[GreenKeys] Auitostart Net - Shift

[Bob Camp]

Hi,

I don't have a particular problem with any shift. The only thing is 
that it's always a trade off between interfering signals (narrow = 
good) and fading (wide = good). At 45 baud you don't get much advantage 
in bandwidth increase as you go to wider shifts.

If we go with crystal filters on the input to the receiver there are a 
few issues. To do a true 200 hz wide input filter then you need 
something around 2 to 5 ppm stability crystals. To do a wider shift the 
stability requirement isn't quite as tight. Once you look at Q and 
insertion loss I suspect we would be running around 500 Hz just to keep 
things reasonable.

Gotta stop trying to work all these complex questions on Cinco De Mayo. 
Tequila and RITTY don't mix well ...

	Take Care!

		Bob Camp
		KB8TQ



On May 4, 2004, at 10:48 PM, Roy Norris wrote:

> Hi,
>
> Bill Henry made a very important observation early in this discussion 
> on
> the autostart net  concerning shift.  Amateurs moved to `170 Hz shift 
> as
> standard practice back in the  late 1970's.  In doing so, we lost an
> important weak signal advantage which is that for shifts of 425 or 850
> hz, the respective mark and space signals will not fade in unison.  
> This
> allows copying weak signals on either the mark or space channel alone
> during deep fades of the opposite channel if you are operating in the 
> AM
> mode.  Both the Dovetrons and the Hal units can do this and it will
> result in significantly improved copy under weak signal conditions if
> your TU will support that mode.
>
> The down side is that we would take up more spectrum space with the
> wider shift.  As most TU's will accommodate either 170, 425, or 850 hz
> shift, it might make sense to use one of the wider shifts.
>
> What say the group ??
>
> Best regards - Roy, K4EEG
>
>
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