[RTTY] Locating the Correct or Best Tx Sweet Spot?

[Dick]

This posting is a revision to my posting on the linux-fldigi reflector that may 
be of interest to some rtty-contesting operators. I am aware many contesters 
prefer and use FSK, but some of us use AFSK.  

The topic is about an experiment in determining the correct or best transmit
Sweet Spot location on the waterfall display in fldigi. The setting is under 
menu item Configure/Misc/Sweet Spot. For those not familiar with W1HKJ's 
fldigi Dave included a really cool QSY button that moves or centers the station 
the operator may want to work to the defined Sweet Spot location on waterfall 
and adjusts the rig's VFO accordingly. This Sweet Spot applies to both Rx and Tx. 

It is my understanding that many operators use 1500 Hz for the Sweet Spot 
to center the rig's Rx filters to the middle of the waterfall display.  When I
received the Kenwood TS-590S, I used 1500 Hz for the Sweet Spot and that 
setting worked fine for receiving and decoding. For AFSK RTTY transmit we 
try to replicate the sound of a FSK signal and I noticed by using the TX Monitor 
that my transmitted signal sounded good but not what I expected.

Having the rig's Sweet Spot centered in middle of the fldigi waterfall is nice
but it is not necessary. As an experiment I have changed the sweet spot from 
1500 Hz to 1000 Hz and adjusted the TS-590's bandwidth accordingly so the 
narrow IF filter bandwidth is correctly located (offset to the left of center) on 
spectral display. With this adjustment, my transmitted RTTY signal sounds 
(to my original issue ears) more like a true FSK signal.

I think many of us tend to worry more about receiving and decoding than 
we do about what we are transmitting.  As you listen to digital signals on the 
bands some really sound strange. I am not talking about being over 
modulation or too much ALC. Some are high pitched, do not sound right 
and are probably off frequency. Some sound card generated PSK31 and CW 
signals sound really sad.

I have changed my sweet spot settings from 1500 to 1000Hz and it seems 
to be working better. The optimum setting for the TS-590S may be closer to 
1100 Hz but I like using 1000 for easier correlation of the rig's dial frequency
to the QSO frequency. 

I do not want to startup another FSK vs. AFSK discussion. This is an AFSK topic 
that may be for interest to other AFSK users. I am still learning the best way to
use TS-590's IF filter. Being able to adjust the bandwidth is just one of the new 
(to me) additions from Kenwood. 

Thanks for reading. I hope it was useful and not too boring.

73 Dick AA5VU