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RE: RE: Scan!

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  • radiotech750
    So in reality the RF?scan function is useless? If I have to turn the RF gain down so far to get it to scan that it rolls by most stations then why is the scan
    Message 1 of 19 , Sep 10, 2013
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      So in reality the RF?scan function is useless? If I have to turn the RF gain down so far to get it to scan that it rolls by most stations then why is the scan feature even there?

      Ernie

       



      --- In RADIOSHACKDX394@yahoogroups.com, <radioshackdx394@yahoogroups.com> wrote:

      Ernie...


      With the "stock" DX-394 RF Gain control, whether on the whip or an external antenna, you would have to turn the RF Gain past the half-way, 12-O Clock, position to REALLY begin reducing RF Gain to be "missing" the weaker ones.


      Anything up to that position, going from full on counter-clockwise (full gain) to the 12 -O Clock position really doesn't reduce gain all THAT much, but some, of course, roughly about 30-40% on the 394's seen here and on mine.


      One of the 394 mods replaces the stock RF Gain control ( a standard logarithmic taper) with a rarer linear carbon pot. Yet, the effects of this practice seem not radically improved at least on the three units I have seen here where that mod was done, one reason that I decline for now to mod mine.


      Joe



      --- In RADIOSHACKDX394@yahoogroups.com, <radioshackdx394@yahoogroups.com> wrote:

      When I want to scan I have to turn my RF gain down to about 8 o'clock. I know I am missing some of the weaker ones. Is there a way to allow more RF gain and still scan? Is it my noisy location or antenna?
      Any ideas?

      Thanks
      Ernie
    • josephrot
      Ernie... Hmm, giving more thought, occasionally on the 41m band, the scan on my humble DX-394 seems to can not work, as strong AM (amateurs using AM as
      Message 2 of 19 , Sep 11, 2013
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        Ernie...

         

        Hmm, giving more thought, occasionally on the 41m band, the scan on my humble DX-394 seems to "can not" work, as strong AM (amateurs using AM as opposed to SSB) signal "over-rides" the weaker SSB signals.

         

        That's one of the only conditions that I have seen here where the RF Scan seems to fail, other than one time R. Havana at 6.000 was coming in so strong that it both pinned the "S" meter LCD and swamped the front-end, until I turned down the RF Gain quite a bit. Only then did the RF Scan start to work again.. Agreed, there may be other times it may fail, but these two "situations" stand out.

         

        Not sure if that might be a possibility in your location, but hoping mentioning what I see and hear from time to time here (Knoxville, TN / USA) may be of assistance.

         

        Joe



        --- In RADIOSHACKDX394@yahoogroups.com, <radioshackdx394@yahoogroups.com> wrote:

        So in reality the RF?scan function is useless? If I have to turn the RF gain down so far to get it to scan that it rolls by most stations then why is the scan feature even there?

        Ernie

         



        --- In RADIOSHACKDX394@yahoogroups.com, <radioshackdx394@yahoogroups.com> wrote:

        Ernie...


        With the "stock" DX-394 RF Gain control, whether on the whip or an external antenna, you would have to turn the RF Gain past the half-way, 12-O Clock, position to REALLY begin reducing RF Gain to be "missing" the weaker ones.


        Anything up to that position, going from full on counter-clockwise (full gain) to the 12 -O Clock position really doesn't reduce gain all THAT much, but some, of course, roughly about 30-40% on the 394's seen here and on mine.


        One of the 394 mods replaces the stock RF Gain control ( a standard logarithmic taper) with a rarer linear carbon pot. Yet, the effects of this practice seem not radically improved at least on the three units I have seen here where that mod was done, one reason that I decline for now to mod mine.


        Joe



        --- In RADIOSHACKDX394@yahoogroups.com, <radioshackdx394@yahoogroups.com> wrote:

        When I want to scan I have to turn my RF gain down to about 8 o'clock. I know I am missing some of the weaker ones. Is there a way to allow more RF gain and still scan? Is it my noisy location or antenna?
        Any ideas?

        Thanks
        Ernie
      • Radionut R
        Thanks Joe I thinks my noisy location has some to do with it! Ernie ... -- Remember that when you think you have it all figured out... you wake up to start all
        Message 3 of 19 , Sep 12, 2013
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          Thanks Joe
          I thinks my noisy location has some to do with it!

          Ernie


          On Wed, Sep 11, 2013 at 10:00 PM, <joerotello@...> wrote:
           

          Ernie...

           

          Hmm, giving more thought, occasionally on the 41m band, the scan on my humble DX-394 seems to "can not" work, as strong AM (amateurs using AM as opposed to SSB) signal "over-rides" the weaker SSB signals.

           

          That's one of the only conditions that I have seen here where the RF Scan seems to fail, other than one time R. Havana at 6.000 was coming in so strong that it both pinned the "S" meter LCD and swamped the front-end, until I turned down the RF Gain quite a bit. Only then did the RF Scan start to work again.. Agreed, there may be other times it may fail, but these two "situations" stand out.

           

          Not sure if that might be a possibility in your location, but hoping mentioning what I see and hear from time to time here (Knoxville, TN / USA) may be of assistance.

           

          Joe



          --- In RADIOSHACKDX394@yahoogroups.com, <radioshackdx394@yahoogroups.com> wrote:

          So in reality the RF?scan function is useless? If I have to turn the RF gain down so far to get it to scan that it rolls by most stations then why is the scan feature even there?

          Ernie

           



          --- In RADIOSHACKDX394@yahoogroups.com, <radioshackdx394@yahoogroups.com> wrote:

          Ernie...


          With the "stock" DX-394 RF Gain control, whether on the whip or an external antenna, you would have to turn the RF Gain past the half-way, 12-O Clock, position to REALLY begin reducing RF Gain to be "missing" the weaker ones.


          Anything up to that position, going from full on counter-clockwise (full gain) to the 12 -O Clock position really doesn't reduce gain all THAT much, but some, of course, roughly about 30-40% on the 394's seen here and on mine.


          One of the 394 mods replaces the stock RF Gain control ( a standard logarithmic taper) with a rarer linear carbon pot. Yet, the effects of this practice seem not radically improved at least on the three units I have seen here where that mod was done, one reason that I decline for now to mod mine.


          Joe



          --- In RADIOSHACKDX394@yahoogroups.com, <radioshackdx394@yahoogroups.com> wrote:

          When I want to scan I have to turn my RF gain down to about 8 o'clock. I know I am missing some of the weaker ones. Is there a way to allow more RF gain and still scan? Is it my noisy location or antenna?
          Any ideas?

          Thanks
          Ernie




          --
          Remember that when you think you have it all figured out... you wake up to start all over again!
          Trust yourself and MOST times you will not be disappointed
        • Tom H
          Indeed, strong noise interference between carriers interferes with the scan detection of desired signals. And the scanner does not work very well either for
          Message 4 of 19 , Sep 12, 2013
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            Indeed, strong noise interference between carriers interferes with the scan detection of desired signals. And the scanner does not work very well either for signals without a single strong carrier, such as SSB.

            After all, what is it that causes the scanner to stop on a frequency? It is the AGC voltage (S-meter) crossing a defined threshold. The AGC is measured by an A-D converter which is compared to a number in firmware while the micro controller is frequency scanning. When that number is exceeded, the micro controller stops scanning.

            When you vary RF Gain, you affect how hard the AGC is driven. When you back off gain, naturally only the strongest signals move the S-meter and will stop the scan. At max gain, noise alone may move the s-meter sufficiently to stop the scan.

            SSB moves the S-meter only when there is modulation and it moves proportionately to the intensity of the modulation. Thus the scanner may tune through a SSB signal between words or syllables or during soft consonants without detecting a signal. Even if it did detect a signal, the probability that it will be tuned in correctly is rather small.

            In general, any AGC controlled scanning trigger is not going to be very effective in noisy conditions or for SSB. Its usefulness improves above around 10 MHz as noise abates. Applications for the DX-394 might include monitoring for band openings on the upper SWBC bands and the CB, both of which still have much unsuppressed carrier amplitude modulation signals.

            Tom ve3meo

            --- In RADIOSHACKDX394@yahoogroups.com, Radionut R <ranger2995@...> wrote:
            >
            > Thanks Joe
            > I thinks my noisy location has some to do with it!
            >
            > Ernie
            >
          • William Barrett
            This won t help, but I ve never seen a scanner in an HF receiver work like it should. There is just too much static and the signals cover a vast dynamic range
            Message 5 of 19 , Sep 13, 2013
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              This won't help, but I've never seen a scanner in an HF receiver work like it should.
              There is just too much static and the signals cover a vast dynamic range of strengths.
               
                73
              KW1B
                NC
               
              -----Original Message-----
              From: RADIOSHACKDX394@yahoogroups.com [mailto:RADIOSHACKDX394@yahoogroups.com]On Behalf Of Tom H
              Sent: Thursday, September 12, 2013 22:12
              To: RADIOSHACKDX394@yahoogroups.com
              Subject: [RADIOSHACKDX394] Re: RE: RE: Scan!

                  

              Indeed, strong noise interference between carriers interferes with the scan detection of desired signals. And the scanner does not work very well either for signals without a single strong carrier, such as SSB.

              After all, what is it that causes the scanner to stop on a frequency? It is the AGC voltage (S-meter) crossing a defined threshold. The AGC is measured by an A-D converter which is compared to a number in firmware while the micro controller is frequency scanning. When that number is exceeded, the micro controller stops scanning.

              When you vary RF Gain, you affect how hard the AGC is driven. When you back off gain, naturally only the strongest signals move the S-meter and will stop the scan. At max gain, noise alone may move the s-meter sufficiently to stop the scan.

              SSB moves the S-meter only when there is modulation and it moves proportionately to the intensity of the modulation. Thus the scanner may tune through a SSB signal between words or syllables or during soft consonants without detecting a signal. Even if it did detect a signal, the probability that it will be tuned in correctly is rather small.

              In general, any AGC controlled scanning trigger is not going to be very effective in noisy conditions or for SSB. Its usefulness improves above around 10 MHz as noise abates. Applications for the DX-394 might include monitoring for band openings on the upper SWBC bands and the CB, both of which still have much unsuppressed carrier amplitude modulation signals.

              Tom ve3meo

              --- In RADIOSHACKDX394@yahoogroups.com, Radionut R <ranger2995@...> wrote:
              >
              > Thanks Joe
              > I thinks my noisy location has some to do with it!
              >
              > Ernie
              >

            • Ernie Rice
              Darn! Too bad. Nice feature but useless. Ernie Sent from my iPhone
              Message 6 of 19 , Sep 13, 2013
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                Darn! Too bad. Nice feature but useless. 

                Ernie

                Sent from my iPhone

                On Sep 13, 2013, at 17:17, "William Barrett" <wbarrett@...> wrote:

                 

                This won't help, but I've never seen a scanner in an HF receiver work like it should.
                There is just too much static and the signals cover a vast dynamic range of strengths.
                 
                  73
                KW1B
                  NC
                 
                -----Original Message-----
                From: RADIOSHACKDX394@yahoogroups.com [mailto:RADIOSHACKDX394@yahoogroups.com]On Behalf Of Tom H
                Sent: Thursday, September 12, 2013 22:12
                To: RADIOSHACKDX394@yahoogroups.com
                Subject: [RADIOSHACKDX394] Re: RE: RE: Scan!

                    

                Indeed, strong noise interference between carriers interferes with the scan detection of desired signals. And the scanner does not work very well either for signals without a single strong carrier, such as SSB.

                After all, what is it that causes the scanner to stop on a frequency? It is the AGC voltage (S-meter) crossing a defined threshold. The AGC is measured by an A-D converter which is compared to a number in firmware while the micro controller is frequency scanning. When that number is exceeded, the micro controller stops scanning.

                When you vary RF Gain, you affect how hard the AGC is driven. When you back off gain, naturally only the strongest signals move the S-meter and will stop the scan. At max gain, noise alone may move the s-meter sufficiently to stop the scan.

                SSB moves the S-meter only when there is modulation and it moves proportionately to the intensity of the modulation. Thus the scanner may tune through a SSB signal between words or syllables or during soft consonants without detecting a signal. Even if it did detect a signal, the probability that it will be tuned in correctly is rather small.

                In general, any AGC controlled scanning trigger is not going to be very effective in noisy conditions or for SSB. Its usefulness improves above around 10 MHz as noise abates. Applications for the DX-394 might include monitoring for band openings on the upper SWBC bands and the CB, both of which still have much unsuppressed carrier amplitude modulation signals.

                Tom ve3meo

                --- In RADIOSHACKDX394@yahoogroups.com, Radionut R <ranger2995@...> wrote:
                >
                > Thanks Joe
                > I thinks my noisy location has some to do with it!
                >
                > Ernie
                >

              • Tom H
                A phase detector such as the tuning meter for a VHF-FM receiver might be a superior sensor for detection of a carrier than AGC. I don t know if it has ever
                Message 7 of 19 , Sep 13, 2013
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                  A phase detector such as the tuning meter for a VHF-FM receiver might be a superior sensor for detection of a carrier than AGC. I don't know if it has ever been implemented in an hf receiver so maybe its an idea that has been tried and discarded. Do sync-AM receivers have effective scanners? Maybe scan speed would have to be very slow.

                  Tom

                  --- In RADIOSHACKDX394@yahoogroups.com, "William Barrett" <wbarrett@...> wrote:
                  >
                  > This won't help, but I've never seen a scanner in an HF receiver work like
                  > it should.
                  > There is just too much static and the signals cover a vast dynamic range of
                  > strengths.
                  >
                  > 73
                  > KW1B
                • William Barrett
                  Squelch on an HF receiver works very poorly, too. I will say this: both squelch and scan will work -- sorta -- if you do two things: [1] Only expect it to
                  Message 8 of 19 , Sep 14, 2013
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                    Squelch on an HF receiver works very poorly, too.
                     
                    I will say this: both squelch and scan will work -- sorta -- if you do two things:
                     
                    [1]  Only expect it to work with VERY strong signals WAY above the noise floor.
                     
                    [2]  Reduce the RF gain as much as possible consistent with still hearing the signal.
                          What this does is back you off the AGC level-seeking curve, and make any signal
                          present pop way above the noise floor.  Now for AM, this is fine.  For SSB, all
                          you expect is to hear the squelch popping and pumping on voice peaks -- you'll
                          have to manually turn the squelch off, or stop the scan to hear it right.
                     
                      73
                    KW1B
                      NC
                     
                     
                    -----Original Message-----
                    From: RADIOSHACKDX394@yahoogroups.com [mailto:RADIOSHACKDX394@yahoogroups.com]On Behalf Of Ernie Rice
                    Sent: Friday, September 13, 2013 18:30
                    To: RADIOSHACKDX394@yahoogroups.com
                    Subject: Re: [RADIOSHACKDX394] Re: RE: RE: Scan!

                     

                    Darn! Too bad. Nice feature but useless. 

                    Ernie

                    Sent from my iPhone

                    On Sep 13, 2013, at 17:17, "William Barrett" <wbarrett@...> wrote:

                     

                    This won't help, but I've never seen a scanner in an HF receiver work like it should.
                    There is just too much static and the signals cover a vast dynamic range of strengths.
                     
                      73
                    KW1B
                      NC
                     
                    -----Original Message-----
                    From: RADIOSHACKDX394@yahoogroups.com [mailto:RADIOSHACKDX394@yahoogroups.com]On Behalf Of Tom H
                    Sent: Thursday, September 12, 2013 22:12
                    To: RADIOSHACKDX394@yahoogroups.com
                    Subject: [RADIOSHACKDX394] Re: RE: RE: Scan!

                        

                    Indeed, strong noise interference between carriers interferes with the scan detection of desired signals. And the scanner does not work very well either for signals without a single strong carrier, such as SSB.

                    After all, what is it that causes the scanner to stop on a frequency? It is the AGC voltage (S-meter) crossing a defined threshold. The AGC is measured by an A-D converter which is compared to a number in firmware while the micro controller is frequency scanning. When that number is exceeded, the micro controller stops scanning.

                    When you vary RF Gain, you affect how hard the AGC is driven. When you back off gain, naturally only the strongest signals move the S-meter and will stop the scan. At max gain, noise alone may move the s-meter sufficiently to stop the scan.

                    SSB moves the S-meter only when there is modulation and it moves proportionately to the intensity of the modulation. Thus the scanner may tune through a SSB signal between words or syllables or during soft consonants without detecting a signal. Even if it did detect a signal, the probability that it will be tuned in correctly is rather small.

                    In general, any AGC controlled scanning trigger is not going to be very effective in noisy conditions or for SSB. Its usefulness improves above around 10 MHz as noise abates. Applications for the DX-394 might include monitoring for band openings on the upper SWBC bands and the CB, both of which still have much unsuppressed carrier amplitude modulation signals.

                    Tom ve3meo

                    --- In RADIOSHACKDX394@yahoogroups.com, Radionut R <ranger2995@...> wrote:
                    >
                    > Thanks Joe
                    > I thinks my noisy location has some to do with it!
                    >
                    > Ernie
                    >

                  • Ernie Rice
                    Great info!! Ernie Sent from my iPhone ... Great info!! Ernie Sent from my iPhone On Sep 14, 2013, at 8:55, William Barrett
                    Message 9 of 19 , Sep 14, 2013
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                      Great info!! 

                      Ernie

                      Sent from my iPhone

                      On Sep 14, 2013, at 8:55, "William Barrett" <wbarrett@...> wrote:

                       

                      

                      Squelch on an HF receiver works very poorly, too.
                       
                      I will say this: both squelch and scan will work -- sorta -- if you do two things:
                       
                      [1]  Only expect it to work with VERY strong signals WAY above the noise floor.
                       
                      [2]  Reduce the RF gain as much as possible consistent with still hearing the signal.
                            What this does is back you off the AGC level-seeking curve, and make any signal
                            present pop way above the noise floor.  Now for AM, this is fine.  For SSB, all
                            you expect is to hear the squelch popping and pumping on voice peaks -- you'll
                            have to manually turn the squelch off, or stop the scan to hear it right.
                       
                        73
                      KW1B
                        NC
                       
                       
                      -----Original Message-----
                      From: RADIOSHACKDX394@yahoogroups.com [mailto:RADIOSHACKDX394@yahoogroups.com]On Behalf Of Ernie Rice
                      Sent: Friday, September 13, 2013 18:30
                      To: RADIOSHACKDX394@yahoogroups.com
                      Subject: Re: [RADIOSHACKDX394] Re: RE: RE: Scan!

                       

                      Darn! Too bad. Nice feature but useless. 

                      Ernie

                      Sent from my iPhone

                      On Sep 13, 2013, at 17:17, "William Barrett" <wbarrett@...> wrote:

                       

                      This won't help, but I've never seen a scanner in an HF receiver work like it should.
                      There is just too much static and the signals cover a vast dynamic range of strengths.
                       
                        73
                      KW1B
                        NC
                       
                      -----Original Message-----
                      From: RADIOSHACKDX394@yahoogroups.com [mailto:RADIOSHACKDX394@yahoogroups.com]On Behalf Of Tom H
                      Sent: Thursday, September 12, 2013 22:12
                      To: RADIOSHACKDX394@yahoogroups.com
                      Subject: [RADIOSHACKDX394] Re: RE: RE: Scan!

                          

                      Indeed, strong noise interference between carriers interferes with the scan detection of desired signals. And the scanner does not work very well either for signals without a single strong carrier, such as SSB.

                      After all, what is it that causes the scanner to stop on a frequency? It is the AGC voltage (S-meter) crossing a defined threshold. The AGC is measured by an A-D converter which is compared to a number in firmware while the micro controller is frequency scanning. When that number is exceeded, the micro controller stops scanning.

                      When you vary RF Gain, you affect how hard the AGC is driven. When you back off gain, naturally only the strongest signals move the S-meter and will stop the scan. At max gain, noise alone may move the s-meter sufficiently to stop the scan.

                      SSB moves the S-meter only when there is modulation and it moves proportionately to the intensity of the modulation. Thus the scanner may tune through a SSB signal between words or syllables or during soft consonants without detecting a signal. Even if it did detect a signal, the probability that it will be tuned in correctly is rather small.

                      In general, any AGC controlled scanning trigger is not going to be very effective in noisy conditions or for SSB. Its usefulness improves above around 10 MHz as noise abates. Applications for the DX-394 might include monitoring for band openings on the upper SWBC bands and the CB, both of which still have much unsuppressed carrier amplitude modulation signals.

                      Tom ve3meo

                      --- In RADIOSHACKDX394@yahoogroups.com, Radionut R <ranger2995@...> wrote:
                      >
                      > Thanks Joe
                      > I thinks my noisy location has some to do with it!
                      >
                      > Ernie
                      >

                    • josephrot
                      William... Tend to agree, but not on all HF receivers. Kenwood R-5000 is decent, of course at what the R-5000 costs, Grundig S750/Tecsun S2000 is decently
                      Message 10 of 19 , Sep 14, 2013
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                        William...

                         

                        Tend to agree, but not on all HF receivers. Kenwood R-5000 is decent, of course at what the R-5000 costs, Grundig S750/Tecsun S2000 is decently done, useful over most all conditions, there may be othetrs....and the HF Squelch on the Satellite 800/HAM2000 receivers works superbly, however relegated to the VHF bands but can be "mod" to cover FM as well.


                        Yet, agreed...the conditions that Squelch must operate over tend to be manifold if not extreme, to say the least, and definitely agreed, conditions are ripe to causing Squelch to work, not work, work well for a while, etc.


                        Conditions #1 and #2 in your reply frankly do not always apply to all the above noted receivers, but to a few and many others.


                        Joe

                         

                         <<  William Barrett stated:

                         

                        Squelch on an HF receiver works very poorly, too.

                        I will say this: both squelch and scan will work -- sorta -- if you do two things:
                         

                        [1]  Only expect it to work with VERY strong signals WAY above the noise floor.

                         
                        [2]  Reduce the RF gain as much as possible consistent with still hearing the signal.

                              What this does is back you off the AGC level-seeking curve, and make any signal

                              present pop way above the noise floor.  Now for AM, this is fine.  For SSB, all

                              you expect is to hear the squelch popping and pumping on voice peaks -- you'll

                              have to manually turn the squelch off, or stop the scan to hear it right.

                         
                          73

                        KW1B

                         

                          NC >> 

                      • Tom Holden
                        The AGC time constants affect scan response. If the attack is very slow and scan speed very fast, the receiver will tune right through without stopping. If
                        Message 11 of 19 , Sep 14, 2013
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                          The AGC time constants affect scan response. If the attack is very slow and scan speed very fast, the receiver will tune right through without stopping. If release is very slow and scan step very small, it takes many pushes of the start scanning button to get the radio to leave a strong signal behind and get on with scanning. 

                          One of the simpler AGC mods for the DX-394 has the effect of slowing both attack and release time constants, thus having adverse effect on scan operation. While that behaviour has benefit in reducing distortion due to the AGC tracking the modulation, it would be preferable if the AGC was fast for scanning and slow for listening. Motivated by listening rather than scanning issues, I developed AGC mods that, with front panel switches, provided fast attack with three release speeds and AGC on/off. I could manually choose fast release for scanning and slow release for listening. 

                          Until now, I had not thought about the desirability of a mod that would automatically switch to fast AGC when scanning is initiated. It's of little interest to me - just an idea - and I'm not sure there are hooks in the control system that would make feasible such a mod. 

                          Another mod I had explored had the effect of making the S-meter "hotter" which also had some beneficial effect for scanning. It was described at message 2937 http://groups.yahoo.com/group/RADIOSHACKDX394/message/2937

                          Tom ve3meo



                          On 2013-09-14, at 9:55 AM, "William Barrett" <wbarrett@...> wrote:

                           

                          

                          Squelch on an HF receiver works very poorly, too.
                           
                          I will say this: both squelch and scan will work -- sorta -- if you do two things:
                           
                          [1]  Only expect it to work with VERY strong signals WAY above the noise floor.
                           
                          [2]  Reduce the RF gain as much as possible consistent with still hearing the signal.
                                What this does is back you off the AGC level-seeking curve, and make any signal
                                present pop way above the noise floor.  Now for AM, this is fine.  For SSB, all
                                you expect is to hear the squelch popping and pumping on voice peaks -- you'll
                                have to manually turn the squelch off, or stop the scan to hear it right.
                           
                            73
                          KW1B
                            NC
                        • radiotech750
                          So if that is true then the radio has a design error? It seems like it to me! If you can t scam at higher rf gain then why would the scan be an option ? Ernie
                          Message 12 of 19 , Sep 18, 2013
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                            So if that is true then the radio has a design error? It seems like it to me! If you can't scam at higher rf gain then why would the scan be an option ?


                            Ernie



                            --- In RADIOSHACKDX394@yahoogroups.com, <radioshackdx394@yahoogroups.com> wrote:

                            The AGC time constants affect scan response. If the attack is very slow and scan speed very fast, the receiver will tune right through without stopping. If release is very slow and scan step very small, it takes many pushes of the start scanning button to get the radio to leave a strong signal behind and get on with scanning. 

                            One of the simpler AGC mods for the DX-394 has the effect of slowing both attack and release time constants, thus having adverse effect on scan operation. While that behaviour has benefit in reducing distortion due to the AGC tracking the modulation, it would be preferable if the AGC was fast for scanning and slow for listening. Motivated by listening rather than scanning issues, I developed AGC mods that, with front panel switches, provided fast attack with three release speeds and AGC on/off. I could manually choose fast release for scanning and slow release for listening. 

                            Until now, I had not thought about the desirability of a mod that would automatically switch to fast AGC when scanning is initiated. It's of little interest to me - just an idea - and I'm not sure there are hooks in the control system that would make feasible such a mod. 

                            Another mod I had explored had the effect of making the S-meter "hotter" which also had some beneficial effect for scanning. It was described at message 2937 http://groups.yahoo.com/group/RADIOSHACKDX394/message/2937

                            Tom ve3meo



                            On 2013-09-14, at 9:55 AM, "William Barrett" <wbarrett@...> wrote:

                             

                            

                            Squelch on an HF receiver works very poorly, too.
                             
                            I will say this: both squelch and scan will work -- sorta -- if you do two things:
                             
                            [1]  Only expect it to work with VERY strong signals WAY above the noise floor.
                             
                            [2]  Reduce the RF gain as much as possible consistent with still hearing the signal.
                                  What this does is back you off the AGC level-seeking curve, and make any signal
                                  present pop way above the noise floor.  Now for AM, this is fine.  For SSB, all
                                  you expect is to hear the squelch popping and pumping on voice peaks -- you'll
                                  have to manually turn the squelch off, or stop the scan to hear it right.
                             
                              73
                            KW1B
                              NC
                          • William Barrett
                            Sales features. Things that get a product sold, that really don t add much of actual use. Get enough of em loaded on, and the damn thing becomes really very
                            Message 13 of 19 , Sep 18, 2013
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                              "Sales features."
                               
                              Things that get a product sold, that really don't add much of actual use.
                               
                              Get enough of 'em loaded on, and the damn thing becomes really very
                              hard to use.
                               
                              Simple is good.
                               
                                73
                              KW1B
                                NC
                               
                              -----Original Message-----
                              From: RADIOSHACKDX394@yahoogroups.com [mailto:RADIOSHACKDX394@yahoogroups.com]On Behalf Of ranger2995@...
                              Sent: Wednesday, September 18, 2013 18:30
                              To: RADIOSHACKDX394@yahoogroups.com
                              Subject: RE: Re: [RADIOSHACKDX394] Re: RE: RE: Scan!

                               

                              So if that is true then the radio has a design error? It seems like it to me! If you can't scam at higher rf gain then why would the scan be an option ?


                              Ernie



                              --- In RADIOSHACKDX394@yahoogroups.com, <radioshackdx394@yahoogroups.com> wrote:

                              The AGC time constants affect scan response. If the attack is very slow and scan speed very fast, the receiver will tune right through without stopping. If release is very slow and scan step very small, it takes many pushes of the start scanning button to get the radio to leave a strong signal behind and get on with scanning. 

                              One of the simpler AGC mods for the DX-394 has the effect of slowing both attack and release time constants, thus having adverse effect on scan operation. While that behaviour has benefit in reducing distortion due to the AGC tracking the modulation, it would be preferable if the AGC was fast for scanning and slow for listening. Motivated by listening rather than scanning issues, I developed AGC mods that, with front panel switches, provided fast attack with three release speeds and AGC on/off. I could manually choose fast release for scanning and slow release for listening. 

                              Until now, I had not thought about the desirability of a mod that would automatically switch to fast AGC when scanning is initiated. It's of little interest to me - just an idea - and I'm not sure there are hooks in the control system that would make feasible such a mod. 

                              Another mod I had explored had the effect of making the S-meter "hotter" which also had some beneficial effect for scanning. It was described at message 2937 http://groups.yahoo.com/group/RADIOSHACKDX394/message/2937

                              Tom ve3meo



                              On 2013-09-14, at 9:55 AM, "William Barrett" <wbarrett@...> wrote:

                               

                              

                              Squelch on an HF receiver works very poorly, too.
                               
                              I will say this: both squelch and scan will work -- sorta -- if you do two things:
                               
                              [1]  Only expect it to work with VERY strong signals WAY above the noise floor.
                               
                              [2]  Reduce the RF gain as much as possible consistent with still hearing the signal.
                                    What this does is back you off the AGC level-seeking curve, and make any signal
                                    present pop way above the noise floor.  Now for AM, this is fine.  For SSB, all
                                    you expect is to hear the squelch popping and pumping on voice peaks -- you'll
                                    have to manually turn the squelch off, or stop the scan to hear it right.
                               
                                73
                              KW1B
                                NC

                            • josephrot
                              Actually, what Tom is describing is simply one of the ways that scan works. Not really a defect in anything, more-so relating how AGC levels. noise, type
                              Message 14 of 19 , Sep 18, 2013
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                                Actually, what Tom is describing is simply one of the ways that "scan" works. Not really a "defect" in anything, more-so relating how AGC levels. noise, type of signal, and so forth can affect scan on receivers that have that option.
                                 
                                For example, scan on the Grundig S750/Tecsun S2000 is defeated purposely on SSB, as it really can't work very well detecting the rise and fall of properly tuned SSB...so, it's defeated when in SSB modes on the Grundig S750/Tecsun S2000.

                                At other times, the S750/Tecsun S2000 scan mode works satisfactorily for its users.

                                That's not saying that anything is "defective" at all, simply an indication of how scan can be a good idea under one set of conditions, but not under another set, etc.

                                So it goes with the DX-394.

                                Joe


                                --- In RADIOSHACKDX394@yahoogroups.com, <radioshackdx394@yahoogroups.com> wrote:

                                
                                "Sales features."
                                 
                                Things that get a product sold, that really don't add much of actual use.
                                 
                                Get enough of 'em loaded on, and the damn thing becomes really very
                                hard to use.
                                 
                                Simple is good.
                                 
                                  73
                                KW1B
                                  NC
                                 
                                -----Original Message-----
                                From: RADIOSHACKDX394@yahoogroups.com [mailto:RADIOSHACKDX394@yahoogroups.com]On Behalf Of ranger2995@...
                                Sent: Wednesday, September 18, 2013 18:30
                                To: RADIOSHACKDX394@yahoogroups.com
                                Subject: RE: Re: [RADIOSHACKDX394] Re: RE: RE: Scan!

                                 

                                So if that is true then the radio has a design error? It seems like it to me! If you can't scam at higher rf gain then why would the scan be an option ?


                                Ernie



                                --- In RADIOSHACKDX394@yahoogroups.com, <radioshackdx394@yahoogroups.com> wrote:

                                The AGC time constants affect scan response. If the attack is very slow and scan speed very fast, the receiver will tune right through without stopping. If release is very slow and scan step very small, it takes many pushes of the start scanning button to get the radio to leave a strong signal behind and get on with scanning. 

                                One of the simpler AGC mods for the DX-394 has the effect of slowing both attack and release time constants, thus having adverse effect on scan operation. While that behaviour has benefit in reducing distortion due to the AGC tracking the modulation, it would be preferable if the AGC was fast for scanning and slow for listening. Motivated by listening rather than scanning issues, I developed AGC mods that, with front panel switches, provided fast attack with three release speeds and AGC on/off. I could manually choose fast release for scanning and slow release for listening. 

                                Until now, I had not thought about the desirability of a mod that would automatically switch to fast AGC when scanning is initiated. It's of little interest to me - just an idea - and I'm not sure there are hooks in the control system that would make feasible such a mod. 

                                Another mod I had explored had the effect of making the S-meter "hotter" which also had some beneficial effect for scanning. It was described at message 2937 http://groups.yahoo.com/group/RADIOSHACKDX394/message/2937

                                Tom ve3meo



                                On 2013-09-14, at 9:55 AM, "William Barrett" <wbarrett@...> wrote:

                                 

                                

                                Squelch on an HF receiver works very poorly, too.
                                 
                                I will say this: both squelch and scan will work -- sorta -- if you do two things:
                                 
                                [1]  Only expect it to work with VERY strong signals WAY above the noise floor.
                                 
                                [2]  Reduce the RF gain as much as possible consistent with still hearing the signal.
                                      What this does is back you off the AGC level-seeking curve, and make any signal
                                      present pop way above the noise floor.  Now for AM, this is fine.  For SSB, all
                                      you expect is to hear the squelch popping and pumping on voice peaks -- you'll
                                      have to manually turn the squelch off, or stop the scan to hear it right.
                                 
                                  73
                                KW1B
                                  NC
                              • Tom Holden
                                Not a design error; rather the RF Gain needs to be set so that interstation noise and interference does not move the S-meter else the scan will stop on it. And
                                Message 15 of 19 , Sep 18, 2013
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                                  Not a design error; rather the RF Gain needs to be set so that interstation noise and interference does not move the S-meter else the scan will stop on it. And a signal must move the S-meter significantly for scan to reliably stop on it. If your receiving conditions and RF Gain settings can be made to satisfy those two conditions, scan works not too badly. Read the Owner’s Manual section on “Search Tuning” on p.16 (curiously, the word “scan” is not used):
                                  “The receiver searches... and tunes to the first frequency it finds with a STRONG signal.” (emphasis mine)
                                  “To tune to stations with weaker signals, use one of the manual tuning methods.” i.e., for scan, the S-meter must be moved significantly, else it skips over weaker signals.
                                  “If the RF GAIN is set fully clockwise, the receiver might not search... Turn the RF GAIN control counterclockwise.” i.e., if the S-meter has a significant reading between stations, scan won’t continue beyond the first step when up or down is pressed.
                                   
                                  Likewise, instructions for the Yaesu FT-817 transceiver:
                                  “Set the SQL/RF knob to the point where background noise is silenced.” i.e., in the absence of signal we don’t want the noise and interference so strong that it opens the squelch and stops scanning. The FT-817 has both squelch and scanning, both of which are triggered by the same signal level but the message is the same as for the DX-394 – you may have to reduce RF Gain depending on receiving conditions so that noise and interference do not stop the scan.
                                   
                                  I just did a little test with my extensively modified DX-394A with just the whip in the basement and have to say that I am quite satisfied that the scan operation behaves as described and intended; I tested on MW and SW. What I was reminded as I refamiliarised myself with the radio was that it was my AGC Defeat mod that had beneficial effect on the scanning discrimination. That mod just disconnects the AGC line from the RF and IF stages but the detector still produces the AGC voltage which continues to drive the meter and scanstop trigger. Because the feedback loop is broken, the AGC voltage swings much more greatly between interstation stuff and stronger signals. Hence scan stops more readily on moderate signals that would be skipped over when the AGC loop is normal. Of course, the volume levels swing much more and very strong signals become very distorted. But as I said before, for listening, I would restore AGC control and slow its release to minimise distortion; for scanning, fast AGC time constants but disconnected from the RF/IF stages for optimum scanning.
                                   
                                  Tom ve3meo
                                   
                                  Sent: Wednesday, September 18, 2013 6:29 PM
                                  Subject: RE: Re: [RADIOSHACKDX394] Re: RE: RE: Scan!
                                   

                                  So if that is true then the radio has a design error? It seems like it to me! If you can't scam at higher rf gain then why would the scan be an option ?

                                   

                                  Ernie

                                • Radionut R
                                  I understand the process of how it works BUT when you have to turn the RF gain down so far that it won t stop on any signals that are less that S( on the meter
                                  Message 16 of 19 , Sep 19, 2013
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                                    I understand the process of how it works BUT when you have to turn the RF gain down so far that it won't stop on any signals that are less that S( on the meter what use is it? To me you should be able to scan at ANY rf gain level.
                                    Thanks for all the info.

                                    Ernie
                                     
                                    Ernie,please trim your posts.
                                     
                                    You did not need allt hose responses in your reply.
                                     
                                    Thank you,The Moderators


                                    On Wed, Sep 18, 2013 at 11:11 PM, <joerotello@...> wrote:

                                    Actually, what Tom is describing is simply one of the ways that "scan" works. Not really a "defect" in anything, more-so relating how AGC levels. noise, type of signal, and so forth can affect scan on receivers that have that option.

                                    For example, scan on the Grundig S750/Tecsun S2000 is defeated purposely on SSB, as it really can't work very well detecting the rise and fall of properly tuned SSB...so, it's defeated when in SSB modes on the Grundig S750/Tecsun S2000.

                                    At other times, the S750/Tecsun S2000 scan mode works satisfactorily for its users.

                                    That's not saying that anything is "defective" at all, simply an indication of how scan can be a good idea under one set of conditions, but not under another set, etc.

                                    So it goes with the DX-394.

                                    Joe



                                    --- In RADIOSHACKDX394@yahoogroups.com, <radioshackdx394@yahoogroups.com> wrote:

                                    "Sales features."
                                    Things that get a product sold, that really don't add much�of actual use.
                                    Get enough of 'em loaded on, and the damn thing becomes really very
                                    hard to use.
                                    Simple is good.
                                    � 73
                                    KW1B
                                    � NC
                                    -----Original Message-----
                                    From: RADIOSHACKDX394@yahoogroups.com [mailto:RADIOSHACKDX394@yahoogroups.com]On Behalf Of ranger2995@...
                                    Sent: Wednesday, September 18, 2013 18:30
                                    To: RADIOSHACKDX394@yahoogroups.com
                                    Subject: RE: Re: [RADIOSHACKDX394] Re: RE: RE: Scan!

                                    So if that is true then the radio has a design error? It seems like it to me! If you can't scam at higher rf gain then why would the scan be an option ?


                                    Ernie



                                    --- In RADIOSHACKDX394@yahoogroups.com, <radioshackdx394@yahoogroups.com> wrote:

                                    The AGC time constants affect scan response. If the attack is very slow and scan speed very fast, the receiver will tune right through without stopping. If release is very slow and scan step very small, it takes many pushes of the start scanning button to get the radio to leave a strong signalbehind and get on with scanning.�

                                    One of the simpler AGC mods for the DX-394 has the effect of slowing both attack and release time constants, thus having adverse effect on scan operation. While that behaviour has benefit in reducing distortion due to the AGC tracking the modulation, it would be preferable if the AGC was fast for scanning and slow for listening. Motivated by listening rather than scanning issues, I developed AGC mods that, with front panel switches, provided fast attack with three release speeds and AGC on/off. I could manually choose fast release for scanning and slow release for listening.�

                                    Until now, I had not thought about the desirability of a mod that would automatically switch to fast AGC when scanning is initiated. It's of little interest to me - just an idea - and I'm not sure there are hooks in the control system that would make feasible such a mod.�

                                    Another mod I had explored had the effect of making the S-meter "hotter" which also had some beneficial effect for scanning. It was described at message 2937�http://groups.yahoo.com/group/RADIOSHACKDX394/message/2937

                                    Tom ve3meo



                                    On 2013-09-14, at 9:55 AM, "William Barrett" <wbarrett@...> wrote:

                                    Squelch on an HF receiver works very poorly, too.
                                    I will say this: both squelch and scan will work -- sorta --�if you do two things:
                                    [1]� Only expect it to work with VERY strong signals WAY above the noise floor.
                                    [2]� Reduce the RF gain as much as possible consistent with still hearing the signal.
                                    ����� What this does is back you off the AGC level-seeking curve, and make any signal
                                    ����� present pop way above the noise floor.� Now for AM, this is fine.� For SSB, all
                                    ����� you expect is to hear the squelch popping and pumping on voice peaks -- you'll
                                    ����� have to manually turn the squelch off, or stop the scan to hear it right.
                                    � 73
                                    KW1B
                                    � NC



                                    --
                                    Remember that when you think you have it all figured out... you wake up to start all over again!
                                    Trust yourself and MOST times you will not be disappointed
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