[Boatanchors] Question About Receiver Design - Crystal Controlled Converters

Fri Aug 12 09:59:17 EDT 2022

Al C, Dale, Al K, Bill, Jim, Richard, Many thanks for your answers.

I’m convinced now that single conversion is not the way to go, as I want stability up on 30, 20, 15, etc..  Between reading up on image rejection and the coaching from here, I realize the advantages of double conversion, and even more so, the advantages of the Goodman HB-67 configuration with the converter front end.  Reminds me of a Q5’er sort of….

I am good with the advantages of double conversion for image rejection.  Good.  I’d hate to go off and design up a radio that will be inherently unstable on the higher bands.

The crystal converter logic now makes sense.  With the converters, the 1st IF is created by using a stable crystal oscillator.  In the case of the traditional double conversion like Hammarlund and Hallicrafters, that mixer relies on an LC local oscillator, so I would expect stability and drift issues as it goes higher in frequency.   I will say though that my HBR13 is stable enough on 20 meters.  Don’t know about 15, 12,10.. I’m not taking the chance.

Dales Progressive Receiver is amazing.  The construction is outstanding.  It must have taken a lot of time to design the custom boards, and put it all together!  I have the Progressive Receiver on my radar for a solid state receiver project down the road.

I am concerned about crystal availability though.  I’m more concerned about availability rather than cost.   I see the 10.5 MHz (20m) is a Drake frequency so there is some availability.  I don’t see any for the 11.1 (7 MHz) or others.  Sitting in the back of my mind is the thought of an Arduino with Si5150 frequency synthesizer, but I’d rather not.

Yes I like the idea of optimizing the converter components for each band as necessary.  I also would like NOT having to use plug in coils, so the front end converter gang wiring looks to be a bit easier.  

Someone mentioned to me that they have built many versions of receivers using this converter front end technique, and they build the converter in a separate box than the 80 Meter receiver portion, solely for experimentation.  I hadn’t thought of this before but it is intriguing.  I could easily envision a small cabinet sitting just to the right or left of the 80 meter receiver, an octal power connection, a shielded RCA cable for passing the IF.  Yes it would complicate the mechanicals by having to build 2 chassis or boxes, but it might simplify the over all build by not cramming so much onto one chassis.

I like the calibration comments.  You’re right, calibration would be a breeze, and not dependent on frequency. 

On the comment about up conversion and down conversion, I am familiar with that and have used both, once accidentally.  For my Mate receiver, the handwound coils ended up having to much inductance, so the LO frequency was significantly lower.  I was planning on high side injection.   It was actually in the right spot for low side injection, so instead of removing turns on the coil, I just left it feeding the mixer from the low side.  That was my introduction to high/low side injection.. hi hi  

I really appreciate the chance to run these issues past you guys.  I am a beginner builder with two receivers under my belt, learning a ton, and with a lot more to learn.  Your input is greatly appreciated.  Thanks. 73 Scott WA9WFA

From: Allan Culbert <radio.k0al at gmail.com> 
Sent: Thursday, August 11, 2022 8:16 AM
To: Whitebear1122 <whitebear1122 at comcast.net>
Subject: Re: [Boatanchors] Question About Receiver Design - Crystal Controlled Converters

Hi Scott,

Images are not as much of a problem on 80 and it saves one crystal and associated circuits. This was used on some commercial receivers, HRO-60 was that way.

I am away from home, but when I return I will look to see if I have the coil stock you were looking for - unless you found a source.

73,

Al, K0AL

On Thu, Aug 11, 2022 at 9:09 AM <whitebear1122 at comcast.net <mailto:whitebear1122 at comcast.net> > wrote:

I'm looking at Byron Goodman's HB67 receiver in the ARRL Handbook 1965.  His
design uses crystal controlled converters for 40-10 ahead of an 80 meter
receiver.  I see this is single conversion on 80 meters as it bypasses the
converters, then double conversion on 40-10.

What are the advantages and disadvantages of this configuration over the
other receiver designs where the local oscillator is changed to mix 80-10?  

Thanks. 73 Scott WA9WFA

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