开云体育

I have a partial ADC 20 conversion receiver section built but I'm not sure the 9 MHz IF filter is working properly--I don't have any 9 MHz crystals that have much Q, for one concern. I decided to built the ADC 40 receiver section so I could compare voltages and waveforms. I finished it today and it's working properly and sensitivity matches the original (stated in the article as 0.5 uV/-113 dBm). I matched up some 4 MHz crystals for the IF filter--the one I characterized had Q 140k. The VFO is set to around 7030 kHz (fix-tuned). The VFO buffer Q7 is interesting--it "sort of" squares up the sinewave from the VFO--that wasn't mentioned in the article. At 13.0 V supply (shown on the schematic as 13 V), no-signal receive current is 60.5 mA. (I don't have Q6,9,10 installed since I'm just interested in the receiver for now.) I didn't have a 12 uH choke (L3) so wound a T37-2 with 55 turns of #32. The 30 pF trim cap C14 wasn't enough to peak resonance so I added a fixed cap. I used a T50-7 (white) toroid for the VFO inductor L4. I'm using J310 jfets for both sets; 2N4401 bipolars from Mouser.

73,

Steve AA7U