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From: "Don" <g@crcomp.net>
Newsgroups: sci.electronics.design
Subject: Re: Binocular choke extras
Date: Fri, 21 Mar 2025 22:00:24 -0000 (UTC)
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Glen Walpert wrote:
> Don wrote:
>> Glen Walpert wrote:
>>> Don wrote:
>>
>> <snip>
>>
>>> It looks to me that the 3 sections of coax shield are in parallel with
>>> the metal tubes and their opposite end shorting bar, forming the low
>>> impedance single turn winding, to be connected at the unshorted end
>>> with the coax shield connections, hi-Z connections to coax center
>>> conductors extending from opposite end - 4:1 balun?
>>
>> <https://www.qsl.net/kf8od/ldmos1.html> offers a more fleshed out
>> circuit description. The designer designates the device a 4:1 "very
>> broadband transformer."
>>     <https://www.qsl.net/kf8od/ldmos34.jpg> shows the schematic. In the
>> amp as assembled, the transformer output's oriented on the bottom:
>> <https://www.qsl.net/kf8od/ldmos50.jpg>. Everything about its output
>> makes perfect sense to me. The transformer's twin tubular primary inputs
>> shown at the latter link also makes perfect sense to me.
>>     A center tap for the transformer's the thing missing from my mind's
>> eye. Perhaps the shield of the coax cryptically connects the center tap?
>
> Thanks, that clarifies things.  A bit tough to see in the assembly photo,
> but the center tap on the single turn primary is the shorting bar between
> the two metal tubes on the same end as the coax inner conductor
> connections.  I suppose the two 1/2 turn primary windings contribute
> independently to the 4 turn output to provide the stated 1:16 ratio.

My earlier spiel contains a typo. Its last link should be
<https://www.qsl.net/kf8od/ldmos40.jpg>
    One of KF8OD's captions says "the coax is used to accomplish a close
coupling" - presumably to enhance efficiency and performance. It's
apparently OK for the coax shield to bypass the center tap and act as an
ancillary primary.

Danke,

-- 
Don, KB7RPU, https://www.qsl.net/kb7rpu
There was a young lady named Bright Whose speed was far faster than light;
She set out one day In a relative way And returned on the previous night.