HFU HF Underground
Loggings => North American Shortwave Pirate => Topic started by: Ron - Calif. on October 16, 2023, 2053 UTC
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6200 AM - For a long time I had not been hearing any Hikari FM (pirate) signal and assumed he was having transmitter
problems. Then on both Oct 15 and 16, I heard an open carrier with good signal strength (0450+ UT). Sent an email to
the operator of Hikari FM, inquiring if I was correct in assuming he was testing again. Here is his reply, with the good
news that he plans on returning to the air before too long with actual audio.
"Yes, I am having problems with my amplitude modulator. I need an audio amplifier to modulate it. The previous
modulator got very hot and it was very inefficient which led to its failure.
Right now the setup is a modulation transformer and I am building a class E audio amplifier. This setup allowed me
to step up the power a little. The carrier is on because I will be doing some testing and pretty soon will be back on air
with music. This is if all goes by plan.
There is a lot of new music that will be coming and another reformatting with now separate time for electronic music
and another time for Jpop. Thank you very much for your support! Best regards."
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Not sure what he's doing but don't believe you can use class E for audio, class D maybe?
Dont know the power levels but class D modulator for 500W is around an inch sq and barely gets warm as eff is 95+%.
Can you provide more info.
Str.
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Class E is wholly inappropriate for a modulator. He will be unable to make it not sound unrecognizably horribly distorted. Class E is not intended for audio amplification. No one uses Class E for audio for this reason. I assume he means Class D, which is widely used for audio and is appropriate.
I want to be encouraging and not haughty but I have been casually watching what he has been been doing and I'm going to suggest that at his level of skill and knowledge that building a Class-D amp is a bit beyond even slightly uncomfortable reach for him. I'm doing one now for myself and there are numerous potential pitfalls, just as there are in RF design. Recognizing those pitfalls ahead of time and coming up with solutions to the pitfalls that you didn't catch requires a certain depth and experience. I suggest buying a regular Class-D audio amp and using it instead. At his TX power level, they are completely appropriate. They are very inexpensive and bound to be a lot less frustrating for a beginning experimenter. Many of us on here, including me, have done this for various projects to save a lot of work and time.