Post by Reverend Bow Voodoo on Mar 3, 2010 10:31:21 GMT -6
Why is it that the Pinnacle of SW pirate AM transmitters, the "Grenade" has never been topped... or at least not produced and publicly announced?
You would think with the technology changes in the last 17 years, someone would have come up with something new and improved.
For example, you do not need a modulation transformer to modulate the final... I know, I pulled the transformer out of my Cobra 29 and modulated it with a Darlington transistor...
Does anyone else have any interest in trying to put something together?
Well the corsair design was low level series modulated and by design should produce HIFI modulation. In my opinion the design is a bit of an upgrade from the original grenade.
It really wouldn't take much to make a quality transmitter but the issue then becomes cost and amount of parts needed which can be too complicated for some people to understand and build in their shack.
What I would probably design if I had the time and parts would be a class E push pull PA stage using a PLL square wave oscillator for the exciter. Modulate it using pulse width modulation (class D). The efficiency of that setup would be great. Almost all the voltage rail would be turned into RF multiplied by 2 because of the LC tank output.
Of course that sounds simple writing it down but in reality it would be a complex design. But at least you'd get a quality transmitter that is designed much like the newest factory assembled transmitters used in real radio stations.
Some simple improvements I would do to the corsair would be to make the output push pull and make the oscillator a tunable frequency synthesizer. The only other upgrade I can see would be going class E. I know a lot of people think the grenade/corsair is class E but that isn't true. They are driving that FET with a sign wave and biased which technically makes it class A which is inefficient and puts the FET under more stress than needed. The only advantage to using class A like that would be the ability of low level modulating it cutting down on modulator parts, and less RF filtering. However the drawback is less RF output power and more thermal heat. But I assume it was designed that way to cut cost and parts used.
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