[HBR] Looking for some parts, leads welcome..

[Walt Hutchens]

> I'm also looking for a source of crystals in the 1600kc region, need
> pairs with a 1.5 or 2 kc separation to make a half-lattice filter
> for the front end.

Because the 1st IF, 2nd LO, and 2nd IF must be consistent, this is a
difficult situation.  There are two practical approaches:

1. Find a set that has roughly what you want, that you can scrap for
the filter crystals and the LO crystal.  You MIGHT be able to roll
your own 2nd IFs -- say, adjust 85 kcs IFTs to 100 kcs or vice-versa,
but the best approach is to get all three from the same set.

Or,

2. Get your 2nd IFTs at whatever frequency you can find and then
special order either or both of the filter crystals and the 2nd LO
crystal.

A possible variation: Scrounge a 2nd LO crystal and purchase filter
crystals (and tweak the 1st IF) to match.

There simply isn't a good supply of crystals in the 1700 kcs range so
that you'll be able to find a pair with proper spacing.  The most
direct approach is probably to find a 2nd LO crystal and buy the
matching filter crystals.

Filter crystal pairs MUST be same manufacturer, same time, or they
will not pair properly.  It's not just the frequency that matters but
also the Q and spacing between the series and parallel resonant
frequencies.  Even many of the WW-II crystal types -- the popular
FT-243 holders, for example, were made to many different specs --
CR-6, CR-8, and more -- and the specs themselves were not particularly
tight.

Furthermore, pairing pressure mount crystals (the FT-243s) is not
great fun at the very best, because of the variations in Q.  You
really want plated/wire mount for this job.

Custom crystals run around $25-30 each and you can expect to wait a
month to get them. The cheaper and probably faster route is to find a
junker set that has what you need -- and that set will have much other
useful stuff. I've built two receivers based on the FT-101 chassis and
will probably do it again.

I've done 3-4 half lattice receivers; all used custom crystals.

You could consider ditching the half lattice to start.  Build the set
with a conventional 1st and 2nd IF, per the W6TC designs -- that is, high-Q 
coils for the 1st IF.  He
confronted exactly the issues you are facing and decided that most
hams would be happier that way.  HIS DESIGNS WORK JUST FINE.

Four 85 kcs IFTs from R-23/ARC-5 in two pairs (single 2nd IF stage) gives about the
maximum selectivity that you can use for SSB with all the rods pulled
up; it's a bit tight (but useable) for AM if you tune to one sideband
or the other.  With rods pushed down it'll be fine for AM.  You
cannot, however, move the rods up and down frequently -- the mechanism
isn't designed for that.

Speaking more generally you might want to narrow your approach
to something close to a single recognized design. I DON'T do that -- I
do all kinds of different stuff -- but I've built about 10 receivers
and I am at last up to a 50% success rate. I cannot recommend my
'contact sport' approach (colliding with my own ignorance) to anyone
else.

Only you can decide the balance betweeen new ideas/potential best
performance and risk of being unable to get it to work.

Walt
KJ4KV