11 Feb 2011

4m transverter boxed and finished (for now)

G3XBM 4m transverter - finished (for now) with 2-3W pep
Another good day today saw the 4m transverter completed and even boxed. I also did the FT817 DC switching mod  to put 5V DC on the antenna pins when on TX. It was easy to do, with care, and made the transverter switching so much easier. Don't understand why it was not there as standard for the sake of 1 capacitor and 1 resistor. The limitations with the current design are:
  • IF breakthrough rejection at 28MHz is not brilliant, as one would expect from a single tuned circuit on the NE602 input. I can change the input to a top coupled pair to help, but will see how it behaves on-air first.
  • LPF on the PA is just a single 3 component Butterworth. At some point I should add another section, but as the drivers/PA are linear all the way through, the 2nd/3rd harmonics should be reasonable already.
  • GB3BAA 4m as received
  • The TX strip has DC power on it even on RX. I need to arrange to switch this off later, but I am not worried that there is another 50mA or so when on RX at the moment.
This evening I have rigged up a horizontal dipole for 70MHz in the loft and am ready to find some locals to work. So far just the 70.016MHz GB3BAA beacon 89km away visible well with Spectran (20dB S/N).

5 comments:

Ian MW0IAN said...

Wow fast worker, well done.Will you publish the circuit on here?

Regards
Ian

Roger G3XBM said...

Hi Ian,

When I have had a few QSOs I will put the schematic on my main website.

73s Roger

Anonymous said...

I am very curious what kind of filter you use direct after the TX-mixer. I am struggling with it now...
73 Ron
pa2rf

Roger G3XBM said...

Ron,

There isn't one directly on the TX mixer output yet. There are tuned circuits in the outputs of both driver stages and a low pass filter after the PA. I've still to check the spectrum on an analyser, which I hope to do at a friends this week.

73s Roger G3XBM

Anonymous said...

Thanks for advice Roger.
I have the RX part of my transverter working now. TX part gives more trouble. Looking forward to seeing your circuit. Within 2 months we will be allowed to work on 4 meters in Holland,
73
Ron
PA2RF