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Re: [digsstv] Transmitting Pictures

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  • jdow
    1) PSK-31 will work better at about 25% to 33% rather than 50% and you must reduce the power with the line input drive not the ALC. (ALC is generally not fast
    Message 1 of 5 , May 30 6:03 AM
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      1) PSK-31 will work better at about 25% to 33% rather than 50% and you
      must reduce the power with the line input drive not the ALC. (ALC is
      generally not fast enough to cut power for the peaks properly. YMMV.
      Tests I made with my ProII and an instrumented WinPSK suggest that
      the ProII ALC was not as good a tool for cutting power output for
      PSK-31 as was cutting the signal input with the ALC left full up.)

      2) EasyPAL is in the same category. It is a very "peaky" signal. And a
      lot of information is in those peaks. So if they get clipped the
      signal decoding suffers greatly.

      {^_^} Joanne, W6MKU
      ----- Original Message -----
      From: "rickprice407" <no_reply@yahoogroups.com>
      To: <digsstv@yahoogroups.com>
      Sent: Friday, 2009/May/29 06:03
      Subject: [digsstv] Transmitting Pictures


      >I recently got into Digital SSTV and finally was able to receive a few
      >pictures using Easypal. Now I'd like to send some as well.
      >
      > I'm using an IC-746Pro. I know for PSK-31, RTTY and other didtal modes, I
      > have to reduce my power output setting to about 50% of max. Do I need to
      > do that as well if I am sending pictures? I know i don't with regular
      > SSTV.
      >
      > Any help appreciated.
      >
      > Rick Price
      > KC4RP
      >
      >
      >
      > ------------------------------------
      >
      > Yahoo! Groups Links
      >
      >
      >
    • jdow
      Garrett, there is a range of signal levels at which the decoding loss from clipping is traded off against higher power over all. For best decoding efficiency
      Message 2 of 5 , May 30 6:10 AM
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        Garrett, there is a range of signal levels at which the decoding loss from
        clipping is traded off against higher power over all. For best decoding
        efficiency you want very low power. But 25% might be a workable compromise
        if you are willing to tolerate a higher than necessary minimum error rate
        when signals are really good. It also depends a GREAT deal on your PA's
        clipping performance. If it's being run class-A it might do well at 50%
        while an AB1 or AB2 PA would perform very poorly at that sort of level.

        (Most PAs are designed for SSB voice service where some clipping is seen
        merely as splatter and you still get through just fine. Some contest rigs
        are designed to minimize that splatter (IMD) for multi-operator setups.
        The former wants the 10% to 15% power setting while the latter may take
        the 50% setting. It is rather fun to watch reducing drive to the PA
        stages of the rig improve received signal to noise ratio (decoded accuracy)
        as a vindication of all that ugly math I studied years ago in comm theory
        classes.)

        {^_^} Joanne, W6MKU
        ----- Original Message -----
        From: "AA0OI" <aa0oi@...>
        Sent: Saturday, 2009/May/30 05:16


        Hi Rick:
        Most havve found that by setting the output power by using the ALC on the
        radio is the way to go.. start sending and reduce the alc setting on the
        radio just to the point where it shows NONE... Power output should show now
        more than 15 to 20 watts... There is nothing set in stone,, on my Yahoo
        ft990 my alc shows about 1/2 and output to the amp shows 50 watts.. but this
        seems to be the exception, and not the rule..
        Just get someone to monitor your transmittion and send a "test tone" to make
        sure your not overdriving..
        Then try 20 to 30 sec of a picture and have receiving station check your snr
        and see if they are getting a
        green line at the bottom and the beginings of a picture..

        Garrett / AA0OI




        ________________________________
        From: rickprice407 <no_reply@yahoogroups.com>
        To: digsstv@yahoogroups.com
        Sent: Friday, May 29, 2009 8:03:58 AM
        Subject: [digsstv] Transmitting Pictures





        I recently got into Digital SSTV and finally was able to receive a few
        pictures using Easypal. Now I'd like to send some as well.

        I'm using an IC-746Pro. I know for PSK-31, RTTY and other didtal modes, I
        have to reduce my power output setting to about 50% of max. Do I need to do
        that as well if I am sending pictures? I know i don't with regular SSTV.

        Any help appreciated.

        Rick Price
        KC4RP
      • AA0OI
        Hi Joanne: I know it does not make any sense, but after testing with my radio and set up and testing this program for better than  years,, I knnow.  we have
        Message 3 of 5 , May 30 3:38 PM
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          Hi Joanne:
          I know it does not make any sense, but after testing with my radio and set up and testing this program for better than  years,, I knnow.  we have test for hour on end  day after day.. Mine is just different ,, we have tried it everyway  ( my radio- for some reason puts out  125 watts and has from day one -on external watt meter and radio meter..This is only one of my radios,,, and the only one that acts this way....
           
          Garrett / AA0OI



          From: jdow <jdow@...>
          To: digsstv@yahoogroups.com
          Sent: Saturday, May 30, 2009 8:10:32 AM
          Subject: Re: [digsstv] Transmitting Pictures

          Garrett, there is a range of signal levels at which the decoding loss from
          clipping is traded off against higher power over all. For best decoding
          efficiency you want very low power. But 25% might be a workable compromise
          if you are willing to tolerate a higher than necessary minimum error rate
          when signals are really good. It also depends a GREAT deal on your PA's
          clipping performance. If it's being run class-A it might do well at 50%
          while an AB1 or AB2 PA would perform very poorly at that sort of level.

          (Most PAs are designed for SSB voice service where some clipping is seen
          merely as splatter and you still get through just fine. Some contest rigs
          are designed to minimize that splatter (IMD) for multi-operator setups.
          The former wants the 10% to 15% power setting while the latter may take
          the 50% setting. It is rather fun to watch reducing drive to the PA
          stages of the rig improve received signal to noise ratio (decoded accuracy)
          as a vindication of all that ugly math I studied years ago in comm theory
          classes.)

          {^_^} Joanne, W6MKU

          ----- Original Message -----
          From: "AA0OI" <aa0oi@yahoo. com>
          Sent: Saturday, 2009/May/30 05:16

          Hi Rick:
          Most havve found that by setting the output power by using the ALC on the
          radio is the way to go.. start sending and reduce the alc setting on the
          radio just to the point where it shows NONE... Power output should show now
          more than 15 to 20 watts... There is nothing set in stone,, on my Yahoo
          ft990 my alc shows about 1/2 and output to the amp shows 50 watts.. but this
          seems to be the exception, and not the rule..
          Just get someone to monitor your transmittion and send a "test tone" to make
          sure your not overdriving. .
          Then try 20 to 30 sec of a picture and have receiving station check your snr
          and see if they are getting a
          green line at the bottom and the beginings of a picture..

          Garrett / AA0OI

          ____________ _________ _________ __
          From: rickprice407 <no_reply@yahoogroup s.com>
          To: digsstv@yahoogroups .com
          Sent: Friday, May 29, 2009 8:03:58 AM
          Subject: [digsstv] Transmitting Pictures

          I recently got into Digital SSTV and finally was able to receive a few
          pictures using Easypal. Now I'd like to send some as well.

          I'm using an IC-746Pro. I know for PSK-31, RTTY and other didtal modes, I
          have to reduce my power output setting to about 50% of max. Do I need to do
          that as well if I am sending pictures? I know i don't with regular SSTV.

          Any help appreciated.

          Rick Price
          KC4RP


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