Yes. I finally looked at the IRF spec sheet and 400W is a little over spec @ 48W a piece. Also the slew rate is pretty limited to a minus 3 dB at 20MHz. So the transistors appear to limit the frequency range as Dale said.Originally Posted by mw0uzo
It is an amazing work though. Good on ya.
Made a lot more progress on the controller since those photos were taken. Got the ADCs working, the 16 bit math working for SWR calculations, pretty power bars, plus some other stuff
Breadboard prototype
PIC: 16F887
Outputs for attenuator control, lpf control, status leds and a load of pots for simulating ADC input.
(The DDS module is a sideproject to write the code to control it)
Main display with detailed status monitor and menu
Main display with power bars and less detail
Some more photos of the build:
Underside in progress
Bias pots and output transformer fitted
Heatsink fitted
Closeup of power distribution arrangement.
There were some issues with this. The closeness of the mosfets and rigid arrangement of the power plane did not allow for slight drilling errors, or placement problems when soldering on the ring connectors, The upshot was failure of the plastic insulating bushes when everything was done up tight and heated up. Next time I would allow a small gap between the mosfets and use braided copper for the power distribution.
Last edited by mw0uzo; 07-25-2012 at 09:39 AM.
How did you compensate for the stray capacitance created by using that "Manhattan" style of construction?
All the world’s a stage, but obviously the play is unrehearsed and everybody is ad-libbing his lines. Maybe that’s why it’s hard to tell if we’re living in a tragedy or a farce.
I didn't
Seriously though, the mosfet capacitance would probably be the largest, small 'd'. Even though there's a big area of copper there for the bias circuitry the 'd' is huge, so it can't be significant amount. I don't actually know though....
If you are building a design for a single frequency, it would be easy. Too difficult to compensate over a large range of frequencies without a different method of tuning it out for each band.I didn't
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