the ground than the actual number of radials.
That is to say that 10 x ten meter radials will have (near enough) the same effect as 20 x five meter radials.
As I only have 5 meters of ground space to play with in my garden, so based on the theory above, I’m going to have to compensate with more radials if I want to get decent results.
I’ve heard that (as a very rough guide) you should have 4 times the wavelength of the lowest frequency. So on 40m this would equal 32 x 5 meter radials. If I want to go to 80m then this doubles (gulp)!!!
To answer your original question (how many radials I intend to lay), I guess that I should aim for around 30-40 radials which should give good results on both 20m & 40m. It should still be usable on 80m but I will have to accept a slight loss (I don’t think that burying 60-70 radials for 80m is a sensible proposition)!
Unfortunately I don’t think that this is an option:-
My back garden has too many pets (& people) to get tangled in the wires if I try elevating the radials.
The field on the other hand needs to be a little discrete, so I would prefer to bury them out of sight. The plan for the field is to bury the radials & just lob up the vertical when I want to use it. That way nothing is visible when I’m not there (apart from the ground rod sticking a few inches above the ground, which wouldn’t be noticeable from the road).
Hi James,
Regarding your field location, the decision on whether the effort & expense worths, depends on how fan you are of the low bands and how much you want and really can use them. A short coiled vertical will always have limited results in performance compared to a full sized one, but it can surely give you some level of satisfaction. I remember being 1st place Spain of the 2009 ARRL 160-meter contest as single op., low power with a half wave bazooka dipole for the 80m band and the help of an antenna tuner. Digging 30 radials or even 16 only of the necessary length for 160m band (even for 80m) is not a trivial amount of work…
Regarding your second location, OK that the option of elevated radials is not on the table. I understand perfectly your reasons for that. I this case, I would do, as you suggest, the higher number of radials you feel like willing to dig in the ground with the maximum possible length.
Did you find acceptable my advice about using that old reel of CAT 6 cable that you have laying around?
I would really like to do more on 80m, particularly chasing SOTA contacts. I’ve used it a few times but my previous antennas really haven’t been up to it (inadequate ground system, or too short).
I’ve always wanted to have a play on 160m but would say I’m not overly bothered. I see it as a nice to have.
20m, 40m & 80m are the bands that I’m interested in. I’m swaying towards the idea of laying an “over engineered” radial system for 40m. This will obviously be totally over the top for 20m (but who cares), and usable on 80m (accepting a slight reduction in efficiency) with a view to using an inverted L on 80m.
160m would be nice to play with but (as you said), “it’s not a trivial amount of work”.
I need to have a look and see how much I’ve got left on the reel. I’ve probably got enough for the small system at home, but probably not enough for the large setup in the field.
A couple of people have commented on the idea of the aluminium electric fence wire.
My initial thoughts are to use the CAT 6 cable at home and go for the aluminium fence wire for the big system at the field.
Some people lay chicken wire/fence netting/whatever the proper name is just on the ground and let the grass grow through it. Supposedly it works well for verticals as it provides a large and effective ground plane effect. Might be worth a try? Aldi sometimes has covered chicken wire on sale
I used a Cushcraft R7 for a decade with excellent results. I had copper clad steel wire for radials…eight of them. But the ground in each of two locations was highly conductive. What is your ground like? Eight would be a minimum, sixteen if you have lossier earth. You only need to cut, not dig them in. A square spade that goes down an inch, is pushed forward, and opens the sod is all that’s needed. Best to do so after a rain.
Dont use aluminium, it will corrode rapidly and disappear into white oxide. In the same way you should not leave an aluminium antenna on the ground or in grass for a long period.
Bare or covered copper, whatever is most economical. CAT5 or field telephone wire (normally a mix of copper and stainless steel strands) can be cheap as Armin suggests. Or surplus equipment wire if you can get it.
In terms of how many and how long, that is covered in detail by ON4UN in his books and also google N6LF optimum radials.
I have been through this on my home station over the years, I have a pair of 80m phased verticals with 3.4Km of radials between them and a 160m L with 3Km of radials. All copper of various descriptions, still in good condition after 14 to 16 years.
73 Gavin
GM0GAV