I'm having lots of fun operating this transceiver. I've worked around North America and even worked a few Europeans. I find it very satisfying to communicate using simple homebrew equipment. I hope it doesn't sound elitist but it definitely has a feel of "real" ham radio about it. The diverse combination of old and new is fun to think about. By that I mean the sophisticated DDS, microprocessor controller, simple direct conversion receiver and of course the ancient thing that makes such simple equipment usable, CW morse code. I usually send with a K1EL WinKeyer.
I'm sure there's a good chance that if had bought a kit rather than going with the all homebrew approach then I would have spent less time, money and ended up with a much more robust and attractive final result but ... I just wanted to do my own thing. There are some great inexpensive kits available in the QRP community and I encourage anyone to take that route if it feels like the right way to go.
40 meters is a great band for CW. There are the DXers at the bottom of the band, the QRPers up around 7030 and 7040 and then there is another group up around 7110. I think that last group is or at least used to be called the technicians' segment even though US technician class licensees can use 7025 to 7125. Slow CW seems to be the norm up at 7110 so it's a good place for anyone wanting to practice.
The performance of the receiver has exceeded my expectations. I get absolutely no "tunable hum" or other typical direct conversion issues with it. I'm lucky in that I don't have any strong local AM broadcast stations. I thought some shortwave broadcasts may have been a problem with the simple single tuned circuit in the front end. There are some very strong signals in the 31 meter band just below 10 MHz but they don't seem to cause me any problems. Your experience may vary. You might need to improve the front end selectivity if you have strong local signals. A parallel tuned circuit in series with or a series circuit across the input could be used to null out a troublesome local broadcaster if there is one particular station causing problems.
The receiver could probably do with an audio gain control. For most signals, I have the RF gain / attenuator barely above zero to avoid excessive volume in the headphones. At times I think it would be nice to turn the AF gain down and crank the RF gain up a bit. I've heard mention of the TDA7052 audio amplifier chip as a good alternative to the LM386. I think its gain can be controlled by a DC voltage level which sounds like a nice simple way to do it.
At times an audio filter would be nice but I haven't really had a problem with the lack of selectivity. As I get older I guess my ears' high frequency response is fading so I already have at least a low pass filter built-in Of course the beauty of a direct conversion is its simplicity. If you try to improve it with lots of enhancements then there probably comes a point when it makes sense to give up on direct conversion and build a superhet with a IF narrow enough to give "proper" single sided reception.
There is definitely room for improvement with the user interface. The most immediate issue is that we need more buttons. I'm thinking of building a new version of the DDS box. I would use a shift register to drive the display as a serial device. That would free up enough pins to have nine buttons in a 3x3 matrix. The extra buttons would allow such enhancements as:
- Easy switching back and forward between 100 Hz to 10 Hz steps. Cycling through all the steps to get from 10 Hz back to 100 Hz is a little tedious.
- A "reverse shift" mode which allows tuning to the low side of a signal to avoid QRM but still transmit on the correct frequency. I can do this now with the RIT by tuning all the way down through zero beat and up the other side but an instant switch would be nice.
I'm sure there are other enhancements but I'm not sure when I'll get to this next step. For now I'm going to get on the air and enjoy some operating.