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BITX Build Update #11 -- Peakin' and Tweakin'
Oh how I love the sound of a newly built receiver! I'm sitting here listening to G0MJS on 17 meters. Lots of other stations from across the pond coming in very nicely.Earlier in the week I had some sensitivity problems. I could hear the noise floor, but just barely. And the receiver just seemed to have trouble inhaling. So I started poking around. It seemed that each poke improved things a bit. I had used Farhan's original schematic (mostly). Later versions put an additional transistor in the IF amp. So I went ahead and added that mod. That helped a bit. Then I noticed that BFO energy was getting into the AF amp. So I put a .1uF cap to ground at the input to the AF preamp. That took care of the RF and did no damage to the AF.
But the rig still seemed a bit hard of hearing. This morning Farhan advised me to take a look at the mixers. I used some junk-box diodes that I didn't know too much about... I measured the forward resistance and found it to be quite a bit higher than the usual 1N914s. So I switched all 6 mixer diodes. That helped noticeably.
I also checked the input bandpass filter. It seems OK. In the process I learned to use the EMRFD filter programs (thanks Wes) and the ELSIE filter program (also very nice).
Anyway, the rig sounds great now. On to the transmitter.
Farhan advises building the power amplifier on a separate copper clad board. But I have room for it on my main board. Should I live dangerously?
Our book: "SolderSmoke -- Global Adventures in Wireless Electronics" http://soldersmoke.com/book.htmOur coffee mugs, T-Shirts, bumper stickers: http://www.cafepress.com/SolderSmokeOur Book Store: http://astore.amazon.com/contracross-20
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