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Re: [TowerTalk] Feedline (choke) question

To: towertalk@contesting.com
Subject: Re: [TowerTalk] Feedline (choke) question
From: Steve Harrison <k0xp@k0xp.com>
Date: Thu, 2 Oct 2025 10:47:48 -0700
List-post: <mailto:towertalk@contesting.com>
On 10/2/2025 9:35 AM, Jim Brown wrote:
On 10/2/2025 7:55 AM, Steve Harrison wrote:
However, it is a fact that connectors of the 1/2"-size (which includes UHF, type N, and even type C with their extra-thick center pin) do heat up when a kilowatt or more is passed through them, particularly at V/UHF.

Have you observed this issue with top quality connectors?

This was a commercial application, and our customer was a well-known governmental agency; of course I used (and the company and power combiner manufacturer paid for) the best available: silver-plated Amphenol as well as some Suhners in several other places. And as I mentioned, the agency's techs later showed me failed formerly-silver-plated Amphenols (they burned up, so the silver-plating was flaking off some of them). We did not, however, go as far as to spec gold-plated: I don't know whether such was even available at the time, unless you could specify space-qualified components.

That was not the issue: the real issue was the thermal expansion and contraction of the connectors causing the connectors to loosen over time. We are talking about connectors that passed a kilowatt at 450 MHz heating up, then cooling off suddenly as they were near or within the cool air-conditioned stream from the rack's environmental systems.

When I told my dad about the problem, he mentioned that at one time, TRW was experiencing trouble with spurious radiation in satellites that was eventually traced to some coaxial connectors in birds. As you know, most commercially-available type SMA connectors are (or were, back then) stainless steel. They had to quit using those and switch to wholly-gold-plated coaxial connectors everywhere. That problem was due to minute galvanic corrosion between dissimilar connector materials that caused micro- diode junctions between connector interfaces, causing microwatt-level spurious products even at very low transmit powers. The present stories circulating about the spurious radiation from Starlink birds that can be easily-heard on ground receivers makes me wonder whether they made the same mistake. All over again  8-).

I have also heard of big multi-multis experiencing connector generation of spurious products due to poor or loose coaxial connectors, which can result from thermal expansion/contraction. Dissimilar-material coaxial connectors can also cause problems; I remember reading of one in New England that took the station operator SEVERAL YEARS before he accidentally ran across (and cured) the real source of the spurious products that had plagued his operators for years.

Steve, K0XP


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