[HBR] That General Coverage HBR Project -- 2

[Bill Cromwell]

Walt KJ4KV said, among other things:

"Crystalplexer" is a term I haven't heard but the scheme in the GC-HBR
is to use the tenth harmonic of the 120 crystals of the WW-II surplus
BC-1335 FM set.  They run 5675-8650 kcs I think, by 25 kcs steps so that
gives you 56.75 -86.5 Mcs.  Subtract from that 49.2 Mcs yielding
7.55-37.3 Mcs.  Use that as the crystal mixing frequency to get to a 1st
(tunable) IF of 5.550-5.80 Mcs with coverage of 0.75-30.5 Mcs.  (Front
end probably won't tune the bottom end -- I don't need the BC band and 
the first few crystals show up in the tunable IF so they'll give large 
birdies.)  The 2nd (fixed) IF is 4.096 Mcs (clock crystals are 
available) and LO tunes 1.454-1.704 Mcs.

That's all from memory so if it doesn't quite add up ...

Hi Walt,

....and everybody.

It does add up Walt. I am revisiting the "crystalplexer" as used in 23
channel CB radios before the switch to PLL frequency control. That block
of crystals you describe at 25 kHz times ten gives you 250kHz "steps".
If that block only used four crystals at 25kHz spacing you would get an
output (at 10x) that covers one MHz with 250kHz steps. Then revisit that
49.2 MHz oscillator and add crystals at one MHz steps. The one Mhz steps
could be selected for ham band only use (or CB channel selection). Even
with a "zero to 30 MHz" frequency coverage the number of crystals is
dramatically reduced to something like 34 from 120. Add a vfo with a
250kHz range.... Other combinations are possible.

I am playing with a spread sheet to look for combinations that might
avoid landmines like large birdies, etc. It just happens that I have a
coffee can full of those 25kHz spaced crystals....and several old 23
channel crystalplexed CB radios. I suppose I would be excommunicated if
I used this info to build a solid state radio. So I will use the info to
build a vacuum tube based radio instead.

73,

Bill  KU8H