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

To: [email protected]
Subject: Re: LF: TXing on VLF again, my first homemade linear PA! :-)
From: DK7FC <[email protected]>
Date: Tue, 26 Apr 2016 21:28:01 +0200
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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:

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!

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

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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