Could a Hackaday Lurker pull this off?
I have always had penchant for Ten Tec Radios and when I spotted a Ten Tec Model 150A commercial radio an idea came to mind. Why couldn't this 8 Channel, 2-12 MHz SSB/CW transceiver be modified for the lower ham bands? I found one on eBay and the cost was $99. Heck if it was a bust the parts alone would be worth $99.
This is not a project where you can simply heat up the iron and solder a few parts and you are there. It is a project where you need the manual, and you need to understand how the radio was designed and intended to work.
The stock 150A covered 2-12MHz with a 12MHz IF and operated USB. The BFO/Carrier Oscillator was at a fixed frequency and to add LSB requires a second filter. Drake (and others) did this in the TR-3/TR-4. I could not find the LSB filter so with a bit of Arduino/Si5351 magic I was able to use a single filter.
I ran across a ham who worked at Kachina and he had a set of 16MHz USB/LSB filters which he suggested using in the TT 150A. I tried that approach but the 16MHz scheme would need a bit more work on the internal networks. Since the Model 150A already had much of the heavy lifting done, I stuck with the single 12MHz Filter.
My study of the circuits clearly showed that it was not just a simple matter of ripping out the Crystal Oscillator circuits and popping in a boring Si5351 for there were Tuned Networks that required modification and adjustment.
Let me explain. In addition to the 8 Channel selection switch there was another 8-position switch to select the proper range of low pass filters. In between were certain other filter networks to assure that what was selected was indeed transmitted.
In this posting I included the LT Spice Simulation of the network following the Receiver/Transmit Mixer stage. I was blown away that one network could pass such a broad band of frequencies. Try that with your precious Nano VNA. It appears that the network is a cascaded Low Pass and High Pass Filter that results in a really wide range Band Pass.
The 1st problem with this network was that it indeed cuts off at 12 MHz, so we had to play with the circuit constants to extend that to slightly beyond 14 MHz.
Copy this circuit as someday you might want a wide range band pass filter -- like on a front end of a receiver.
In passing the Drake TR-7 uses a similar cascaded LPF/BPF approach with a twist. On receive they are connected directly, but on transmit the High Pass which comes 1st is connected to the input of the RF Brick and the output of the high-power stage is connected to the input side of the Low Pass Filter. Some very expensive high power PIN Diodes do signal steering!
I am posting this because of what I have seen with those hackaday lurkers that make disparaging comments about individual projects. This conversion took engineering skills and the ability to look beyond a GitHub listing. So, hackaday lurkers let us see your work!
Always slightly ahead of the curve.
73's
Pete N6QW