[HBR] HBR progress - crystal question

[Bill Cromwell]

On Mon, 2012-04-02 at 17:08 -0500, Chris Howard w0ep wrote:
> I was working on an old Hallicrafters SX-11.  It has a crystal
> in the IF chain, between two transformers.
> 
> And, I happen to have a an old Valpey crystal module
> thingy, about the size of a golf ball, that says 81.962 on it.
> (It's chromed too.)
> 
> So I have some vague idea that, if I ever get my HBR
> working, maybe I should then go back and see if I
> can incorporate this crystal as a CW filter in the IF stage.
> 
> I'm mentioning the idea now because it may have a bearing
> on my mixing scheme if I want to use that.  My IF transformers
> are from the command set, 85 kHz.
> 
> Here's your opportunity to tell me this is/is not a good
> line of thought.
> 
> Chris
> w0ep

Hi Chris,

I have only used the 85 kc I.F. cans at 85 kc and in fact in the R-23
and BC-453 receivers. I don't know if those will tune down to ~81.962 kc
but it seems reasonable. It shouldn't change your mixing scheme so very
much, either. It should be just a realignment. If your last conversion
is xtal controlled the crystal will have to be changed. If it's an LC
oscillator just dial up the new frequency and GO. Retune the BFO, too.

You probably won't need to go to the trouble of adding that xtal to your
I.F. Those I.F. cans will give you a narrow I.F. channel and "single
signal" reception should be pretty much assured. For the narrowest CW
filtering you will get good results from an audio filter immediately
following the detector at the low level end of your audio chain.
Concerns about your narrow filters not protecting your front end from
out of bandwidth signals and the AGC issues already do not apply to this
design. The knothole is already NOT up front.

I have used the R-23 to prop up a weaker receiver with 455 kc I.F. and
the results have been excellent using the audio filter as described. It
should do well in your HBR without the xtal. I have some of those cans
now, too and I'm getting started. I have been tempted to turn my HR-10
into an HBR project like Walt's and maybe I will yet. First, I want to
build one that is closer the original designs. Mine will be a "two
piece" with separate power supply and audio output as described in
another post.

73,

Bill  KU8H