[HBR] The long, SLOW HBR project

[Walt Hutchens]

Bill Cromwell said:

> Your running dialog is motivating me to build a 'modified' HBR, too. I
> think you added a crystal filter at your first I.F. and I plan to do
> that, too. I am planning to stay closer to the original design first
> I.F. and build the filter at that frequency ala HR10 (one of which I
> have). I also have 3.395 and 9 mc filters available. For the second I.F.
> I'm using the 85 kc cans and BFO coil from an R-23. The RF selectivity
> will only be an SSB bandwidth and so something like a selectoject or
> other audio filter will have to help out for anything narrower.

Sounds like a plan.  But ... why not just go with the 1.681 (or whatever it
is) IF of the HR 10?   The crystal filter immediately follows the mixer
circuit which is where you  want most of the selectivity and with two good
IF stages at that frequency, you're in business.

You could do a lot worse than following the plan of the HR 20 from there on
-- basically HR 10 + product detector.  Or go with the HBR setup but don't
bother doing a second conversion.   The sets are actually a lot alike except
for the bandswitching and cheaper construction of the Heath sets.

I would definitely use the circuitry of the HBR sets (but without the 2nd
conversion); the Heath design is tuned for maximum cheapness.   Read the
reviews of that set ... it was dead on 15-10M and there was no AGC for SSB
and CW.   I'd bet on poor AGC, BFO pulling, an unstable LO ... the HBR
designs will run rings around it.

The purpose of the second conversion in the HBR sets is to make selectivity
easy and (with the parts of 1960) relatively cheap.   But you've got a
perfectly good crystal filter; you don't NEED to convert to 85 kcs.

The far-out selectivity with a half lattice filter (as in the HR 10 and my
current project receiver) isn't terrific, but it seems to be good enough.
Adding an 85 kcs IF behind that would make it great but that's pretty much
work for a problem I haven't noticed  yet.

There's an added bit of fussiness if you have high selectivity at two
different frequencies: The conversion between them has to be perfect.
Meaning that the 2nd LO has to be spot on frequency and no drift.   It's
doable but it's a nuisance.

The HR 10 has just about all the electrical parts you need.   That's an
interesting way to tackle an HBR project ...

Walt Hutchens
KJ4KV