[CW] IF Intermediate Frequency

[Donald Chester]

>From: Ed Tanton <n4xy@earthlink.net>

>It's a simple matter of the frame of reference, isn't it?
>
>If one is referring to transmitted/received RF, then it is LF. If you're 
>talking about receiving, then "IF" applies. After all, a popular "IF" 
>frequency for radio-astronomy is 70MHz... a far cry from 455kHz!

And some rigs "up-convert" to a higher frequency IF like 70 mHz first IF, 
then down-convert to the filter frequency which may be somewhere like 5 mHz 
or 9 mHz.

Of course there are the "variable IF" or "tuneable If" configurations, which 
use a crystal controlled 1st oscillator, tuneable 1st IF to a 2nd IF at the 
filter frequency.  This gives better stability, since it is easier to build 
a stable VFO  that covers one  fixed  frequency range. 5-5.5 mHz is a 
popular one.  It is very difficult to build a bandswitched high frequency 
oscillator to cover the 20 thru 10m. range.

I don't see how anyone worked CW with older low-cost receivers that drifted 
all over the place.  I remember my 1959 Novice days, staying on 80m because 
my old shortwave BC set (with homebrew add-on BFO) wasn't stable enough to 
work 40 - and some of the cheapie ham rx's of the day were even worse.  The 
only pre-WWII  receiver that I have ever seen that was even half way stable 
enough to use a sharp xtal filter is the old National ones  like  the HRO 
and the Nationals with the sliding coil catacomb assembly.  You had to let 
them warm up 30-45 minutes before they settled down.  The old Hammarlunds 
never would stop drifting, and Hallicrafters were mechanically unstable.

Collins first came out with the idea of the tuneable IF with the 75A series. 
  That was as much a quantum jump in rx technology as the  superhet was over 
the trf and regens.

Don K4KYV

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