Hi Johan,
Thanks. Fascinating! The modern world, i can just say. I would assume
such a chip is quite expensive and not easy to get in small amounts(?)
Will you build a PA with that chip for the Dreamers Band (TM) and come
on air then? It would be fine! Or maybe a RX station? :-)
All the best and nice to read from you again time sometimes.
73, Stefan
Am 26.04.2016 17:28, schrieb Johan Bodin:
Even more linear QRO for dreamer's band:
http://www.ti.com/lit/ds/symlink/tas5630b.pdf
Den 2016-04-26 kl. 17:18, skrev Johan
Bodin:
Hi Stefan
I thought about your 9kHz PA efforts when I found this class D PWM chip
capable of ~300W up to 100kHz with very low distorsion. Amazing
performance from such a small $6 SMD chip!
http://www.ti.com/lit/ds/symlink/tpa3251.pdf
73 de
Johan SM6LKM
Den 2016-04-23 kl. 18:51, skrev 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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