[HBR] My approach to the HBR... Suggestions?

[Peter Bertini]

On Sat, Sep 13, 2008 at 10:53 AM,  <Hopperdhh at aol.com> wrote:
> Pete,
>
> I have never liked audio derived AGC.  As you tune  through zero beat on CW
> the gain goes up and down.  Pumping problems are  hard to control.  You will
> not be able to achieve the kind of attack times  you can with IF derived AGC.
> You may need a separate IF amp for the AGC to  help keep out the BFO signal.
> At any rate take special care to isolate the  BFO.  I built an SSB transceiver
> once that had excellent AGC  characteristics after studying the time constants
> (different for RF vs. IF) used  in the Drake TR4.

I'll have to look at the Drake schematics, no sense reinventing the wheel!
>
> Keep in mind that the 85 Kc ARC-5 IF cans are  relatively low Q -- about 60
> if I recall.  Bob Drake was my hero when it  came to filter design.  The Drake
> 2-B has only 4 tuned circuits at 50 Kc,  but the Q must be pretty high.  There
> are cores available today to take  that approach, but the ARC-5 coils will
> work.  Since you have them, and  have space for them, give 'em a try.
>
> I like your idea of using more tuned  circuits and sweep tuning them.  You
> might also try LTSpice (free download  from www.linear.com) to model the filter.
>  Its easy to try different  coupling circuits and values once you have
> measured the L and Q of one of the  coils.  I would assume 1 megohm for the input
> and output tube  loads.

Thanks!  I'll check the link.  How do I model the coupling between the
coils in the
IF?

>
> You will probably need to remove turns from the 1415 Kc cans to  move them up
> to 1600.  You may not need 4 cans at 1600, I would breadboard  up a one (or
> two) tube test circuit to see what kind of response two cans have  at two times
> 85 Kc away from the peak.  (LTSpice could be used here  too!)  Also, using
> 1605, or 1655, etc., may be a better choice to reduce  interference from BC
> stations.

One of the notes on the HBR site mentions that replacing the silver mica buttons
in the 1415kc IFTs with fixed 120pF SM caps will raise the frequency to 1600kc.
I have two hetrodyne xtals, so I can move the first IF a few kc if the
local 1600
station is a problem.

Pete

>
> Best of luck -- have fun,
>
> Dan K9WEK
>
>
>
>
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