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Center of the waterfall question

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  • Gunner
    This topic was started in the digitalradio group but got no where. I ve posted it here to see what this group does with it. The initial question is at the top,
    Message 1 of 5 , Oct 2, 2007
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      This topic was started in the digitalradio group but got no where. I've
      posted it here to see what this group does with it.

      The initial question is at the top, with resulting replies below. Its a
      bit of a long read but the topic is important to Olivia users as well as
      other, similar modes.
      ===================================================

      > 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
      ---------------------------------------------------
      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
    • Waldis Jirgens
      Hi Gunner, Yes it IS a long read and expressed in a VERY complicated way. As I see it: Problem: Desensing by strong adjacent signals. Solution: Use sharp
      Message 2 of 5 , Oct 3, 2007
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        Hi Gunner,

        Yes it IS a long read and expressed in a VERY complicated way. As I see it:

        Problem: Desensing by strong adjacent signals.
        Solution: Use sharp filters.

        I have 2 old rigs: A TS50S and a IC706Mk2 with 500Hz and 250Hz CW
        filters respectively. The TS50 allows outright use of the CW filer in
        SSB mode, the IC706Mk2 needs a trick (declare the CW filter as a narrow
        SSB filter in set-up). I can shift the filter passband with IF shift, so
        normally I tune by clicking; if a station is too far off QRG I do a real
        QSY.

        I find it very hard to believe that more modern rigs don't allow
        effective filter use other than smack bang in the center of the
        passband. But if that's the price that the owners of these "modern" rigs
        have to pay for decent reception - so be it, serves them right >>;->==

        --
        73: Waldis Jirgens - VK1WJ -
        http://mywebpage.netscape.com/ilgonis/index.html



        Gunner wrote:
        > This topic was started in the digitalradio group but got no where. I've
        > posted it here to see what this group does with it.
        >
        > The initial question is at the top, with resulting replies below. Its a
        > bit of a long read but the topic is important to Olivia users as well as
        > other, similar modes.
      • Andrew O'Brien
        The standard method is to QSY the radio via the command that many software applications call align or center . So , if my center frequency is 1500Hz on a
        Message 3 of 5 , Oct 3, 2007
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          The standard method is to "QSY" the radio via the command that many
          software applications call "align" or "center". So , if my center
          frequency is 1500Hz on a waterfall and I see a Olivia signal at 2700
          Hz, I click on that signal...lock on to it..., and activate the align
          command to change the frequency on the rig so that the audio frequency
          is 1500 hz on the waterfall.
          In fact, I invented this method! Well, that is really a bit of a
          stretch ...but when alpha testing some PSK31 software in the very
          early days of PSK31, I mentioned to the author that it would be nice
          if we could QSY the radio rather than just wander up and down the
          audio frequencies of the waterfall. Within an hour of the suggestion
          the author released a new version with that feature, the first of any
          PSK31 software.
          Andy K3UK


          On 10/3/07, Waldis Jirgens <waldis@...> wrote:
          > Hi Gunner,
          >
          > Yes it IS a long read and expressed in a VERY complicated way. As I see it:
          >
          > Problem: Desensing by strong adjacent signals.
          > Solution: Use sharp filters.
          >
          > I have 2 old rigs: A TS50S and a IC706Mk2 with 500Hz and 250Hz CW
          > filters respectively. The TS50 allows outright use of the CW filer in
          > SSB mode, the IC706Mk2 needs a trick (declare the CW filter as a narrow
          > SSB filter in set-up). I can shift the filter passband with IF shift, so
          > normally I tune by clicking; if a station is too far off QRG I do a real
          > QSY.
          >
          > I find it very hard to believe that more modern rigs don't allow
          > effective filter use other than smack bang in the center of the
          > passband. But if that's the price that the owners of these "modern" rigs
          > have to pay for decent reception - so be it, serves them right >>;->==
          >
          > --
          > 73: Waldis Jirgens - VK1WJ -
          > http://mywebpage.netscape.com/ilgonis/index.html
          >
          >
          >
          > Gunner wrote:
          > > This topic was started in the digitalradio group but got no where. I've
          > > posted it here to see what this group does with it.
          > >
          > > The initial question is at the top, with resulting replies below. Its a
          > > bit of a long read but the topic is important to Olivia users as well as
          > > other, similar modes.
          >
          >
          > --
          > CQ Frequency Olivia 500/16 = 14076.4kHz (center)
          > OliviaData Group web site http://groups.yahoo.com/group/oliviadata
          > Olivia Frequencies and Information web site http://hflink.com/olivia/
          > To change message delivery: http://groups.yahoo.com/group/oliviadata/join
          > To stop email, send an email to: oliviadata-nomail@yahoogroups.com
          > --
          >
          >
          >
          >
          >
          >
          >
          >
          >
          >
          >
          >
          >
          >
          > .
          >
          >
          > Yahoo! Groups Links
          >
          >
          >
          >


          --
          Andy K3UK
          www.obriensweb.com
          (QSL via N2RJ)
        • aa4pb@verizon.net
          I think the issue is whether you want to use the receiver s narrow IF filter or not. If you are not having a receiver desense problem then leave the radio dial
          Message 4 of 5 , Oct 3, 2007
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            I think the issue is whether you want to use the receiver's narrow IF filter or not. If you are not having a receiver desense problem then leave the radio dial fixed and move your signal around the passband. If you want to use the narrow filter then you must center the signal in the passband.

            If you have MixW and a CAT controlled radio then you can have the best of both worlds. A macro can be set up to automatically change the filters and retune the radio to center the signal in the passband and another to return it automatically to the original settings.
          • Waldis Jirgens
            ... Desensing will always happen with strong adjacent signals. The problem here seems to be the inability of some modern rigs to perform a simple if shift
            Message 5 of 5 , Oct 3, 2007
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              aa4pb@... wrote:
              >
              >
              > I think the issue is whether you want to use the receiver's narrow IF
              > filter or not. If you are not having a receiver desense problem then
              > leave the radio dial fixed and move your signal around the passband. If
              > you want to use the narrow filter then you must center the signal in the
              > passband.

              Desensing will always happen with strong adjacent signals. The problem
              here seems to be the inability of some "modern" rigs to perform a simple
              "if shift" when using a narrow filter. Most "less modern" rigs can do
              that, so the whole question does not arise.

              --
              73: Waldis Jirgens - VK1WJ -
              http://mywebpage.netscape.com/ilgonis/index.html
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