[RTTY] Locating the sweet spot

[Kok Chen]

On Apr 17, 2011, at 1:23 PM, Villy Madsen wrote:

> I use a TS-850sat connected for FSK.  I have the mark offset on the TS-850 set
> to 1275 hz & have the sweet spot set to 1360hz that being half way between the
> mark and space signals.  I find that 1275 is easier on my ears than 2125 hz.
> Setting the "sweet spot" to 1360hz gives me a freq readout of halfway between
> mark and space - I don't know if that is valid but it works fine for me...

Using low tones is perfectly valid for FSK, IMHO.

If you are using AFSK though, be sure to check the harmonic distortion of the transmitter.  One reason the 2125/2295 Hz tone pair was chosen during the good old days is so that their harmonics will fall outside the SSB transmit filter's passband.  Most modern transmitters will do fine, especially if you don't have a contester who is close to your QTH.

If you don't like listening to 2.2 kHz audio, you can use the trick of applying an XIT to the transmitter and still using the 2125/2295 Hz tone pair during transmission, while keeping low tones for reception.  The software that you use would need to know how to do that.

Also, with programs like cocoaModem, you can listen to the "aural monitor" from the computer's speakers instead of listening to the audio from the rig's speakers.  cocoaModem allows you to shift the audible tone to what is more pleasing to your ears, while the actual received/transmitted tone pairs is actually something else; see here:

http://homepage.mac.com/chen/w7ay/cocoaModem/UsersManual/Monitor/index.html#rtty

(One of the reasons it was created is because the audible pitch of a PSK31 or RTTY signal can fall anywhere in a waterfall.  Also, when you use two receivers, the "aural monitor" allows to to pick different tones for each receiver to reduce confusion, etc.)

73
Chen, W7AY