Best gauge of wire

Useful information regarding antennas for SDR products.
WV8DOF
Posts: 1
Joined: Sat Oct 28, 2017 12:46 pm

Best gauge of wire

Postby WV8DOF » Sat Oct 28, 2017 12:54 pm

I have a SDRplay2 what is the best gauge of wire to use for a long wire antenna.
Thanks :D
Last edited by WV8DOF on Thu Jan 01, 1970 12:00 am, edited 0 times in total.
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vk3alb
Posts: 17
Joined: Sat Jul 01, 2017 11:43 pm

Re: Best gauge of wire

Postby vk3alb » Sun Oct 29, 2017 2:11 am

Hi WV8DOF,

The most important thing about wire gauge for a receiving antenna is to ensure it strong enough to survive out in the elements without breaking. I use stranded copper wire 7x0.029" strung between trees. It survives for years without breaking.

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Lou
VK3ALB

vk7jj
Posts: 20
Joined: Thu Mar 02, 2017 9:56 am

Re: Best gauge of wire

Postby vk7jj » Sun Oct 29, 2017 6:14 am

As a thought provoking alternative - for several years I've been using aluminium welding wire.

It is inexpensive, is available on small and large reels at diameters of typically 0.9mm and 1.2mm, has high breaking strain, is light enough to use a minimum of supports for large spans, does not corrode and most importantly causes perching birds to fall off :-/

I currently have two seperate full wave delta loop antennas resonant on 160m using it.

Using MMANA antenna analysis program to compare it's resistance against copper and steel for a 160m delta mounted 12m above the ground:

0.8mm aluminium => calculated feed point impedance of 28.69 ohms
0.8mm copper => 27.01 ohms
0.8mm steel => 189.9 ohms

The take away from that comparison is don't use steel!

The precise numbers are given above not as a definitive calculation of the true impedance of my loops but simply to use the built in MMANA metal wire comparison feature, the inference being that the difference between Al and Cu for such a large loop is only in the order of a couple of ohms.

For supporting aluminium wire at the corners of a delta:
cut a 30mm end off some spare 90mm PVC down pipe, tape a 200mm length of thin black cheap 4mm poly irrigation tubing half the way around the circle of PVC, thread the aluminium wire through the tubing, suspend the piece of PVC from lightweight nylon cord. That way the aluminium wire is not bent too sharply (which it hates) and also tension is equalised around your loop as the wire is free to self-adjust

For terminating the aluminium ends:
cut a 400mm long piece of 12mm black poly cheap garden irrigation pipe, drill three holes right through it, about 50mm apart, in each end of the tube. Thread the aluminium wire ends in and out of the holes, the friction prevents the wire from pulling back through, and the flexibility of the poly stops the wire from being bent too sharply. Tie the centre of the poly tubing to your mast with nylon cord, preferably running it through a small cheap pulley so as to easily raise and lower it.

Use simple cheap small brass mains wire joiners to electrically connect the aluminium to your 400 ohm ham or 300 ohm TV twin lead feeder. To prevent electrolysis long term electrical stores supply a suitable tube of paste to squirt into the joiners.

The remaining comment is:
End fed wires suck, they are noisy beyond belief and their impedance swings widely from near zero to near infinity with varying frequency, along with their directivity.

Loops are magic: inherently low noise, nearly omnidirectional, give excellent gain and a lower angle of elevation as the frequency rises.

Hope that helps.

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