[TowerTalk] Effects of Oxidation on Copper Antenna Wire

[Steve Maki]

On 04/24/18 18:53 PM, Jim Brown wrote:

> On 4/24/2018 2:45 PM, Steve Maki wrote:

>> 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.

> I suspect the issue may be degradation of the contact between the foil 
> and the braid. In one of the later editions of his book on Interstation 
> Interference, W2VJN noted significant degradation of some stubs built 
> with LMR400 that had been in his garage for years.

I was measuring new cables. In any case, my understanding is that what 
is outside the shield should not matter, unless it's a common mode issue?

-Steve K8LX