Wednesday, April 12, 2017

A Full Duplex Transverter/Receiver for Satellite Operation

A few years ago I went looking for a dedicated radio to use for mobile and portable operations.  I was very specific about what I wanted: a low-cost, all-mode, HF/VHF/UHF rig, with 100 watt output (at least on HF) and the ability to operate in cross-band, full-duplex mode for working satellites.  After realizing that such a radio doesn't exist, I decided that the only option was to build my own.

I opted to start with a Flex-1500 SDR radio with outboard transverters and amplifiers.  This kept the cost down and after using a Flex-3000 at home as my main HF radio for many years there was no way I was going back to playing "radio blind-man's bluff" with old-school knobs and buttons again.  It's a shame that as of this writing Flex has ended production of the 1500 but it had a nice 12-year run and I expect it will hold its value for quite some time.

The little Flex has a low-power IF port specifically for driving transverters and software support which makes it easy to add other bands.  I found that UT5JCW sells a nice lineup of low-cost transverters through his web site and on eBay.  They fit nicely with my 'low-cost' requirement and I ordered up one each of his 144-28 and 432-28 transverter boards.  Since the transverter boards would be doing all the heavy-lifting as far as gain and front-end filtering goes, I was able to meet my 'full-duplex' requirement simply by adding a little RTL-SDR USB dongle as a sub-receiver.  A toggle switch and a couple of relays to handle the 28MHz IF switching, a few LEDs, a little box to stuff it all into and I'm almost ready to go.

 
View from the rear with the internal shielding removed showing the transverter boards.  The rear panel jacks are for 28MHz IF, KEY in/out, V/U key-out, 12VDC, VHF and UHF.  The slot above the SO-239 connector is for the male USB of the RTL-SDR dongle to stick out.
With the internal shielding in place and the RTL-SDR dongle connected.
The finished product strapped onto the Flex in the portable station.
The transverter boards put out a modest signal (10 watts on VHF and 3 watts on UHF) but since I will be mainly using this with a dual-band vertical antenna the next bit will be to build an 80-watt VHF/UHF brick amplifier to complete the project.  Stay tuned!


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