[HBR] That General Coverage HBR Project -- 2

[Walt Hutchens]

Bill said:
> 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.

Ah, yes -- that all makes sense.  I just hadn't heard the term.  I 
decided not to go down that path because it seemed to me that the
switching and tuning would get very complicated very quickly.
> 
> I am playing with a spread sheet to look for combinations that might
>  avoid landmines like large birdies, etc.

It could be that I just didn't 'work smart' enough. Hopefully you'll 
come up with something better.

I did feel when I was doing the spreadsheet thing that each additional
mixing created a whole new minefield and that (since I had all the
crystals) there was much to recommend brute force -- the use of just two
crystal frequencies in the front end.

> It just happens that I have a coffee can full of those 25kHz spaced 
> crystals....and several old 23 channel crystalplexed CB radios.

Let me know if you come up missing a few -- I have enough to fill
several coffee cans and could certainly spare a handful or two for just
postage.  No spare 7025's -- the CW boys seem to have eaten all of those
-- but plenty of most others.

These crystals were used (in the BC-1335) in a triode connected 3Q4 
(power pentode) Pierce circuit with the 90 volt plate voltage 
shamelessly applied to the crystal so they are very easy to adapt to ham 
use.

Another idea that might be tossed into the mix would be the use of a 
VXO.  Working on (struggling with ...) the GC-HBR BFO, I did quite a bit 
of reading on the topic and there's more to it than I thought.  The QRP 
boys have come up with several ideas I had never seen.  Of course they 
are all solid state so they require translation.

> 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.

It would be great to hear about more projects here.  I'm still 
recovering from reading about the W6BD receiver.  Wonder where that one 
went?  Boy, what a find THAT would be.

Walt
KJ4KV