[RTTY] Re More on trying to understand AFSK

[Dick Kriss]

I was pleased to see this topic that has been a long standing
area of confusion for AFSK RTTY operators.  Like Chen has
said many times it works just as well in USB or LSB as long
as you know the correct offset.

As a mater of personal preference I operate AFSK RTTY in
LSB mode and I know the correct offset or Mark frequency.
This is what I use for logging or to spot a a call on the cluster.

If you want to double check your setup, tune in the W1AW
RTTY bulletin. The W1AW signal is transmitted in AFSK with
its Mark to be heard on 14.095.00 MHz by someone with a
semi-modern rig in FSK mode.  If you are operating in FSK
mode, you should copy W1AW on or about 14.095.00. If
you are operating AFSK in LSB mode your frequency display
will read higher unless your rig has an AFSK (not FSK) offset.

For example, I use Chen's cocoaModem with a 2000 Hz
Tone and 170 Hz Shift (2000 ­ 2170) and my Kenwood
display in LSB will read 14.097.00 for the W1AW bulletin.
The only reason I use the 2000 Hz tone vs. the semi-US
standard of 2125 is my brain has less trouble subtracting
2125 Hz from the rig's digital display.

After a QSO, I look at the Kenwood display and mentally
subtract 2000 Hz. For example if the rig display shows
14.087.45, I would spot the QSO as 14085.5 (note most
clusters only use one decimal point).

Some of the cluster spotting errors mentioned may be
due to some users accepting the software logged frequency
as reported by a direct connection to the rig that reports
the USB or LSB suppressed carrier frequency. To test that
your logging software is correctly calibrated with the rig,
try the W1AW test.  W1AW may be off a little and your rig
may not be a perfect as you would like. The W1AW's Mark
will be pretty close to 14.095.

The important thing for AFSK RTTY is to know your Mark
frequency. I hope this helps rather than confuses the issue.
W7AY has a FB discussion of this topic in his cocoaModem
Users Manual at

<http://homepage.mac.com/chen/w7ay/cocoaModem/UsersManual/RTTYPage/BasicRTTY
/BasicRTTY.html>

I am glad to be out of the WAS business with TPA #122 and
hope to work some of you in the the EX RTTY contest this
weekend.  

73 Dick AA5VU