Sunday, November 22, 2015

Double Side Band (DSB) Generation II

I made some progress with my NE612 DSB Generator. I built it up in a shielded box and I have observed at least a reduced carrier of 20 db below the side bands now. My problem was with my measurement receiver, it was receiving the radiated carrier! I also have attenuated the Si5351 oscillator separately and not in the same box and then injected it into the NE612. Note the 10 db pad. Next I will try a balancing pot across pins 1 and 2 with the wiper to ground. I should be able to get 30 db of reduced carrier with the NE612. The audio fidelity is very good and I believe this will be able to produce eDSB (Extended Double Side Band).

Sunday, November 15, 2015

Double Side Band (DSB) Generation

In my quest for a simple QRP phone rig, I have been experimenting with Double Side Band (DSB) Generation. Using the Si5351 as a local oscillator I have tried both a high level mixer (passive) and a NE612 (active). Both of these produced DSB but with a carrier higher than expected. This was all done on a open breadboard so I believe I am getting carrier leakage. As you can see in in the HDSDR image below I have a very broad DSB signal.

The other test involved here is the fact that I was using my simple Direct Conversion (DC) receiver from my Prototype Radio experiments. A DC receiver normally can not receive a DSB single because of its wide bandwidth causing it to hear both side bands at once. However in the case above, I am feeding the audio from the DC receiver to  HDSDR on my PC. Using the left channel only since the DC receiver does not have a I/Q stereo output (see below the feature in HDSDR).

This method allows the use of a low frequency Intermediate Frequency (IF), in this case 10 kHz allowing the DC receiver with HDSDR to demodulate DSB by receiving either USB or LSB and even ECSS (the DSB feature in HDSDR).

There are other problems with this method like multiple images, however it allows very simple hardware to be used for rigs and I believe two simple DSB transceiver would be able to communicate with each other using this method.