I've been experimenting tuning a 10.7mc IF trans to 4.43mc and switching it in place of the xtal for wide band a,m. I ended up doing pretty much as you would, for am I now have a Ta7642 which does a good job of demodding the rf and has agc, it taps off from the o/p of the IF filter, I have a switch that selects am audio from the '7642 and cw from pin 9 of the '3361.
However the filter amp according to the data sheet is for audio not rf and doesnt limit, your schem shows it as a audio filter but all the gain comes from the following transistor gain stage, I've seen them with a switch for narrowing the passband for cw, I think theres a max suggested o/p voltage I think thats my distortion problem. The limiter amp distorts on am badly as one might expect, on cw though it works well, theres no audio so it doesnt seem to ruin things.
I forgot to add the decoupler on the fet front end, I'll try that, hopefully it wont overload the front end. If you look I forgot the bias resistor from the bfo tranny base to +v, and the 33pf load for the IF filter xtal.
CRYSTAL FILTER DESIGN ON LINE FREE
Kinsman Kindle ePUB free online Crystal Filters: Design, Manufacture, and Application Explores fabrication and testing, for those involved in the manufacture and testing of these products, and includes information on specification and applications for those who use them. Yes, interesting schematic, I should have started with that. RTF Get Crystal Filters: Design, Manufacture, and Application by Robert G. Not sure whether I'll just add a couple of varactors / pots for tuning, or add an arduino and a si5351 dds and lcd / rotary encoder, the dds would delete all the comps for the local osc and the bfo as its triple channel. I connected a 33pf to the o/p of the ne602, then through the xtal and finally another 33pf to the i/p of the mc3361, works well now.Ī fine tune for the bfo isnt required, the local osc can be tuned to create a beat tone with the bfo for cw, and for am or ssb (more like dsb) the local can be tuned so the IF is the same freq as the bfo eliminating the beat note, I thought the local osc being lc would drift and create an unwanted beat tone on am after its runs for a a while, but this doesnt happen, maybe the local is being influenced by the IF or the bfo and syncing to it, or maybe the components are good enough to be stable.įor an ultra simple receiver it works very well, there doesnt appear to be much imd, and it goes down to Vlf, bandwidth is just wide enough for speech (not so much music).
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