Whether you find an interesting signal by clicking on traces in a
panoramic tuning display or by rotating your tranceiver's tuning
dial, ideally you should then direct your digital mode application to
place the selected signal at a pre-specified optimal audio offset by
appropriately QSYing your transceiver.
Though different names are used to describe this function, most
digital mode applications have provided it for a long time.
73,
Dave, AA6YQ
--- In digitalradio@yahoogroups.com, "G. McFarlin" <[EMAIL PROTECTED]> wrote:
>
>
>
> So which is better, park the dial and move the audio
> center frequency (ACF) “marker”, or park the marker and
move
> the frequency dial? The former seems to be the standard method used
for
> PSK31 (when using programs like Digipan and PSK31), but the latter
seems
> to make more sense in the context of finding your peak output point
in the
> bandpass and leave your marker there for best decoding. Is it
partially
> dependant on the available filters and/or the age of the rig and its
> ability to handle digital modes?
>
>
>
>
> This latter concept seems to fly in the face of guidance
> (at least for modes like Olivia) provided on hflink.com and other
tutorial
> sites where the ACF marker is supposed to be set in accordance with
the
> tone pair/mode in use and the frequencies are voluntarily set based
on the
> “sub-band” (.65 or .50, etc). This suggests that both
the
> frequency and ACF should be fixed or channelized, regardless of rig
or
> bandpass “sweet spots”.
>
>
>
>
> From the context of making it easier to find signals and
> establish QSO’s, this guidance makes sense, assuring (to some
> degree) that if your dial is set to a specific frequency and your
ACF
> marker is in the proper spot for the tone pair in use, any one who
comes
> along can find you quickly. If everyone running Olivia between
14104 and
> 14109 used “channels” on .50, a tone pair of 1000/32
and a
> marker on 1000hz (at least to call CQ) QSOs would be much easier to
locate
> and lock onto. Between 14072 and 14078, “channels”
should be
> on .65, running 500/16 with an ACF of 750Hz. Easier, but is it at
the
> expense of best decoding, power output, and QRM avoidance?
>
>
>
>
> Again, this is all by gentlemen’s agreement, but
> there seems to be little other established guidance in print or on
the
> web. Was this originally suggested to assist in happily co-existing
with
> other “channelized” modes frequently found in these sub-
bands,
> like Pactor? Wouldn’t the “park the marker, move the
> dial” method make it difficult to post and follow digital
spots on
> sites like Andy’s (K3UK) if everyone’s dial showed a
different
> frequency? (A minor concern, maybe, but certainly a huge help on
these
> sparse bands!)
>
>
>
>
> Finally, could this same question be applied
> equally to RTTY, where it depends on the software used, despite long
> established rules for mark/space frequencies? If I use MixW, I can
keep my
> rig dial fixed and click on any of several signals in the passband,
> decoding them all equally (easy, certainly but not optimal). Is
this just
> the wrong way to use this software? Should the ACF be locked
centered
> between the standard RTTY M/S audio frequencies and the dial moved?
> Using MMTTY, the marker stays fixed and the dial is adjusted so
> it’s not a concern. Is one better than the other, personal
> preference, or rig dependent?
>
> R/
> Glenn KD4ULB
>
> > Bill Aycock wrote:
>
> >> Frank- I think that there is MUCH confusion in our ranks on
> this
> >> subject. For instance, I set my rig to one frequency
> (usually
> >> 14,070.00) and leave it there. I tune to different
> signals by moving
> >> the "marker" that shows the
> offset from the base frequency on the
> >> waterfall. The radio
> bandwidth is many times as wide as the signal
> >> width (for
> PSK31), and many signals can be accommodated in the
> >>
> passband. I have a tuneable Digital filter, and one of the most
> >> educational tricks is to shift the upper and lower audio limits
> of
> >> the filter, and watch the result on the waterfall One of
> the sources
> >> of the confusion is the ambiguity in the
> meaning of "best". I think
> >> that it is highly
> improbable that we can get a clear definition. Good
> >> luck-
> Bill-W4BSG
> >>
> >
> > In my opinion there are
> two "classes" of radios for digital use, and
> > which
> type you have dictates how you handle the center frequency
> >
> question. Older "legacy" radios do not allow use of narrow
> crystal
> > filters (originally intended for CW) in the digital
> modes. The
> > designers of these radios either ignored the digital
> modes altogether
> > (requiring, for example, interfacing the radio
> through the mic
> > connector) or simply didn't care much (my
> FT-900, an otherwise good
> > radio, falls into this category).
> These radios can be used for digital,
> > but lack the most
> important QRM-fighting tools--the crystal and
> > mechanical
> filters. For these radios you can get away with tuning by
> >
> leaving the VFO alone and simply "moving the marker" on the
> waterfall to
> > the signal you wish to receive. But you will miss
> receiving many, many
> > signals if the band is at all crowded if
> you tune using this technique.
> >
> > Newer radios
> generally all allow use of the narrow crystal and
> > mechanical
> filters in the digital modes and typically have a special
> >
> "DIGI" mode setting for this purpose. For radios of this type,
> it is
> > *very important* to tune the station that you are working
> to the center
> > frequency rather than simply moving the
> "marker" on the waterfall and
> > not touching the VFO.
> The reason is that otherwise you cannot use the
> > crystal and
> mechanical filters of your rig effectively. The optimal way
> > to
> tune a station with a modern rig is to place the received signal in
> > the center frequency passband, typically either 1000hz (most Yaesu
>
> > radios, for example) or 1500 hz, and then utilize the rig's
> narrow
> > filter. For PSK31, literally the narrower the better --
> for example, my
> > Mark V's 250hz filters are super for PSK modes,
> and the 500hz filters
> > are great for MFSK, 500hz Olivia, Domino,
> and MT63. Doing this also
> > makes the IF width and shift controls
> much more effective, and often you
> > can use these controls to
> eliminate even a QRMing signal that is inside
> > the narrow
> passband "corridor."
> >
> > Placing the received
> signal in the center frequency passband often makes
> > a huge
> difference in your ability to receive a signal. Often if there
> >
> is a strong PSK signal elsewhere on the band, it will desensitze
your
> > receiver through AGC action to the point where you are not
> receiving the
> > weaker signals at all. Kick in the narrow
> filters, and this problem
> > will disappear. This is true even
> with higher-end rigs such as the
> > FT1000MP/Mark V. Sure, you can
> work stations by simply moving the
> > "marker" to the
> station you want to work rather than tuning the same
> > station to
> your rig's center frequency, but this technique is
> > sub-optimal
> and makes the signal you wish to receive subject to QRM and
> > AGC
> desensitization even from signals 1Khz or more away.
> >
> >
> You can usually readily see how important 1) tuning the received
signal
>
> > to the center frequency and 2) kicking in the narrow filters
> actually
> > is, by watching the waterfall. Often the waterfall on
> the rig will be
> > dark when the passband is wide open, and much
> lighter on the received
> > signal once the filters are kicked in.
> This is because some stronger
> > signal outside of the filter
> passband is desensitizing the receiver. I
> > can often copy
> signals with the filters in the circuit that are
> > completely
> invisible on the waterfall without the filters.
> >
> > The
> best digital programs recognize the importance of tuning the
> >
> received signal to the center passband frequency, and make this
easy to
>
> > do. DM780 has a center frequency marker, and with one click of
> an icon
> > it automatically tunes the received signal to the
> center passband (moves
> > the received signal "marker"
> to the "C" center frequency marker). One
> > more click
> and you can kick in whichever narrow filters your rig has
> > that
> are appropriate for the mode, e.g. 500hz for MFSK, much narrower
> > for PSK. MixW also enables the user to do this with a few clicks
by
> use
> > of an easy-to-program macro function.
> >
> >
> As the band conditions start to improve, with more signals on the
band
> > (remember, we are presently right at the solar minimum) using the
> narrow
> > filters on digital modes will become more and more
> important.
> >
> > de Roger, W6VZV
> >
> >
> >
> > Announce your digital presence via our Interactive Sked
> Page at
> > http://www.obriensweb.com/drsked/drsked.php
> >
>
> > Yahoo! Groups Links
> >
> http://groups.yahoo.com/group/digitalradio/
> >
> >
> >
> ID required)
> >
> > mailto:[EMAIL PROTECTED]
> >
> mailto:[EMAIL PROTECTED]
> >
> >
> [EMAIL PROTECTED]
> >
> http://docs.yahoo.com/info/terms/
> >
> >
>
