R: [AMPS] QRO TORROID (WAS MORE USEFUL SUPPLY.

[Maurizio Panicara]

----- Original Message -----
From: Peter Chadwick <Peter_Chadwick@mitel.com>
To: 'amps' <amps@contesting.com>
Sent: Monday, January 24, 2000 5:23 PM
Subject: RE: [AMPS] QRO TORROID (WAS MORE USEFUL SUPPLY.



> If it's a transmission line transformer, it has to be a very high mismatch
> to screw things up badly. Of course, it isn't a balun, so the balance
> requirements don't exist, possibly easing matters. If it's not a
> transmission line transformer, then all bets are off.
>
> 73
>
> Peter G3RZP

A transformer designed to work several octaves, like 1.5 to 30 MHz  is not a
device free of unwanted parameters. When it's designed for a power circuit,
things become quickly more critical than one could imagine.
Power response apart, who has a suitable network analyzer available can
check what does happen to a  balun (or UN-UN)along a frequency range (mostly
at edges) and expecially if the load has a wrong impedance, actually
reactive.
Verified the performances, until the applied power is not big or the core is
oversized (but larger core size cost more and raise the need of
compensations) the bad effects stay relatively neglegible.
When something instead determinates an higher than predicted core flux, its
not difficult to run out of the pseudo linear range of the core, and things
change more rapidly and significantly than aspected..
Time ago I tried applying 1 Kw @ 28 Mhz to a commercial 4:1 balun, rated
(claimed) 2 Kw, 2 to 50 Mhz.
Well, distortions apart, this balun core did break when I arranged the load
to produce a 1:3 SWR.
Ok, a more serious manufacturer probably does better baluns, but like it or
not a ferrite (or iron powered) core isn't a linear device and hasn't a
linear response.
If the amateur radio market need low cost solutions, in my eyes, a step down
Un-Un is just a compromise.

73,
Mauri I4JMY



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