[HBR] HRS's?

[Dan Merz]

Steve,  the hbr numbers are explained in a table showing all the models on
the HBR page.  About i.f. frequency,....  generally a higher i.f. for the
first conversion will reject images better (those signals that are twice the
i.f. frequency away from the desired signal)  1600 khz or higher is adequate
without putting in an extra rf stage;  before dual conversion sets became
more common, 455 khz was common and to get really good image rejection, an
extra stage of rf tuning was used in the best sets.  Why would you want low
freq. i.f..... Because the selectivity improves/stage with lower i.f.
frequencies when tuned i.f. transformers are used (cheap way to go).  This
is why 100 khz i.f.'s are used for the second i.f. in HBR's,  namely to
improve the selectivity without having to resort to expensive items like
crystal or mechanical filters and with a reasonable number of stages.  The
use of tuned i.f. transformers in the HBR design drives the wagon.. .  Low
second i.f. frequency to get selectivity and sufficiently high 1st i.f.
frequency to  attain image rejection.  Best regards,  Dan.       

-----Original Message-----
From: hbr-bounces at mailman.qth.net [mailto:hbr-bounces at mailman.qth.net] On
Behalf Of StephenTetorka at cs.com
Sent: Tuesday, January 10, 2006 7:11 AM
To: hbr at mailman.qth.net
Subject: [HBR] HRS's?

Hi all:

As I'm very new...might someone explain the differences with the various HBR
numbers.

Here's a 'big' question...how & why is "IF" choice important?

Regards,
Rookie Steve
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