PTT for this transverter is +12 volts (as done with the TS-930S) on pin 6. The interface to the transverter is through a DB9 connector. I just had a lot of 2N7000s and thought I’d save the BS170s in case I ever burnt one in the RXTX. KB9YIG ships the Ensemble RXTX with a couple of spare BS170 FETs that can be used in place of the 2N7000.
So, here is the modification that I came up with using parts I had in my junk box. It also meant that I could operate the radio as designed if I simply disabled the the second T/R switch and connected the antenna to the default port. This meant that I would be assured of having a reasonably clean signal to work with if I configured the radio correctly. The big advantage, though, is that the radio could be operated at its design output and run through a fixed or step attenuator on the TX side to the transverter. This had at least two advantages, the first of which was being minimally invasive. So, I elected for option three, which was to install a second T/R switch at the antenna jack (golden circle). By this time, I was looking for a way to avoid butchering the original circuit too much. The second alternative I considered was the red Xs…jumpering over the BS170 PA transistors. Unfortunately, these locations on the actual printed circuit board were not easily accessible to miniature coax and this process would involve significant surgery to perform and restore the modification. So, I had a look at the RXTX schematics ( here, here, and here) and considered the following options for where to break the RX and TX portions of radio:
Split-IF is the standard for high-performance transverters on the 50-, (70-), 144-, 222-, and 432-MHz amateur bands. This is a pretty simple modification that converts a SoftRock Ensemble RXTX SDR RF interface board from “common-IF” (RX and TX share the same antenna port) to “split-IF” (RX and TX have separate ports).
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