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From: Jeroen Belleman <jeroen@nospam.please>
Newsgroups: sci.electronics.design
Subject: Re: IF transformer VNA Characterisation
Date: Mon, 17 Feb 2025 10:21:25 +0100
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On 2/16/25 21:19, Cursitor Doom wrote:
> When I lived in Germany, I joined DARC (as you do) and showed my new
> sausage-noshing friends some examples of my construction handiwork. As
> a result of that, they gave it a specific German portmanteau term  to
> describe it: Scheissebau. I haven't looked up the translation but I'm
> guessing it means 'ingeniously-resourceful.' ;-)
> Anyway, here's a prime example. I have several hundred broadcast radio
> intermediate frequency transformers manufactured in the early 1970s.
> 
> https://disk.yandex.com/i/Ym1YrWS2YGTnxw
> 
> I was curious as to what IF they were made for. Each of them is
> color-coded to indicate this, but I have no chart to de-code this and
> online sources conflict in many respects. The obvious answer was to
> test them all and create a chart from those findings. This
> necessitated the building of a test fixture to accommodate the
> transformers, which can be plugged into it and swapped around for
> purposes of comparison. Having built this, I then needed to make up a
> calibration kit to establish a reference plane to subtract the effects
> of the hook-up cabling and connections. Fortunately, de-embedding and
> whatnot is no big deal as these IFs are low, so the parasitics (which
> I'm not proud of) in this construction shouldn't materially affect the
> measurements.
> 
> Here's the fixture:
> https://disk.yandex.com/i/NE8B4i5Yh0jWYA
> 
> A specimen IF for testing:
> https://disk.yandex.com/i/BUpamDpN8us8pQ
> 
> The ad-hoc calibration kit:
> https://disk.yandex.com/i/CaV7QGfA-KtP_w
> 
> 
> 

I don't think it's meaningful to use them in a 50 Ohm
environment. They were used as collector loads of common
emitter stages, so were driven by a high impedance, say,
20 kOhm or so. The target load impedance on the secondary
varied according to the specific purpose of the stage.
(I think the ones with the yellow screws were optimized
to drive diode detectors in AM radios, and red ones were
AM band LO oscillator coils.)

Jeroen Belleman