[Boatanchors] Question About Receiver Design - Crystal Controlled Converters

[Al Klase]

Scott,

Important parameters in any receiver are frequency accuracy, stability, 
and freedom from spurious responses (image rejection).

It's pretty easy to design an 80-meter set with, for example a 455 Khz 
IF, that offers good performance.  However, as we go up in frequency 
everything become more difficult.

Multiple conversion (double in this case) reduces the image rejection 
problem.  The image will be two times the IF frequency away from the 
desired signal.  So 910 KHz in the case of 455 IF, becomes about 8 MHz 
with a nominal 4 MHz first IF.  So the preselection filtering is easier 
to accomplish.

Crystal control of the first oscillator results in essentially the same 
frequency accuracy and stability as you's have on 80 meters, even when 
operating on 10 meters.

Down side is the cost of the crystals, but if you're only worried about 
a couple of bands, it's not too bad.  It's a much bigger problem for 
general-coverage radios.  Take a look at the Collins sets like the 51J 
and R-390.

Hope that helps,
Al


ARK Sig Block Al Klase - N3FRQ
Jersey City, NJ
http://www.skywaves.ar88.net/
On 8/11/2022 9:08 AM, 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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