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Hellschreiber beacon - with some oomph!

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Radiotech:
I decided to try to use the El Pititico transmitter as an oscillator for a project with some more power than the 750mW i got from the last one. QRP-Labs has a nice HF-amp with an IRF510 that i would like to try.

To get more stability from the oscillator i powered it down to 8v, about 400mW. The voltage will be higher for the PA, to get more RF output. Does anyone know if i should keep the low-pass filter after the oscillator? Or is it enough with the one after the power amplifier?

Also i am redesigning the enclosure, there will be some more heat to dissipate with this alteration, and i need space for more components.

Teotwaki:
Keep the LPF after the oscillator. No need to amplify the oscillator's harmonics and create other byproducts in the PA stage.

Radiotech:
The circuit is now ready for bias adjustment, and then to do some testing on RF-output vs voltage. There are two voltage regulators on board, 5v for mosfet-bias and the micro controller, and 8v for the oscillator. I got a 0-30v 3Amp power supply, that makes things a lot easier when testing these transmitters.

Im using a T50-43 10T bifilar transformer to the RF-output, it is supposed to impedance match the IRF510 to the 50ohm antenna.

The 400mW drive should be enough, according to the author of the document above, about 500mW is needed to fully drive the IRF510.


I found this http://www.iw3sgt.it/IW3SGT_PRJ/IW3SGT_AMP_LF/ClassDEF1.pdf that describes the different amplifiers in a very easy and understandable way. Its written by NA5N, it made me understand amps better.

Radiotech:
The IRF510 amplifier works, i get sort off a wave form ;D

Running the oscillator at 8V gives an output of 81vpp. The oscillator puts 16vpp into the gate of the IRF510, and i adjusted the gate bias to just where it starts to draw power.



At first i got no power out from the amp, after a while i discovered that i had wound the T50-43 bifilar 10T the wrong way, once that was solved it worked better!

Radiotech:
I made a 5.th order chebyshev low-pass filter to filter the output, it made the signal look a lot better, but its still not very good looking. Should i use a filter with more components?

I did expect a bit more output power, with 30v of supply i get approx 5,5Watts of output after the low pass filter.

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