|direct conversion receiver ,20 meter|
After finishing the direct conversion receiver based on the xtal oscillator 14318kc it is time to update it to the fully dsb/cw capable radio. Finished the brewing and following points observed....
1. There was hum in the radio may be due to the local qrm or band conditions. when computer was running nearby it disliked it and produced unbearable noise.
2. High gain pre-amp was not quite. i used bc 549c , it needs to be a quiter variety like bc108.
3.shielding of vxo is a must, as tuning is relatively sharp. I doubt without slow tuning vfo this type of rx can be difficult to tune-up for ssb.Here vc-gang provides enough slow tuning freq spread is about 3kc. Lower limit reached by L and higher limit by c.
4. Front end BPF needs to be a slug tuned core type or may be with air core coil but with a variable capacitor to adjust the bandpass characteristic. In the first receiver bpf was the problem. After putting this bpf all sw/am breakthrough deminished.
ckt will continue.....
Circuit is put into the box. Also a closeup view of the VXO is given how the variable capacitor is fixed with body.
Re-tuned up the rx and works ok for a CW morse practise receiver. I dont recomend it for a day to day serious use. As i was designing the TX based on the xtal a companion receiver was needed. I cant subject my main receiver to unruly transmitters harsh signal, so this was conceived. A good RF BPF filter needs to be designed and put, so that am breakthrough does not come !
|VXO close-up look|
|Inside view of DC Receiver|