[TowerTalk] Effects of Oxidation on Copper Antenna Wire

[Grant Saviers]

Interesting data.  One reference I found discussed the dramatic increase 
in PIM from motion induced rubbing of coax braid strands, although again 
unlikely an issue at HF.  Thus one might suppose a bare stranded wire 
dipole might generate PIM in a wind.

Grant KZ1W

On 4/24/2018 14:45 PM, Steve Maki wrote:
> On 04/24/18 17:03 PM, Grant Saviers wrote:
>
>> Andrew published some research that shows the PIM (passive intermod) 
>> differences between braid and solid copper shields for coax.  I 
>> couldn't find that pdf on the web, but it shows how braid generates 
>> more IM products than solid Cu tubing.  I think its pretty 
>> insignificant for HF ham radio.
>
> Mostly true. For HF it's insignificant. For UHF and above it's 
> insignificant for receive only or simplex. For UHF duplex (repeaters) 
> I *think* it can be significant. LMR style cables have very poor PIM 
> performance (like 25 dB worse or more) compared to Heliax/hardline 
> style cables. I've measured PIM on LMR400 & LMR600 at 700 MHz and 
> above, and it's horrendous by cell service LTE standards (which is 
> -143 dBc using two 20 watt carriers).
>
> Kinda surprising given that the *RF* foil shield is solid for all (or 
> most) practical purposes.
>
> -Steve K8LX
>
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