[WriteLog] bandwith for rtty

[Marty Tippin]

The mostly likely problem for those of you using one of the SSB modes to 
receive RTTY signals is that the passband isn't centered correctly for 
tuning a RTTY signal when you have a narrow filter engaged. The normal 
center of the passband in SSB is somewhere around 1200Hz - with a 500Hz 
filter, you're only hearing the 950 to 1450Hz segment. But the RTTY signal 
is centered near 2125Hz, so you won't print it.

Adjust the IF shift until the signals are strong and printable and you'll 
be in business.

Alternatively, you can use "low tones" and receive RTTY signals in the SSB 
passband. It's not recommende for a few reasons, mainly because of the 
opportunity for harmonics when you transmit. With the normal "high" RTTY 
tones, the second harmonic is well out of the passband of the filters so 
it's suppressed naturally; on low tones, the second harmonic is at the 
upper end of the SSB passband.

Many of us routinely use 250Hz filters with no issues at all, so it's not a 
matter of bandwidth, but a matter of bandpass instead.

-Marty NW0L
  martyt@pobox.com

At 08:14 AM 1/13/2002 , Alan Curson wrote:
>Jay same setup here more or less.  I experience the same issues with trying
>to isolate the weaker signals using the .5 filter.  I have just suspected
>that they are too narrow to tune effectively with just MMTTY software.
>
>John the AF Out is a jack on the back of the rig.  It is a "low level
>receiver output for recording or external amplification."  (From the manual)
>The peak level is 100mVrms at 600 ohms.  It is not affected by the AF
>control on the front panel but is affected by the digital fil controls on
>the front.
>
>
>
> > > I have four filters on the radio. I found that I could copy consistently
> > > using the widest (2.4K) filter, generally OK using the 2.0K filter, and
> > not
> > > at all with the narrower (.5 and .25) filters. This meant that I could
>not
> > > isolate any of the weaker signals.
> >
> > Does the FT-990 allow the use of narrow filters in LSB mode?  If not,
>that's
> > it.  Funny, the 1000MP did allow that, but the newer MARK-V 1000MP does
>not.
> > If this is the problem, use the PACKET jack - That one should've been
> > labeled AFSK instead of PACKET!  Then press the PKT button on the from and
> > you'll be set to use the narrow filters.
> >
> > You mention "AF out", but you don't say where you're getting it from.
> >
> >
> >
> > _______________________________________________
> > WriteLog mailing list
> > WriteLog@contesting.com
> > http://lists.contesting.com/mailman/listinfo/writelog
>
>
>_______________________________________________
>WriteLog mailing list
>WriteLog@contesting.com
>http://lists.contesting.com/mailman/listinfo/writelog