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
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