Gang,
I've had a lot of replies with Doug's correct email address. I tried
it and the message didn't bounce. Thanks all.
While I have always received QRPp before the US subscribers even
started wondering when it would arrive (1st class mail for DX
subscr.), this time it looks like I'm not going to be able to decipher
all those stories about thumping NC38s' with the actual schematic in
hand, hi.
I wonder if other subscribers in Europe have received their QRPp yet.
Yesterday I wrote that I had reversed the winding sense of the
secondary of the transformer between driver and PA of my Sierra.
Somebody may have read it and gotten the (wrong) idea.
I thought the transformer was wound the wrong way and rewound it.
Today I had a chance to look at the wave forms on each side of the
transformer with a 'scope. They looked very much like the picture in
the QRP data book (fig. 4-7), but phasing of the new transformer was
clearly wrong. So I had really figured the winding sense all wrong and
the original transformer was OK (except I had the wrong number of
turns).
I find it quite tricky to try and figure out the phasing of a toroid
transformer.
To figure out how the windings on a toroid are phased I think it may
be helpful - in one's mind and in a drawing - to first cut the toroid
open between the ends of the windings, bend it straight and look at
the turns from either end. Both windings are drawn in a plane like a
spiral. Start drawing each winding close to the center and move
outwards. Both windings should be drawn clockwise. As the start of a
winding pick the end which starts clockwise on the core - looking at
it from the end - , whether the turns actually come towards you or not
- it makes no difference. Mark the drawing so that you know which end
connects where in the circuit. No need to draw the actual number of
turns.
>From this kind of picture one can decide the phasing of the turns w/o
getting mixed up like when looking at a live toroid.
The wrong drive phasing was also evident from readings on the power
meter connected to a real antenna through a parallel LC circuit type
tuner. I couldn't get the reflected power as low as it was before I
changed the transformer. The wrong drive phasing created extra
harmonic output power which is not matched to the load and showed up
as a high residual amount of reflected power (ca. 20 mW vs. 1 mW at 3
W O/P).
Fortunately toroid winding is a cheap thrill.
73, OH2ZAZ
Arjen Raateland
--... ...-- -.. . --- .... ..--- --.. .- --..
Finnish Environment Institute, Helsinki, Finland
SAS Support
EMAIL: Arjen.Raateland@vyh.fi
tel. +358 9 4030 0457
fax +358 9 4030 0490
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