[NJARC] Car Radios

[Al Klase]

Well, I'll do a little speculating here.

The lower you make the IF the easier it is to obtain narrow bandwidth, 
but a higher IF improves image rejection.  Before the short-wave craze, 
IF's on home radios had settled in around 185 KC.  There was a rule of 
thumb in the 1930's was that the IF should be approximately one-half the 
lowest frequency you were going to tune.  Aircraft Radio Corporation 
carried this to the extreme with the ARC-5 receivers.   the 190-555 KC 
set had  an 85 KC IF, while the 6-9.1 MC set had a  2.83 MC IF, etc.

Once you want to build a multi-band radio that tunes significantly above 
the broadcast band, you want to snuggle up toward 500 KC to minimize 
images, 450-480 is most practical.  This higher IF is also a good deal 
for a BCB set that doesn't have a tuned RF stage to fight images.

Now the automobile is a tougher environment for a radio than the top of 
a refrigerator, so the trade-offs are different. Car radios 
traditionally have an RF stage to get better sensitivity, and they don't 
bother with short-wave, and narrower IF bandwidth helps them copy weaker 
signals acceptably, so 262 KC, approximately 1/2 of 530 remained a good 
choice.

I could go on-and-on about why 455 instead of 450, etc., but what I'd 
really like to see is solid information on the radio industry's choice 
of 455 and 262 as standards.

It's getting late,
Al

NICHOLAS SENKER wrote:
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> I am working on an AM  Motorola car radio (transistor) from  1971 which has permeability tuning, typical of that era and an IF frequency of 262 Khz.  I am curious about why the more conventional 455 KHz IF frequency isn't used.  Any comments?
> Nick Senker
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-- 
Al Klase - N3FRQ
Jersey City, NJ
http://www.skywaves.ar88.net/