[UK-CONTEST] Cables

[David, G3YYD]

Been watching this along with the hard-line thread with interest.

The thing to keep in mind assuming copper is used for the cable and the 
outer is 95% coverage or better that the loss of the cable is 
proportional to the circumference of the inner. So using a lower average 
dialectic value for the inner/outer separator results in a fatter inner 
with larger circumference i.e. less loss to maintain the same cable 
impedance. The other way of reducing loss is to increase the size of the 
outer diameter and thus the inner circumference. Of course a fatter 
cable means lots more copper for the outer and for the inner so lots 
more cost. In the end it becomes a trade off between loss, cost and 
benefit.

The loss in the dialectic separator is virtually zero compared to the 
inner conductor loss.

I actually use RG58 to feed my 160m antenna but then it is only 2 metres 
from my remote antenna switch which is fed with 8 metres of W103 from 
the TX. Using anything fatter on 160m from the remote switch would be a 
waste of cost apart from the fact I had a spare length of RG58 with 
connectors on anyway.

As for us UK hams, we are licensed by the power delivered at the antenna 
not at the TX output. My amplifier output can overcome the coax loss 
unless I was using RG58 on 2m then the coax would fail due to the heat 
from the inner conductor melting the polythene inner/outer separator. 
The skin effect at increasing loss with increasing frequency is a 
reality, which means some very high powered coax uses copper tube or 
copper plated steel for the inner to reduce cost.

With the dramatic drop in raw copper prices towards the end of last year 
should see coax prices come down later in 2009 after the current stock 
is replaced with newly manufactured stock. It may be worth while waiting 
a while before buying new coax. How do I get access to those with 
remnants of  Andrews or similar type coax to dispose of?


David G3YYD