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Re: [TowerTalk] Effects of Oxidation on Copper Antenna Wire

To: towertalk <towertalk@contesting.com>
Subject: Re: [TowerTalk] Effects of Oxidation on Copper Antenna Wire
From: Steve Maki <lists@oakcom.org>
Date: Wed, 25 Apr 2018 09:14:58 -0400
List-post: <mailto:towertalk@contesting.com>
On 04/24/18 19:08 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?

Something just occurred to me - the PIM source might be at the connector(s), where you don't have a solid connection to the foil but to the braid. Even PPC compression fittings merely grip tightly the braid.

-Steve K8LX
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