This project is the culmination of nearly 50 years of plans to build a homebrew radio. When the G2DAF designs came out I desperately wanted to build the receiver but time and lack of money got in the way. Now I have the time but still have little cash!
I owe some thanks to Eamon Skelton EI0GQ for his ‘Homebrew’ article in RadCom particularly the current series on the HF transceiver project. Also, to Jan Verduyn G0BBL for his PPLL VFO. And not least to Roland Hall who kindly gave me a 20m CW transceiver some 10 year back.
Brief specifications: coverage 80m-10m, CW TX, multimode RX, power out 5W max, best RX performance possible, SCAF filter on the audio, as small as is practical.
As it stands the RX consists of several modules that were originally built into tin plate boxes which have begun to corrode. Some will be changed for new ones, the mixer and maybe the IF stage, but in general I need to save space so may stack the PCBs between layers of double sided copper clad board. From the photograph below you can see that the boards are just strung together on the bench and are working perfectly.
(Click to enlarge image click on image to close.)
As mentioned the RX section is lashed up on the bench and working very well. The SCAF filter is superb and does not justify a new crystal filter or attempts to modify the existing one which 3 kHz wide and a superb design. That also means that SSB can be copied easily and from the tests I have done the audio quality is superb, the best I have heard for many years.
The PPLL VFO (SDR-Kits stand alone version) has the IF shift programmed in, currently ~9 Mhz higher than the RX frequency. There is also provision for automatic band switching. This will need a demux and relay diver chips. The output will drive the relays on the band pass filters. I have made one test BPF and it works well. I also tested the RX without a BPF attached and it will work on all the ham bands from 500Khz to 146Mhz with a pretty much flat response i.e. -60dbm giving S9 on the meter which has not yet been calibrated. It would not be possible to make the transceiver work below 80m as the lower frequency limit of the VFO is 3.45Mhz.
The TX side will use the direct output from the PPLL VFO. It should not be that difficult to make a broadband amplifier and a 5W PA stage and Emanon Skelton has already included some stages in his recent articles.
So, what next? I am awaiting the toroids for the 8, BPFs and look forward to hours of winding them. (Not!) The BPF module will then be put together. The band switching module will need to be built on matrix board and the BPFs wired up for a test. When that is done it will be time to start boxing up the modules and seeing how much room is left for the TX. I will post some photographs of the progress.