[GreenKeys] Might be a bad weekend...

[jhhaynes at earthlink.net]

On Sat, 1 Dec 2007, Ron Ott wrote:

> I believe that 170Hz shift became practical with the advent of op amp filters. On the other hand, you can make adequate filters and discriminators with toroids and tubes.
>
> Ron, W6XY
>
It's not all that hard to make 170 Hz filters with toroids and capacitors.
In fact in commercial service there were carrier systems operated over
telephone lines that used 85 Hz shift way back in the 1940s.

Hams originally adopted 850 Hz because that is what the military and
commercial operators were using, presumably to allow for considerable
frequency inaccuracy and drift.

There was quite a bit of discussion before 170Hz was settled on as the
ham standard for narrow shift.  That is one-fifth of 850.  85 Hz was
mandated as the narrow shift for some MARS operations, but perhaps hams
at the time considered that too narrow because of drift.

There was some use of 425 for non-ham operation in earlier times, I guess
as the commercial/military users tried to get something narrower than 850
and still cope with the drifty equipment they were then using.  For hams
it didn't seem worth it to go from 850 to 425 when operation at still
narrower shifts was known to be feasible.