15 Jul 2012

500kHz tranverter (Mk 2) breadboarding

This weekend I've made considerable progress with the new transverter for 472 and 500kHz and fully breadboarded a 10W TX transverter.

My objectives are to make the design simpler than the original 2010 design  (no expensive SBL1 double balanced mixer!), produce more power and improve the RX performance. Also I want to reduce the need for special parts such as toroids.

The design evolving is, like all my designs, a mixture of my own ideas and the best from other people. When the design is ready I will put it here and on my main website. I've moved away from 28MHz IF (too high, too much start-up drift) and instead gone to 3.7MHz using a 3.2MHz crystal available from GQRP inexpensively. The TX mixer (none is needed on RX as it is uses the FT817 in split mode receiving directly on MF) is a simple bipolar stage followed by a low pass filter. For the PA I have largely copied GW3UEP's excellent designs for a 25 (and later 100W) amplifier. Initially I am using an IRF510 from 13.8V and getting around 10W RF out. The next stage is to look at the RX front end. I want a little gain ahead of the FT817 but with good large signal handling and decent filtering. The FT817 works OK at 500kHz but is a little deaf.

So, a satisfying few hours building.


Gary said...

Nice scope Roger - OS3000 or 3300? I worked for Gould for 20 years. Nice to see them still in use! 73, Gary G0CUQ

Anonymous said...

Looking forward to seeing your improved design. Per 2013 the segment around 470 kHz will be available in Holland as well. Might be interesting for Dutch hams too!

Roger G3XBM said...

Initial TX tests have gone well with the drift typically 1Hz on the old transverter down to zero. Will post schematic here soon.