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Re: LF: TXing on VLF again, my first homemade linear PA! :-)

To: [email protected]blacksheep.org
Subject: Re: LF: TXing on VLF again, my first homemade linear PA! :-)
From: Markus Vester <[email protected]>
Date: Sun, 24 Apr 2016 10:25:46 -0400
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Hi Stefan,
 
your stable carrier is also well visible on Lubos' and Paul's grabbers. The phase of the first carrier section (16 to 21 UT yesterday, before the DFCW) seems to line up with the rest of the transmission. Noise conditions today are rather poor, plenty of scattered lightning storms around Europe and also occasional local precipitation statics. I'll be gathering data for potential EbNaut emissions but at this time I wouldn't be too optimistic. 
 
Best of luck,
Markus


-----Ursprüngliche Mitteilung-----
Von: DK7FC <[email protected]>
An: rsgb_lf_group <[email protected]>
Verschickt: So, 24 Apr 2016 4:06 pm
Betreff: Re: LF: TXing on VLF again, my first homemade linear PA! :-)

VLF,

The carrier has been on the air from 23:30 to 14:00 UTC, hopefully with a stable phase (no glitches).
I can see weak traces on the DF6NM grabber but all in all it looks quite poor :-(
I'm now trying to prepare for a first EbNaut transmission...

73, Stefan

Am 23.04.2016 18:51, schrieb DK7FC:
Hi all,

Since about 16 UTC i'm transmitting on 8270.00500 Hz again. The antenna current is about 200 mA. It is a first test over a longer time with my new PA.

I have been off the air for a few days now becuase i destroyed my audio amp that i used as a VLF PA. Somehow i started to like the idea of a clean sine wave coming from the PA. Low pass filters are hard to design for VLF, you know. Since i don't like buying and since i didn't find another one in the trash, i 'had to' (actually wanted) to build my own. It is a class-AB PA now running at 20V DC using 2x IRFP064N against ground. Opposite phase drive signals are generated by a small blue ferrite core with 20 quadfilar turns. On the primary side, 2 of these 4 windings are in series. On the scope, the signal looks quite good. The 3rd harmonic is at about -20 dBc, certainly improvable. But it's just version 0.2 now ;-)
A large ferrite core is used to up-transform the voltage to about 220V rms for this power level (i'm not spot on the resonance), also providing galvanic decoupling.

A photo can be found at
https://dl.dropboxusercontent.com/u/19882028/VLF/20160423_184046.jpg
https://dl.dropboxusercontent.com/u/19882028/VLF/20160423_184059.jpg

The PA consumes 3.6A at 20V DC now. Improvements will follow...

The signal will stay on air for a few hours now.

73, Stefan
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