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cat 6 cable for radials on a vertical? Is it a daft idea?


#1

Just wondered if anybody else had tried this?

Up until now I have done all of my activations on VHF, but with the VHF bands seemingly getting quieter & quieter (and harder to get the required 4 contacts) I decided to resurrect an old Icom 703 to do some HF activations.

I purchased a telescopic vertical pole (which many SOTA operators seem to use) some years ago which came with a single radial/counterpoise. Frankly it was rubbish and I kind of gave up on it.

Needing a cheap & portable antenna, I decided to pull it out of the spare room and see if I could turn it into something usable for SOTA activations.

I came to the conclusion that it wasn’t performing because it needed a better ground (ie more radials) and it occurred to me that cat 6 computer cable is basically 8 separate wires for each length of cable.

I took two lengths of cat 6 and twisted the wires together at one end (leaving them open at the other end). This effectively gives me 16 radials in total laid out in opposite directions (8 in each direction).

I tried this configuration on my last activation of Walbury Hill (G/SE-001) a couple of weeks ago and managed a fairly rapid succession of 14 contacts in around 15-20 minutes (including 2 USA & 1 Canada). I was running full power from an Icom 703 (which is 10 watts).

At first glance, this appears to work very well for a portable full size 20m vertical.

I’m not sure what the power rating is on cat 6. I would suggest that you wouldn’t want to put any real serious power down it. I have run 100 watts SSB & around 50 watts FT8 through it from my home QTH with 4 lengths of cat 6 cables (effectively giving me 32 radials) with no ill effects. I don’t currently own a linear amp so haven’t tested it with anymore power than this. Frankly, I’m not sure I would dare put any more power than that through it, even if I could!!!

At first glance this does seem to work very well but put aside my personal experience, I wanted to get some feedback from people with a better understanding of antenna theory than me.

Any geeky antenna gurus want to chip in with your theories, opinions or science to back up (or discredit) my theory?

Anyone else tried this (or anything similar)?


#2

Hi James,
That’s an interesting suggestion - although as all 8 wires are twisted together as 4 pairs within the computer cable, I suspect it looks more like one thick radial rather than 8 separate ones. But I’m no expert, so I could be wrong.

How long were these “CAT-6 radials”? Were they 1/4 wavlength long on 20m or just random lengths?

If you want to take a look at an antenna that you can use with that same telescopic fibreglass pole and not need any radials, take a look at a J-Pole antenna (yes they exist on HF as well as VHF) - you may be surprised how well they perform.

73 Ed DD5LP.


#3

Hi Ed,

Thanks for the input.

The radials were cut to a 1/4 wavelength on 20 meters (which if we do the maths, is actually marginally over 5 meters).

I did wonder if the way that the cables were twisted together would cause any interesting or adverse effects. I haven’t noticed anything untoward, but I really don’t know for certain. Hence why I posted the question for collective discussion in the hope that someone who is smarter than me would have an answer.

All I have to go on is my personal experience of actually using the thing. At first glance it seemed to work much better than I had expected.


#4

If the 16 wires were laid out as 2 X 8 wires together at the outer end you would have two ground radials. If the 2 X 8 wires were spread out through 360 degrees you would have 16 radials for the vertical to work against making it much more efficient as a low angle radiator.

I wouldn’t worry about power levels and thickness of wire if I were you, but keep an eye on SWR creepage. If you melt the wire it will cost you pence, if you melt your PA devices it will cost you ££££s.

73 Phil


#5

Thanks Phil,

Just so that I understand this correctly, what you are saying is that Ed’s theory is correct?

In other words the 8 wires in one length of cat 6 would all act as one radial because they are twisted together.

So effectively I have two radials (as I have two cat 6 cables with the 8 cores twisted together at one end)?


#6

I believe that you may have the same result by using single wire instead of CAT6 cable.


#7

Yes GQC and Yes WPJ I agree and am of the same mind. Two radials if the cable is split into two and fed out from the feedpoint at 180 degrees to each other. Should still radiate an effective low angle signal in my opinion.

73 Phil


#8

Exactly.

73,
Walt (G3NYY)


#9

Thanks for the input folks.

I knew that there had to be a flaw in the plan somewhere, otherwise somebody would have already thought of it and it would be all over the internet by now (basically everyone would be using cat 6 for radials if it was that simple).

Having said that, it still makes a very cheap (essentially free) set of radials as my partner is a computer engineer and we have a couple of hundred meters of the damn stuff left over from a previous project. I might as well get some use out of it!!!


#10

Cat 6 or cat 5 cables consisting of 4 pairs of twisted wires are still just conductive wires. Pull one of them completely apart and you’ll have 4 pairs of wires, you can use each twisted pair joined together and it will act as a single radial, 4 of them gives you all the radials you need (if they are elevated off the ground). I use 3 radials, elevated and insulated off ground. A quarter wave vertical with a 3 or 4 radial elevated ground system is a great dx antenna.

The current in each wire is 1/4 of the current that is flowing in the vertical element. For 10 watts the current flowing is calculated using ohms law. I = Sqrt (10/50) = sqrt (0.2) = just over 400 milliamps, so the current in each radial is 100 milliamps. One strand of cat 6 cable will probably carry several amps, perhaps up to 10amps without blushing.

I use mains figure 8 cable or speaker wire split down the middle as the source of strong flexible and light antenna wire. But if you want to use more expensive “antenna wire” that works too of course!

Physical issues…

As computer cables are designed to be terminated to Insulation Displacement connectors which cut through the insulation and scrape an indentation in the wire, they are usually single conductors. And they are intended to be installed and then left alone. So they are not designed for ruggedness and applications where flexibility and repeated bending are requried.

Any SOTA antenna gets unwound, setup, then torn down, then rewound onto a reel or winder many times, so flexible multicore wire is a better bet than single core solid copper. I suggest you evaluate the wire for those physical characteristics when considering wire for antennas.

I agree with you re the single radial vertical. It may well produce a low swr, but then, I have a 50 ohm resistor that is perfect, but have not had many contacts on it… (cue stories of contacts via dummy loads… yeah ok)

:slight_smile:

Andrew VK1DA/VK2UH


#11

Hi Andrew and all,

Yes the run of CAT6 looks just like a thicker wire and the parallel combination would be OK at 10 kW. Due to the plastic insulation it looks electrically to be longer than the physical length, maybe + 20 %. But laying it on the ground will change the resonance in an unpredictable way - wet, dry, gravelly, rocky, snow covered?

A simple ATU will compensate for such variations.

Why use CAT6, CAT 5 will be just as good and no-body wants it these days - cheap?

To overcome the lack of fatigue resistance that may exist with CAT5/6 you could twist on and solder a flexible wire to the end of the CAT5/6 and then use heat shrink cable to protect and reinforce the join, 6 A multistrand auto wire for example.

Or you could just use some flexible hook-up wire and run out two or more radials on the day. Less weight and easier to wind onto a kite string winder.

Good luck.

73
Ron
VK3AFW


#12

You might find “antenna wire” handles better. I used figure of 8 stranded bell wire for years, and it was easy to handle in warm or cold weather. When I ran out of that, I bought some cheap speaker cable that looked much the same. But, in warm weather it is limp and determined to tangle, and in freezing conditions it is like spring steel! Not all insulation material is equal, and finding something that works for you can make life easier.

Cat 5 and 6 patch leads usually have stranded conductors, and come in usefully long lengths…


#13

Hi Ron,
James mentioned that the CAT-6 was a “left-over” from a project and hence cost him nothing - I guess this falls into the usual Ham Radio adage - use what you have - especially if it cost nothing.
The fact is that James saw success with just two radials - perhaps you should add another two for the next test James? It’ll be interesting - especially if you can hook and unhook the two new radial wires to see what difference having 4 as opposed to 2 cable runs will make.

If you have, or can borrow an antenna analyser, itwould be interesting to see if you trim them to resonance whether you gat a further improvement - but as already mentioned, the ground the wires lay on will also affect the resonant length.

If you can raise the vertical off the ground and have the radials go out above ground to their ends (where they can be pegged with plastic pegs you could also see an improvement in performance.

Quote from my Amateur radio instructor where I took my course for the UK licence, many, many years ago - “Antennas are not a Science - they’re magic and can work in very strange ways sometimes”

73 Ed.


#14

especially if you can hook and unhook the two new radial wires to see what difference having 4 as opposed to 2 cable runs will make.

My experience is that 2 vs 3 or 4 radials don’t make a big difference in performance, although the risk of current on the mic is much higher when having only 2 in a SOTA setup where you usually sit next to the antenna. This applies to elevated ground planes, wouldn’t use a real ground plane antenna with only two radials anyway.

Ahoi
Pom


#15

G’day Ed,

I missed the bit about free cable. Can’t get much cheaper than that.
The wires can be stripped out to make good HF baluns BTW.

Not much magic about antennas these days (except that they work) as with all the right data you can predict what will happen. Gains, patterns and so forth are all codified now.

One radial is the minimum you can have; it is in effect the other end of the dipole. Two radials makes the pattern more symmetrical and raises the efficiency. Both theoretical and practical studies have shown that for ground radials, efficiency improves up to about 20 radials. By then they can be a bit shorter than a quarter wavelength.

I would never deploy that many radials on a summit - too time consuming and a possible tripping hazard.

And you are right, three of four elevated radials are enough but half a metre off the ground isn’t what could be classed as elevated so although the ground conditions have a reduced effect the low radials still couple into the ground and if there are too few the efficiency suffers.

But the low radiation angle of a vertical with a few radials should give better dx performance than a dipole at the height of the top of the vertical.

Local ground conditions and outlook to the horizon are all factors which as SOTA operators we can mostly only guess at until we get on site.

73
Ron
VK3AFW


#16

That’s a nice precis of verticals and radials Ron. Three or four off the ground a bit seems to be a sweet point in better performance of the antenna and ability to set up in the field for SOTA.


#17

Ta,

Could you get the artist known as Christo to wrap a few SOTA peaks in aluminium foil.? Spectacular in the rising and setting sun. And it defines the ground plane. Hmm maybe its getting close to bedtime.

73
Ron
VK3AFW


#18

Can anyone comment as to whether the number of radials (presuming a minimum of 4) affect the bandwidth of a vertical antenna ? i.e. if I add another 4, 3m long non-resonant radials to the existing 4 am I likely to see a change in the range of frequencies where a low VSWR is displayed and if so in which direction? Narrower bandwidth but lower VSWR or wider bandwidth and the same VSWR as at present.

Or no change at all by increasing from 4 to 8 radials?

73 Ed.


#19

That is an interesting question. I would think that radials are probably the low-Q part of the antenna already. The sharpness of the resonance would be dominated by the high-Q element, the vertical part.

wunder


#20

Hi Ed,

Assuming you mean 20m or higher frequencies, adding more non resonant radials may improve the swr bandwidth of the antenna, as it should increase the capacitance of the ground mat to the actual ground. If the ground is rock, it is possible no difference will be noticed.

Replacing the non resonant wires with at least 2 or up to 4 elevated resonant radials would improve the antenna far more than any of the non resonant wires will.

73 Andrew VK1DA/VK2UH