Thinking of stripping antenna down and restringing it using military twin field telephone cable when the weather improves, at present it's strung with bare wire whereas the other stuff is insulated, what's the approx. difference % wise in length between both...should 2% shorter put me in the ballpark?

I've measured "correction factors" as low as 1% and as high as 5%, depending on the diameter of the wire/insulation etc. I would think 2% is an OK starting point - obviously it's better to be low (wire too long) than high (wire too short)

Steve G3TXQ

When I get around to it I'll replace the 10m elements first using the 2% correction value and see how it goes, if I can get that band right hopefully it's just a matter of carrying the same correction through to the others, either way i'll report back letting you know how I get on.

If you're talking about D10 telephone cable, it consists of a mixture of copper and steel strands.
What effect would the steel have at RF frequencies?

None I hope as I'm banking on the steel strands for added strength and the copper strands doing the conducting, I intend using it in it's twin configuration. I know guys already using this stuff for dipoles and loops and it works the best.

I went from insulated to enamel covered copper and I was about 4% too short but fortunately the wire stretched!
John

You still playing down on Topband John.

Yes 1933 most of the time but I do wander about a wee bit. If you ever need another pair of hands with the aerials give me a shout. john

Antenna now restrung Steve and allowance ranged from 1.5% to 2% depending on band.
For instance original 20m bare driven element was 21.200 and replacement insulated element is 20.876, 17m bare driven was 16.550 whereas replacement insulated is 16.219 and the 10m driven elements worked out that 10.604 was replaced with 10.454.
The insulated wire used was Don-10 http://www.armyradio.com/arsc/customer/ ... uctid=2314

Interesting!

Looking at the spec. the insulation seems to be pretty thick so you might have expected more shift. But I see it's a mixture of nylon and polyethylene, and polyethylene has a much lower dielectric constant that the more usual PVC.

Steve G3TXQ

I thought too maybe added capacitance with it being twin flex might have also accounted in some way for a higher percentage figure but it didn't seem to have any effect.
It's good wire to work with and by god it's strong.