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Registered Member #2763
Joined: Sat Mar 27 2010, 11:48AM
Location:
Posts: 14
Hello HV maniacs some times ago im experimenting with a prototype FM modulated 8mhz class E coli. I want to reach the best perfomance in most compact pacage. The construction is verry simple Standart class E output amp its driven by simgle IXDD414 + DC blocking capacitor Trace between main transistor and ixdd chip is short so gate signals out is like a square. I added +5V biass to increase the gate signal to +12V and -3V...
FM modulator and oscilator is 74HCT4046
in the first version this project called FlamABLE 1.0 but i have problem with audio mod when i plug jack cable to circuit the signal began to receive a signal from the resonator simple the cable was acting like feedback antena so i must add some filter sections.
in Verion FlamABLE 1.1 the problem is not exist and resonator work perfectly.
Registered Member #1232
Joined: Wed Jan 16 2008, 10:53PM
Location: Doon tha Toon!
Posts: 881
Looks neat. Well done!
You say that the audio modulation is FM, but you use antenna feedback to sustain the oscillation? I'm intrigued how you implemented the frequency modulation with closed-loop feedback?
I did some experimenting with Class-E amplifiers frequency-modulated for a singing TC. Whilst Class-E amplifiers easily handle the small percentage frequency deviation in typical communications applications, you really do need quite a high frequency deviation to produce significant audio output from a TC. After all, FM audio modulation only really works by way of "slope-detection" taking place in the high-Q resonator. You essentially drive the high-Q resonator off-resonance to control the amplitude of the HV at the discharge terminal. And a Class-E amplifier doesn't really like this mismatched condition very much!
What I'm trying to convey is that whilst a Class-E amplifier works great with traditional amplitude modulation, or very small FM deviation in broadcast applications, it gets pulled substantially from it's high-efficiency operating point when using FM to audio modulate a TC.
How much power are you pushing and how hot do things get?
Suggested areas for improvement would be replacing the yellow-white choke core if that's micrometals type-26 for something like a type-6 or type-2 material which is much lower loss. And feeding the TC primary from the amplifier via a twisted pair or coax. You've got quite a lot of enclosed area in those drive wires and they look a little thin to carry amps of RF!
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FlamABLE - Class E HFSSTC 8Mhz
