2m to HF transverter

QSO with the finished transverter using Yaesu FT757GX I added two records together. OH1MN recorded my audio with his equipment (FT-897) and I recorded his audio with my mine (transverter + 757).

Click the image below to view a series of pictures related to this project

Intro:

I already had this really nice 2 meter radio for FM, the computer controlled Mobira RC25, but I was missing something, the SSB!!! I also had build the 2m/70cm dualband quad antenna so all the other necessary equipment for long dinstace DX QSOs existed, besides the SSB mode. One option, which turned out to be the best one for me, was to build a transverter, so that I would be able to use my HF radio as an intermediate frequency radio and later add this inside my homebrew HF radio to have HF/2m all mode radio.

Building the receiver section of the transverter:

I found many sites about homebrew transverters, but only few about 2 meter to HF versions and none of those were good for my purpose. This was my chance to design and make my first a little bit more complicated RF project. I have hobbied electronics really long time, but never designed any really complex RF circuits. This was my first shot! For RX I desided to use 32 MHz TTL DIP crystal oscillator for the local oscillator, because of it's great harmonics. I had to make a plan about the dbm needed and bandpass filtering to cut out the left over frequencies. The fifth harmonic was the needed LO frequency (160MHz), so I would have intermediate frequency of around 14 to 16 MHz. See the block diagram

I decided to use Mobira RC25 receiver's front circuit that has the Bandpass filter, preamp and first mixer sections on the same board. Those were easily available here, so there was no sense to build equivalent system. So basically all I needed was the local oscillator. This LO had to have somekind of switching system so, that I could use it on both, RX and TX. I realized, that the best way was to use PIN diode switches that are fair simple to construct and cheap too. I add simple inverter switches so, that providing +5 or 0 to the board, I was able to change PIN diode outputs from RX to TX.

Testing the receiver

The first test was a dissapointment. But after I realized that I forgot something and fixed it (I don't dare to admit, hi), I couldn't stop smiling. The thing "worked as the toilet of train" (typical dictum used in Finland. In old days, Train toilets used to drop the "stuff" straight to the railroad when pushing foot operated simple flap switch). I tuned the thing and had a chat on FM over 2 meters with OH1MN Markus, while I listened to the transmission with my HF radio at 14 MHz with this converter. Markus sent me test transmission on SSB. Here you can hear the recording of it. Great sound, ehh?

Building the transmitter section of the transverter:

Since the LO board had two outputs, it was easy to continue to the transmitter board. I desided to use SBL-1 mixer because I had few of those at my junk box. No termination or attenuation/amplification was needed for the LO signal because the output just happened to satisfy SBL-1 mixers needs. From IF output we got 160MHz-14MHz = 146MHz and 160+14MHz = 174 MHz so it was necessary to use bandpass filtering. After few Bandpass filters and amp stages I had signal strong enough to drive the 2 meter PA which was originally ment for 2 meter FM but worked really fine after biased properly to a class A. OH1MN once again, kindly recorded my transmissio on both, FM and SSB. So this recording is the FT757 through the transverter (first FM then SSB).

Final Words:

Oh my, if just all people would realized this feeling when you succeed in something like this. It is a great feeling that saved many bucks :)