[TowerTalk] Balun question

[David Gilbert]

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.

73,
Dave   AB7E





On 10/10/2021 3:37 PM, Gary wrote:
> Carol,
>
> 	I believe I am one of the authors of the April 2021 QST article you referring too. I would have never thought to run high power through a type 'F' connector, and was a little surprised at what they are capable of when I read the specs available halfway down the page here:
> https://www.amphenolrf.com/connectors/f-type-connectors.html
>
> A back of the envelope calculation says legal limit Voltage in a 75 Ohm system would be around 335 Volts with a perfect match. Below the 400 Volt rating of the type F connector (I'm surprised), but that's cutting it close in my book.
>
> As for the baluns -- We tested all the ones we built at 1000 Volts DC and did not see any arcing, or measure any appreciable leakage. Dave (N0DL co-author) has access to a lot of neat test gear as part of his job. I would recommend you take special care to not kink or over-work the coax, and keep the passes through the core as spread out as possible.
>
> I hope this helps a little.
>
> 73,
> Joe kk0sd
>
>
> -----Original Message-----
> From: TowerTalk <towertalk-bounces at contesting.com> On Behalf Of CAROL RICHARDS
> Sent: Saturday, October 9, 2021 2:14 PM
> To: Towertalk at contesting.com
> Subject: [TowerTalk] Balun question
>
> Hello all,
>
> I have two questions which I hope someone will be able to answer...
>
>
> 1. I have acquired a large supply of 75 ohm ( aka RG 11) CATV hardline from the local CATV company. They were even kind enough to install the F-fittings for me. I have enough F-PL259 adapters to use with the cable. Will the CATV fittings handle 1kw on 80m and 40m inverted vee's?
>
> 2. I built several 1:1 Current Baluns from the April 2021 issue of QST and they work fine. The specs say they will handle legal limit. Both my 80m and 40m vees are cut for CW. When I want to go on SSB, I usually run the coax through a Palstar AT2K tuner. I never worried about this before since I always used coax chokes, but now I might have some concerns. Although the amplifier ( 1kw) is happy, SWR-wise, I realize that I might have some high voltage that might be going through the chokes and ultimately fry them. Any Thoughts out there?
>
>
> Carol
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