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From: "J. Allen" <vy1ja@northwestel.net>
To: "LF \(RSGB\)" <rsgb_lf_group@blacksheep.org>,
	<lowfer@lwca.org>
Date: Wed, 30 Aug 2006 22:54:49 -0000
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Subject: LF: Scope Manual, Amp questions and comments. my old antenna problem
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Status: O

Hello, Everyone,

In doing the transmitter checks, a scope with two reliable channels was 
needed for the ScopeMatch and for troubleshooting.  The local TV repair shop 
is going out of business and sold me a Hitachi V-680 Dual trace digital 
storage scope for a very good price.

I have the service manual, but neither the operating manual nor the 
specifications could be located through a websearch which was done earlier 
today.

Does anyone have the operating manual or know where a copy can be obtained? 
Hitachi has been contacted and their webpages searched, but they do not even 
show an Oscilloscope.

Any tips or clues would be appreciated.

Also, does anyone know the advantages and disadvantages of using Bifilar 
windings on amp output transformers for Push-Pull amps?   I do not know if 
this is usually the case, but when I used the straight winding method, the 
amplifier ran a lot more power but when I switched to the bifilar winding 
the output waveform has just a little bit less even order harmonic content.

By the way... The amp is working very much better now, with one small 
caveat.

It is also interesting that when the good scope was put in service, it 
became apparent that the channel on the old scope which had been 
intermittent also had been indicating a slightly better antenna match than 
the new scope does.

On the Push Pull amp prototype, there is a small amount of high frequency 
damped wave ringing which occurs just before the positive and negative peaks 
of the amp output voltage and current waveforms.  These damped waves are 
very small, but will they may be a harbinger of troubles to come if they are 
ignored, or are they a normal occurrence in these inverter type amps...  are 
they important?

The output transformer will be rewound from bifilar to conventional winding 
and if it has any effect on the damped waves, I will let the group know.

Thanks to all for the help getting the transmitter working...   There were 
several problems, all related to being in the VY1JA shack... :o)   The main 
problem was that I misunderstood or my memory failed.  I thought the amp was 
set for input frequency divide-by-two and it was set for divide-by-four. 
When the HF rig output was doubled from 13.778 to 27.555 MHz, the output 
waveform of the rig tamed right down.

This explains why I was having those really bad antenna waveforms a couple 
of months back whenever I switched to the prototype amp.  When I build my 
amp shortly, it will only divide by 2 so that I can use the frequency output 
display of the HF rig.  Here too, thanks to all who worked with me to try to 
solve the antenna matching problem.

With a good rig and scopematch in hand, I am looking at revisiting the 
Variometer.  If you remember, I removed it and replaced it with a simple 
single layer tapped solenoid, with a separate link-coupled air-core 
impedance matching transformer.  Perhaps it is due to the size of the 
antenna, but the antenna holds its match well even in rain and wind.  Yes, 
the trace moves slightly around but not enough to require a trip outside.

When the variometer is redone, I am considering winding it with #12 
Thermoplastic insulated building wire,  is there any drawback to this in a 
situation where little inductance is required?

73,

J.
jallen@yknet.ca