This is very interesting, thanks! Currently I have another board to take
to power up to 50W.
Rafael
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On 5/29/21 11:41 PM, Howard Fidel wrote:
I had purchased one ( actually several) of those Chinese 70 watt
linears. They use IRF530s for the RF transistors. I connected one of
these to my uBitx years ago when I first bought my V3. I used it
exclusively at that time on 20 meters and it worked fine, putting out
about 50 watts. I have posted in the past some of my uBitx mods to
improve power output. When I learned about all the intermod product
issues with the V3, and trying some of the posted mods to solve the
problem, I was not successful. It became clear that the V3 was not
worth modifying anymore. I decided to try the Softrock SDR radio. I
modified he Softrock so it could be used on all HF bands, and
connected it the uBitx using the uBitx RF output stage on LPFs and
retaining the Arduino to control the uBitx. The way the uBitx is
designed, it is easy to have a different supply voltage (keep it under
25 volts unless you want to change the aluminum bypass caps). I
changed the IRF510s to IRF520s and increased the output amplifier
supply voltage to 19 volts. With this configuration, I have up to 52
watts rms output. I think that the same output and LPF filter
modifications can be made on any uBitx and provide a similar output
power. The only caveat is that the Softrock has 1 watt of drive. I am
not sure how much drive power the uBitx provides to the final, so some
additional mod may be required to reproduce the power level I have
achieved, but a think a significant increase in power can be obtained
with the drive as is. I have attached my schematics and design notes.
The output stage is on page 7. With the uBitx, the microphone AGC may
also be helpful. The SWR bridge could also be incorporated.
