[AMPS] receivers

[Hans Goldschmidt]

1-01-18 08.33, skrev Peter Chadwick på Peter_Chadwick@mitel.com följande:

> 
> Rich says:
> 
>> depends on Webers per cubic meter.  If the output
>> waveform is notably distorted, you have core saturation.
> 
> That generally (but not always) goes with heat in the core, too.
> Of course, tiny cores can saturate at powers so low you don't notice the heat.
> I
> worked on a project once with transformers that didn't produce distortion at
> first, but  as they got hot, the permeability started to drop, and that
> screwed
> up the reflected load impedance, which upset the PA. As the permeability
> dropped
> further, the transformer primary inductance dropped and the transistors died.
> Being less experienced, I got through several pairs of (expensive of course)
> transistors before catching on to what had happened........then just as I got
> things more or less working, the project got canned!
> 
> Ferrite beads as parasitic suppressors (on PA tubes, as well as on low level
> solid state amplifiers) are the most disappointing ferrite application I've
> ever
> tried.
> 
> 73
> 
> Peter G3RZP
> 
> 
> 
> 
> 
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> 
As far as I remember there were several articles regarding this subject in
some old German magazines by Martin. One, I recall, was using Siemens cores
in a sharp a 7 Mc preselector using very high Q Siemens cores. As far as I
remember the intermodulation limit together with Martins high level mixer
was set by the saturation of the cores. I have always been wondering why the
guy did not use bigger cores? Martin also published an article on his high
level front end in Ham Radio and CQ-DL.

In the UKW BERICHTE ( = VHF COMMUNICATIONS) an author ( Krug??) published
several articles on an advanced receiver using different high level mixers
where he went through different kind of ways to terminate the mixers
including intermodulation measurments of crystal and monolitic filters. As
far as I remember he said one should avoid filters using ferrite material.
I may be wrong of course - my memory aint what it used to be at the age of
73.

de Hans SM5KI.


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