[GreenKeys] Odd FSK values...

[Ralph Mowery]

Filters that can be tuned is what is needed.  However the TV coils while they can be tuned to work on 170 Hz shift are getting to the point where they are not sharp enough to work very well.  I had a TU years ago that used the TV coils.  It would work on the narrow shift when tuned,but were not sharp enough to work well.

 

The Flesher tu 170 probably can be tuned to work.  I am thinking that the filters need  to be retuned so the tones match the shift  or it will not work as it needs both tones to copy.

 

I have not tried it, but in the original write up Hoff indicates that the ST-6 can copy  signals that are only shifted a small amount by straddle  tuning.  That is  do not tune the mark signal in as 2125 Hz,but somewhat closer to the center say maybe 2180 to 2190 Hz if set for 10 Hz shift.   

 

One other thing that could be tried for the ST-6 is if your receiver has a sharp enough filter is to filter out the space tone and copy on mark only.  Some receivers have a notch filter that may be sharp enough to eliminate the space tone.

 

 

 

From: greenkeys-bounces at mailman.qth.net [mailto:greenkeys-bounces at mailman.qth.net] On Behalf Of Kenneth Gartland
Sent: Thursday, August 03, 2017 10:50 PM
To: greenkeys
Subject: [GreenKeys] Odd FSK values...

 

Hi all!

 

Tks Jim for the excellent description of this 

frequency shift & overview of the TU operation...

 

I think he (Jim), is correct in saying "Tuneable" filters such

as those found in the W2PAT TU design, using the TV 

horizontal width coils, mite work for those odd value

shifts like those with DDK WX transmissions...

 

Probably not many RTTY enthusiasts are using

TU's like these early designs anymore, so I am

thinking the Dovetron TU and perhaps the modfied

CV89's can decode these odd shift values...

 

Perhaps someone on the list cud try the WX svc

with the 85hz shift to see if they can take copy...

 

Back to Jim's mention of the "Tunable" filters...

 

I was looking at those TV width coils in the W2PAT

TU, and they have a very large amount of adjustment

range, and with additional capacitance padding,

mite work on these very narrow shifts...

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