[RTTY] FSK and ft-1000mp

[Kok Chen]

On Mar 10, 2005, at 2:09 PM, KO1H wrote:

> Hi all, I have one question (after I worked out a bunch of problems 
> myself). I have gotten fsk working on my ft1000mp but I need to know 
> if I should have the Menu setting for Offset or Carrier. in the menu 
> settings?

You probably want "Offset" and not "Carrier," IMHO

"Carrier" would display the suppressed carrier frequency of the SSB 
receiver onto your VFO dial, which is pretty meaningless for figuring 
out where your RTTY signal is landing on unless you also know the tone 
pair that you are using.

If you have selected the 2125/2295 tone pair for example, selecting 
"Carrier" would display a frequency on the FT-1000MP dial that is 2.125 
kHz up from your mark carrier and 2.295 kHz up from your space carrier.

If you select "Offset," the FT-1000MP will display the frequency that 
your Mark tone lands on the RF spectrum, and is also the standard way 
RTTY "operating frequency" is defined as.

Having a direct readout of your mark on the RF spectrum makes it much 
easier to figure if you are "out of band" or transmitting on top of the 
DX beacons without having to mentally do some subtractions.

The majority of the folks also spot the mark frequency to the 
PacketCluster, so that is yet another reason to use "Offset."

>  I've worked everything else out I just need to know which of these 
> is the standard aka what will put my tones in the correct band pass 
> of the other stations receive when I have their tones printing at 
> mine.

Don't worry about the correct passband versus the tones; the FT-1000MP 
will perfectly center the IF passband to the tone pair that you have 
selected in the FSK menu, even if you'd choosen 250 Hz filters.  The 
choice of the tone pair to use is therefore an individual choice.  Some 
people prefer one of the lower tone pairs because it is kinder to the 
ears.

If you are using AFSK, then there is a reason to use the higher tone 
pair.  Using the 2125/2295 tone pair throws any harmonics up to 
frequencies beyond the SSB transmitter's bandpass filter and that helps 
provide some protection against overdriving.  Since you are using FSK 
on the FT-1000MP, where the digital synthesizer of the rig is doing the 
actual frequency shifting, this is not an issue.

73
Chen, W7AY