[TowerTalk] Balun question

[Jim Brown]

On 10/10/2021 4:44 PM, David Gilbert wrote:
> 
> 
> Two observations:
> 
> 1.  1500 watts would be about 335 volts RMS into 75 ohms, but peak 
> voltage is about 475 volts.  Presumably the F-connector specs have some 
> margin built it, but still ...
> 
> 2.  I don't think testing at DC is a particularly good indication of 
> what it can handle at RF, especially if you're talking about a 
> dielectric.  i don't know why you would choose that for your test.

And a few more observations. RG-numbers are generic, mostly describing 
Zo and approximate diameters. There are MANY RG6 and RG11 cables, and 
with VERY significant differences from each other. Differences include a 
center conductor that can be anything from copper-clad steel to solid 
copper, a shield that can be anything from a flimsy Al foil with 1-4 Al 
braids to braided copper, and all sorts of jackets.

Likewise, F-connectors come in a broad range of quality levels. Those 
made for commercial installations are FAR more robust than those sold 
for home use.

Years ago, I found a partial spool at local surplus warehouse of a 
Pasternak-branded RG6 that had a solid copper center and two heavy 
braided copper shields. It's construction is quite similar to Belden 
8215. It's significantly larger than the RG6 designed for CATV.

I wouldn't hesitate to use SOME RG11 designed for CATV at legal limit. 
For almost ten years, I've been using 1/2-in CATV hard line for most of 
the runs to two monobanders. It's copper-clad Al center with solid Al 
shield.

I remember W8JI saying that he saw no problem with using "RG6" at legal 
limit. I don't know what of the many types he was thinking of, but my 
impression was that he was talking about one of the CATV variations with 
some form of Al shield. I'm using flooded, CCS, quad-shield CATV RG6 for 
RX antennas.

Another point. Below UHF, loss in coax is all I squared R in the two 
conductors, where R is at the frequency of interest, unless, of course, 
it's degraded in some way, most often by moisture. Loss in an Al shield 
is significantly greater than in copper.

73, Jim K9YC