EMRFD Message Archive 2190
Message Date From Subject 2190 2008-10-06 07:46:15 timshoppa Evolving my multiband LO chain, G3ROO/GM4ZNX PLL, HC4046 vs HCT9046 Had some fun with my new homebrew receiver, using it in a low-key but
still some strong signals contest (California QSO Party, wow, lots of
S9+20's coming in on 40M and 80M from the big guns in California! What
do they have, 80M beams pointed at me?)
Also made some experiments and planning a departure from my previous
plans. Lots of solder used this weekend, and with some luck I'll use
even more over next weekend (3 days!)
My original plan was to mix (DBM) a 3.9 MHz VFO with 6.5, 9.6, and
13.5 MHz crystals to get the 2.6MHz (40M), 5.7MHz (30M) and 9.6MHz
(20M) LO's for my 4.43 MHz IF receiver. This actually worked out
pretty well for each individual band, but I ended up with lots of
little modules (Xtal osc and bandpass or lowpass filters) for each
band. Since my VFO's tuning range was so small (I only want to cover
the CW section of each band) bandpasses were very practical, and in
fact preferred to get rid of some birdies that I could clearly hear
with lowpasses at the hetrodyne output but couldn't see on my scope.
The gotcha for putting this all in a single chassis was switching
multiple modules for every band.
But then... I saw the G3ROO/GM4ZNX summing-loop PLL in the ARRL
handbook. Hey, that looked pretty nifty. It had diode-switching for
both VCO's and Xtal oscillators, most of all. Had all the parts for at
least a single band in the junkbox... not using those Toko coil forms
in the VCO, but winding toroids and tweaking with NPO ceramics. Didn't
need very many inductors/filters at all. I did use a bandpass instead
of a low-pass at the output of the NE602 mixer. Made a version for my
20M frequencies and was very very happy; no obvious birdies at all in
what I threw together on the bench.
The ARRL handbook notes the CD4046 is not acceptable, but the HC4046
or HCT4046 is. Not really sure of the difference, but all of mine were
HC4046's. Is the actual issue there, something to do with dead-band
issues in the CD4046's phase/freq detector? I understand the 74HCT9046
has an even better phase/freq detector completely eliminating the dead-
zone issue, anyone care to offer any comments?
So I was sketching out how to lay this out for 3, 4, 5, 6 bands and my
receiver chassis, then sat down and went to order some parts. It seems
that my favorite varactor, the MV209, is not stocked anywhere anymore.
a little surprising seeing as how I bought a bunch of MV209's just a
few months ago and everybody had them. But not that surprising seeing
how the real-world is switching to SMT. There are plenty of SMT
varactors out there. And still a couple of through-hole ones somehow
still lingering (e.g. MV2109G, MV2105G at Mouser). I'll try laying it
out for SMT varactors just for fun.
2198 2008-10-06 13:22:14 wimmie262000 Re: Evolving my multiband LO chain, G3ROO/GM4ZNX PLL, HC4046 vs HCT9