Digital Modes Meanderings
The Equipment – Part 2
The computer side of the digital mode station was taken care of, so it was time to move on to the radio side of things. The selection of radios to use was rather limited really. I had an Alinco DX-70 TH mobile rig and a recently acquired Yaesu FT-901DM. The Alinco was purchased new for six meters mobile operations. It never made it to my truck for that purpose. It proved to be such a good performer overall that it took over the spot that my Kenwood TS-830S had previously held on the radio bench. The TS-830S was a great radio but feature-wise the Alinco blew it away. The TS-830S was traded away for another piece of radio equipment. The Yaesu FT-901DM was an incidental acquisition from a Silent Key (passed away ham) estate sale. There was a Heathkit SB-221 HF amplifier that I really wanted. I was forced to take the Yaesu as well in order to get the SB-221. The estate seller would not split the pairing, so the FT-901DM came home with me. Later, the FT-901DM would be sold to offset the cost of the SB-221, but before that happened it was destined to play a part in my entry into the digital mode world.
So it would seem that the obvious choice of radio for digital mode use would be the Alinco, correct? However, about this time I had some strange problems with the DX-70TH and I sent it off to the repair depot. The Alinco ultimately languished at the repair facility for about two months. Later, I would discover that there had never been any problem with the Alinco, but I digress. That left me with the choices of the FT-901DM or nothing. Okay, so there was no choice, it was the Yaesu. For those who don’t know anything about the Yaesu FT-901DM I need to give a quick rundown of the rig. It was what now days would be called a hybrid radio. It had vacuum tubes for the driver and finals and everything else was mostly discreet solid-state components. Knowing that PSK31 is a relatively high duty cycle mode (around 70%), I was a little concerned about how tubes were going to handle that load demand. Surprisingly, it seemed to do okay, but I was real happy to shift to the Alinco (for several reasons) when it came back from the repair depot.
The computer side of the digital mode station was taken care of, so it was time to move on to the radio side of things. The selection of radios to use was rather limited really. I had an Alinco DX-70 TH mobile rig and a recently acquired Yaesu FT-901DM. The Alinco was purchased new for six meters mobile operations. It never made it to my truck for that purpose. It proved to be such a good performer overall that it took over the spot that my Kenwood TS-830S had previously held on the radio bench. The TS-830S was a great radio but feature-wise the Alinco blew it away. The TS-830S was traded away for another piece of radio equipment. The Yaesu FT-901DM was an incidental acquisition from a Silent Key (passed away ham) estate sale. There was a Heathkit SB-221 HF amplifier that I really wanted. I was forced to take the Yaesu as well in order to get the SB-221. The estate seller would not split the pairing, so the FT-901DM came home with me. Later, the FT-901DM would be sold to offset the cost of the SB-221, but before that happened it was destined to play a part in my entry into the digital mode world.
So it would seem that the obvious choice of radio for digital mode use would be the Alinco, correct? However, about this time I had some strange problems with the DX-70TH and I sent it off to the repair depot. The Alinco ultimately languished at the repair facility for about two months. Later, I would discover that there had never been any problem with the Alinco, but I digress. That left me with the choices of the FT-901DM or nothing. Okay, so there was no choice, it was the Yaesu. For those who don’t know anything about the Yaesu FT-901DM I need to give a quick rundown of the rig. It was what now days would be called a hybrid radio. It had vacuum tubes for the driver and finals and everything else was mostly discreet solid-state components. Knowing that PSK31 is a relatively high duty cycle mode (around 70%), I was a little concerned about how tubes were going to handle that load demand. Surprisingly, it seemed to do okay, but I was real happy to shift to the Alinco (for several reasons) when it came back from the repair depot.
Alinco DX-70TH Yaesu FT-901DM
The FT-901DM in my opinion is a terrible choice for digital mode operations mainly from a reception point of view. The receiver was 1980’s vintage and not particularly very selective. It was not designed for separating signals as close in frequency that digital modes operate. Strong signals easily killed the entire receiver passband. There were no real good QRM fighting tools either. To be fair, it was 20+ years old when I got it, so it may not have been operating at its peak performance. However, it allowed me to be active when otherwise I would have been off the air entirely, so it has a good spot in my memory. I did not run the FT-901DM for very long but I did make quite a few PSK31 and later MFSK16 QSOs with it. The take away lesson from this is to try whatever you have available if you are a new digital operator. Everyone has to start somewhere and the early lessons learned will be invaluable later on in your digital mode ham “career”. That is the ham experience in my opinion, learning by doing. Of course, if you can learn the pit falls without “doing”, all the better!
So what was the problem with the Alinco DX-70TH you ask? There was no problem with the Alinco. Later I found out that the filter capacitors in my 20 year old Astron RS-50A power supply were going bad. They were not doing their job of keeping the voltage up during load conditions. In addition, the power leads that I had been using from the Astron to the DX-70TH were also found to be lacking in the ability to sustain an adequate voltage for proper operation as well. Both problems were rectified and helped pave the way to successful digital mode operations. Sometimes problems provide learning experiences that expand your knowledge base. I now monitor my power supply voltage condition much more closely than I did in the past. Lesson learned.
So what was the problem with the Alinco DX-70TH you ask? There was no problem with the Alinco. Later I found out that the filter capacitors in my 20 year old Astron RS-50A power supply were going bad. They were not doing their job of keeping the voltage up during load conditions. In addition, the power leads that I had been using from the Astron to the DX-70TH were also found to be lacking in the ability to sustain an adequate voltage for proper operation as well. Both problems were rectified and helped pave the way to successful digital mode operations. Sometimes problems provide learning experiences that expand your knowledge base. I now monitor my power supply voltage condition much more closely than I did in the past. Lesson learned.
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