[RTTY] Crystal filter width preferences for RTTY contesting

[Bill, W6WRT]

ORIGINAL MESSAGE:

On Tue, 25 Aug 2009 12:23:26 -0500, "Jeff Blaine AC0C"
<keepwalking188 at yahoo.com> wrote:

>
>Q1. If you only were to get 1 filter, what width would it be?
>
>Q2. If you were to want to fill both filter slots, what widths would these 2 filters be?

REPLY:

According to the math experts (I am not one), a 170 Hz shift RTTY signal
actually  occupies about 350 Hz when you include the sidebands. As you probably
know, RTTY is a form of FM and FM generates sidebands. Think of a carrier, FM
modulated by a square wave. That's RTTY.

When QRM will allow I find I get slightly better print on weak signals with a
300 or 350 Hz filter, but during a busy contest that's a bit too wide, generally
speaking. In a contest I use 250 Hz almost exclusively, but when there is a weak
signal and the QRM will allow, I widen it up.

This also depends on the steepness of your filter skirts. A really straight up
and down skirt needs a slightly wider filter or it will attenuate the sidebands
too much. In other words, you will have to experiment based on your particular
receiver. 

But to answer your question: For contesting with only a single filter, 250 Hz.
For DXing or ragchewing with only a single filter, 350 Hz. For all uses when two
filters are available, 250 and 350 Hz.

Hope this helps.

73, Bill W6WRT