[TowerTalk] Effects of Oxidation on Copper Antenna Wire
lists at oakcom.org
Tue Apr 24 19:08:43 EDT 2018
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?
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