[RTTY] Best MMTTY profile for noise and weak signals?

[Jeff Blaine]

Guys,

The tuning sensitivity comes down to two factors.

First, the 512 refers to the number of "taps" the program uses in its' digital filtering process.  Just consider a higher number as 
equating to a steeper filter skirt wall.

Secondly, the FW number is what actually sets the DSP filter band width.

By clicking on the SHOW button you can see roughly what the filter's passband will look like.  [Unfortunately, the effect of the 
notch is not shown graphically that I can determine.]

With a 512 value, the skirts are very steep - and so you don't get much visual help if you are close or way off the tuning point. 
But it's a combination of the two.

So try both and see how you like it.  You may find the tuning easier with 256, etc.  For me, I prefer to remain with the 512, and 
then adjust the FW depending on band conditions.  When the band is crowded, a 80 number works well.  For less crowded conditions, 
tuning is easier at 100 or 150 because that makes the waterfall passband wider.

But you have a trade off here from a theoretical standpoint.  The more narrow the filter (and more vertical it's skirts), the lower 
the useable SNR can be.  However, in a contest environment, speed is a factor also.  So at some point, the more narrow filter's 
sensitivity to tune starts to hurt you with respect to tuning speed.  And given MMTTY has no "playback" of prior AF, you only get to 
see the conversation play out once you are tuned.  In addition, there is some amount of power in the sidetones which - with a tight 
filter - will be cut out as well and will degrade the useable SNR.

73, Jeff ACØC
www.ac0c.com

-----Original Message----- 
From: Dick Flanagan
Sent: Friday, January 14, 2011 3:00 PM
To: dezrat1242 at yahoo.com
Cc: rtty at contesting.com
Subject: Re: [RTTY] Best MMTTY profile for noise and weak signals?

At 09:37 AM 1/14/2011, Bill, W6WRT wrote:
>Also, Dave, AA6YQ has released a new profile for MMTTY called AA6YQ
>FIR512 which is supposed to be super good at weak signals. I will try it
>out in the upcoming UK DX contest this weekend. I understand it requires
>more critical tuning than other profiles, so be aware.

When running, can AFC be used to affect this critical tuning?

Dick
--
Dick Flanagan K7VC
dick at k7vc.com
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