[TowerTalk] Feedline (choke) question

[Steve Harrison]

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