A Part of the video programme at the 2021 radio conference, this video tells a basic story about the SDR and DSP.

Andrew started by asking: SDR, What exactly is it?, how did it evolve, what are Hybrid SDRs, the Direct sampling limits, and more. He went on to say SDRs are part of the ‘Digital Revolution’. We might want to hang on to old LP records, but the world has gone digital. Take for instance, your phone, camera, TV or even amateur radio transceivers.  The point is that digital signal stages don’t add noise!  SDRs are a logical extension of Digital Signal Processing, or DSP aimed at converting received signals to digital as close as possible to the antenna.

Andrew went on to explain the DSP evolution and how changes were made over time to improve the result.

He explained that many amateur radio ‘DSP’ radios are not actually ‘all digital’ since the incoming signal is too high in frequency to go directly to digital due to direct sampling limits.

Amateurs who are interested in learning a bit more are recommended to watch the video, found at:   https://www.youtube.com/watch?v=jv6DCGa6zy8

A ‘boat anchor’ it is NOT!  This high quality transceiver for 80M runs a cool 400w in Class E and is small and light at only 3kg, including the power supply!  The original design was by Dave GW4GTE and the PCBs and parts were from Eric GW8LJJ. (www.s9plus.com)

Graham explained the amp’s Switch-mode has many advantages, it is theoretically 100% efficient. The audio processing uses a well tailored RMS AGC which controls maximum modulation without the usual heavy modulation transformer. Syllabic compression tracks the users voice power. A very sharp, easily tailored low pass filter keeps the signal bandwidth very well controlled resulting in excellent on air audio reports.

Graham went through each stage of the transceiver to explain how each stage operated to produce the phase width modulated signals with 100% modulation.

The receiver part of the unit is single conversion superhet allowing a choice of 80m or 160m during construction.  No special tools were required during construction but Graham did admit to purchasing an illuminated free standing magnifier (£23). He did, however, use his oscilloscope to set the PWM and drain waveforms. His shack receiver’s display was used for monitoring modulation bandwidth. A most impressive part of this build was the cost, only £347 total.

So, what to add next? CW keying and a BFO, and perhaps add a 160m matching network.

Graham felt it would make a fine addition to the GB2RS news in AM for 80m.

Robert, M0IXM was first to tell about his QCX QRP Kit.. For a start he realised there were many small parts that needed sorting and labelling. These were stored in a small components cabinet. Following the kit’s excellent instructions he soldered in the ICs followed by the resistors which all had to be soldered with one end up as there was insufficient room to lay them down on the PCB. The most difficult part was the winding of the four  inductors and the transformer. That done there were on board tools for alignment and set up. The transceiver worked without problems but the low power didn’t result in any answers. Undaunted, Rob set about sending CQ transmissions to check on the Reverse Beacon Network which showed he was copied far and wide! Success!

Don’s, G4LOO Major Project winner was the coax winder. In the past, after a contest, two persons might be needed, one to hold a pipe fed through the drum plus another to turn the drum and feed the coax on.. Short runs might not be a problem, but several runs of over several hundred feet can be very time consuming as well as tiring.  Don began to think of ways to wind automatically. Finally he settled on preformed aluminium struts to make the frame and a screen wiper motor for power. The main shaft holding the empty drum was made to access several sizes and widths and the motor speed was made variable. The finished project can be moved and powered by a tractor if required. Some photos are shown on 27th of Jan 2022 blog post.

Victor made a genuine Weekend project, a permeability tuned ATU for a long wire. Wanting to make use of a metal container from a Glenfiddich miniature, the project had to be designed to fit inside! The permeability tuner (ferrite rod) just fit the length of the box with two small capacitors to tune it from 40m to 10m, and can handle about 10w perhaps more.

Don started by presenting a dozen titles from the Convention from which to choose. The Radio War was chosen.

The video began with Dr. David Abrutat presenting information from his book, also called Radio War, telling The Secret Espionage War of the Radio Security Service 1938 – 1946. He pointed out that much of the information in public domain centred on Bletchley Park but he wanted to tell the story of the VI operators, who for the most part, remained unknown.

The video can be found at www.rsgb.org using their search facility.