[RTTY] High tones v Low Tones

[Richard Ferch]

I am not subscribed to the reflector; I just read the archives at
contesting.com -- so, I don't know whether this will make it to the mailing
list or not. Anyway, here goes...

Phil, I don't think you are daft at all. I happen to use the exact same
choices as you, although for slightly different reasons. When I used to use
FSK on my TS-850S with a MFJ-1278B TNC, of course I used high tones and LSB,
as that was what I had the hardware configured for, but now that I am using
AFSK, I also use low tones and USB.

A digression: I switched from my trusty old 486 to a Pentium computer a
while back, and WF1B no longer works for me. I get Runtime Error 216,
apparently because the program cannot find the COM port. Almost none of the
other DOS software I have seems to be able to find this COM port either
(it's COM1 on the motherboard, BTW, so the problem is probably in the
Windows 98 configuration, not the hardware). The exception is TRLog, which,
even while running in a Windows 98 DOS box, finds the port OK. However,
TRLog's TNC port runs at 4800 baud, and several years ago I set the autobaud
off on the MFJ so it's stuck on 9600, and all TRLog sees is gibberish. I
know how to fix that, but it involves taking the TNC's cover off, and since
I had previously determined to my own satisfaction that MMTTY decodes better
than the MFJ, my incentive to unplug the TNC from the rat's nest of wires
behind it so I can get it working again is a bit weak, especially since the
only software I have that will see it was not designed for RTTY. If anyone
knows the secret to configuring a COM port in Windows 98 so that WF1B can
see it, I would appreciate the information (BTW, I suspect TRLog works
because it polls the port continuously, whereas I suspect most of my other
software, including WF1B, is interrupt-driven, and Windows 98 is not passing
the interrupt through - but I don't know how to fix that; and no, I am not
going to boot the computer to MS-DOS - this computer also acts as our home
network server, and it needs to be running Windows to support the network
software we are using...)

Back to topic. I now use AFSK for RTTY, with either MMTTY or MixW 2.0 (but I
wish my AFSK software was better for contesting - I miss WF1B!). In SSB
mode, the passband of my radio's 500Hz filters passes the low tones, not the
high tones as in FSK. Incidentally, my radio's passbands in LSB and USB are
not quite the same. I don't know whether this is a bug (misalignment) or a
feature, but it means that in LSB I can use the 1445 Hz mark frequency, but
in USB I use 1360 Hz or thereabouts in order to centre the signal in the
passband.

Like you, Phil, I find the low tones much less irritating, and MMTTY seems
to work better with low tones. Using narrow IF filters, as I am, there
shouldn't be any worry about harmonics getting passed through by the TX,
which seems to be the main argument in favour of high tones. I also use USB,
mostly because some of the other digital software and modes I like to play
with are set up for USB.

Phil, in your earlier message you made a comment about not reporting the RF
frequency correctly. One solution: if you use MixW with your radio
interfaced, the frequency on the MixW screen corrects for the audio offset
whether you are using USB or LSB. The only snag is, MixW uses the center
frequency instead of the mark frequency, so it is always 85 Hz below the
frequency that people using FSK will report (which is the mark, or higher
RF, frequency). An error of 85 Hz is probably not worth getting excited
about.

If you are using non-interfaced software such as MMTTY, then in USB you have
to add your higher audio frequency (what MMTTY calls "space", which is equal
to mark + shift - actually, in Reverse it is really the mark frequency, but
that's another argument for another day...) to your radio's indicated
frequency to get the actual RF mark frequency. If you use LSB, you have to
subtract the mark (lower) audio frequency from your radio's indicated
frequency. Since many of us find adding easier than subtracting, that might
be another reason to use USB, with MMTTY in Reverse mode. If you haven't got
your mark and space frequencies straight, there's a possibility of making a
170 Hz error. That's still a lot better than the 1445 Hz error you will make
if you just report the frequency on your radio's dial (using low tones and
USB; the error would be 2125 Hz in the opposite direction with high tones
and LSB).

Hoping that I have got this right, and also that my description hasn't just
increased the confusion...

73,
Rich VE3IAY