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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