[RTTY] Off Frequency Stations.

[Bill, W6WRT]

ORIGINAL MESSAGE:

On Thu, 23 Sep 2010 06:55:07 +0000 (GMT), Mick Mc Grory
<mi0grg at ymail.com> wrote:

>
>When taking part in the BARTG 75 Sprint last weekend,a lot of Stations who 
>answered my CQ call were slightly off my Frequency,so I had to fine tune their 
>signal with my RIT control.

REPLY:

Hi Mick, welcome to RTTY.

  It could be you or it could be them. The culprit is usually incorrect
use of AFC. The problem happens when AFC causes your (or his) TX and RX
frequencies to be different. When running FSK, as you are, AFC only
changes your RX frequency. Your TX frequency is set by the transceiver's
VFO and AFC has no effect on it. 

There are two ways this frequency mismatch can happen. 

if you run MMTTY with AFC on and you are S&Ping, what happens is you
will be tuning across the band and when you come near a station, the AFC
will reach out and capture the station and tune it in correctly
according to the tuning indicator. The problem is that as soon as AFC
captures the station, you naturally stop turning the VFO and as a
result, your TX frequency is slightly off the RX frequency. This is
usually the cause when you are answering a CQ and you think you are
right on his frequency but actually you are not. 

The other way the mismatch can happen is if you turn AFC off while the
mismatch exists. You can correct the mismatch by always clicking the HAM
button after turning off AFC. If you look at the MARK frequency in
MMTTY's main window, it should be 2125 whenever AFC is off. Clicking the
HAM button sets it to 2125 if it is off. 

I realize this is a little bit arcane, so here are some simple rules you
can follow to make things work right:

1 When you are CQing, have AFC on and do not touch your VFO knob. Let
AFC do all the tuning-in.  Generally, MMTTY has enough range on the AFC
that you should not have to use your RIT unless the calling staion is
really way off. 

2. When S&Ping, turn AFC off, click the HAM button at the start of the
S&P session and verify that the MARK window says 2125. Doing this will
assure that your TX and RX frequencies are exactly the same and will
stay that way until you turn AFC on again when you go to CQ mode. 

If you are running MMTTY standalone, you will have to do the above
button-clicking manually, but if you are running N1MM Logger and using
the MMTTY engine, there are two check boxes in the digital interface
Setup>Settings window that will do both 1 and 2 for you automatically.
The two boxes are the ones where the text next to the box starts with
MMTTY in parentheses. Check both boxes. 

I realize this is a little confusing at first, but once you get it
right, it never changes. If you have any questions, feel free to ask. 

Incidentally, the NET button has no effect while running FSK. It can be
either on or off, doesn't matter. I leave it off. 

Hope to work you in the CQWW this weekend. 

Bill, W6WRT