[TowerTalk] Fwd: Old Hardline

[jimlux]

On 11/14/19 6:26 PM, jimlux wrote:
> On 11/14/19 6:08 PM, Robert Harmon wrote:
>> Interesting stuff.  I got on the Trilogy website, they have a 
>> corrugated copper outer conductor too.  Can't
>> find loss specs for lower HF freqs.  Also suppliers and cost.
> 
> For HF, the loss is dominated by the skin effect in the shield and 
> center conductor - especially for hardline, which has almost no 
> dielectric.  So the loss will go as sqrt(f).   If the loss is, say, 
> 10dB/ft at 10 MHz it will be 3.2 dB/ft at 1 MHz.
> 
> More details here:
> https://www.microwaves101.com/encyclopedias/coax-loss-calculations
> 
> 
> 


One thing to watch out for - if either shield or center conductor is 
plated, or small enough that it's not "many" skin depths thick, then it 
gets more complex.

However, our trusty friend RG-8 has an AWG 13 center conductor which is 
some  72 mils in diameter, and skin depth at 1 MHz in copper is 2.5 mils.

You can get bit on cable TV coax which sometimes has a very, very thin 
layer of copper on a steel core. At 100 MHz, skin depth is 0.25 mil, and 
it gets smaller as you go higher.

Magnetic materials under the conductor are a particular evil. (steel 
cores, nickle plate under a gold flash..)