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Re: [perseus_SDR] 100Hz QRN [1 Attachment]

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  • Leif Asbrink
    Hello Andrew, ... This is a pulse train with a precise repetition frequency. I think we can remove this kind of interference in software and I would be very
    Message 1 of 7 , Feb 28, 2012
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      Hello Andrew,

      > I've been trying to identify the cause of annoying QRN that has appeared
      > since Christmas. It affects a wide range of frequencies and a typical
      > example is attached, centred on 7488kHz.
      This is a pulse train with a precise repetition frequency.
      I think we can remove this kind of interference in software and
      I would be very interested in recordings from your QTH in case
      you find that it is not caused by RF stage AM modulation.

      > The interference is in very discrete bands, separated by 99-100Hz, very
      > clearly defined. I have heard the interference on an AOR 7030 with the
      > Perseus and associated computer turned off, which I think eliminates the
      > Perseus, laptop and their power supplies. In my experience power supply
      > noise is generally "noisy" not the very linear bands you can see in the
      > attachment.
      Agree. The 100 Hz lines are phase stable. I have actually not seen
      something like this before.


      > The interference often appears on Perseus to be centred on broadcast
      > stations, with the strength of the interference bands reducing to either
      > side of the carrier frequency. In the attachment is an example centred on
      > 7480kHz made at the same time.
      Hmmm, that might suggest some error on your supply
      voltage. In case you see the N*100Hz carriers symmetrically
      around strong carriers I would expect you have an RF amplifier that
      has an inadequate DC supply providing 100 Hz AM modulation in the
      form of short pulses. (Of too low supply voltage.)

      73

      Leif / SM5BSZ
    • Andrew Brade
      I ve been trying to identify the cause of annoying QRN that has appeared since Christmas. It affects a wide range of frequencies and a typical example is
      Message 2 of 7 , Feb 28, 2012
      • 1 Attachment
      • 1.3 MB

      I’ve been trying to identify the cause of annoying QRN that has appeared since Christmas. It affects a wide range of frequencies and a typical example is attached, centred on 7488kHz.

       

      The interference is in very discrete bands, separated by 99-100Hz, very clearly defined. I have heard the interference on an AOR 7030 with the Perseus and associated computer turned off, which I think eliminates the Perseus, laptop and their power supplies. In my experience power supply noise is generally “noisy” not the very linear bands you can see in the attachment.

       

      The interference often appears on Perseus to be centred on broadcast stations, with the strength of the interference bands reducing to either side of the carrier frequency. In the attachment is an example centred on 7480kHz made at the same time.

       

      It’s not particularly audible on a portable receiver as I think with only an internal aerial the sensitivity is not good enough.

       

      Has anyone ever seen anything like it? Any clues as to where to look for the source?

       

      All help gratefully received.

       

      73

       

      Andrew Brade

      East Yorkshire

      England

    • andrew138712
      Thanks Leif - I will mail you off-list for a further discussion, but I rather thought along the same lines. It is just too regular to be something from a
      Message 3 of 7 , Feb 28, 2012
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        Thanks Leif - I will mail you off-list for a further discussion, but I rather thought along the same lines. It is just too regular to be something from a domestic appliance and the centring on broadcast frequencies is too much of a coincidence.

        If others are interested I will report back any findings to this list.

        73

        Andrew
        --- In perseus_SDR@yahoogroups.com, Leif Asbrink <leif@...> wrote:
        >
        > Hello Andrew,
        >
        > > I've been trying to identify the cause of annoying QRN that has appeared
        > > since Christmas. It affects a wide range of frequencies and a typical
        > > example is attached, centred on 7488kHz.
        > This is a pulse train with a precise repetition frequency.
        > I think we can remove this kind of interference in software and
        > I would be very interested in recordings from your QTH in case
        > you find that it is not caused by RF stage AM modulation.
        >
        > > The interference is in very discrete bands, separated by 99-100Hz, very
        > > clearly defined. I have heard the interference on an AOR 7030 with the
        > > Perseus and associated computer turned off, which I think eliminates the
        > > Perseus, laptop and their power supplies. In my experience power supply
        > > noise is generally "noisy" not the very linear bands you can see in the
        > > attachment.
        > Agree. The 100 Hz lines are phase stable. I have actually not seen
        > something like this before.
        >
        >
        > > The interference often appears on Perseus to be centred on broadcast
        > > stations, with the strength of the interference bands reducing to either
        > > side of the carrier frequency. In the attachment is an example centred on
        > > 7480kHz made at the same time.
        > Hmmm, that might suggest some error on your supply
        > voltage. In case you see the N*100Hz carriers symmetrically
        > around strong carriers I would expect you have an RF amplifier that
        > has an inadequate DC supply providing 100 Hz AM modulation in the
        > form of short pulses. (Of too low supply voltage.)
        >
        > 73
        >
        > Leif / SM5BSZ
        >
      • Jay Bromley
        Hi Andrew Yes, a battery charger for a kid s scooter. Mainly from 40m and up, it was horrible. It was fairly far away from my house and was coupled into the
        Message 4 of 7 , Feb 28, 2012
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          Hi Andrew

           

          Yes, a battery charger for a kid’s scooter.  Mainly from 40m and up, it was horrible.  It was fairly far away from my house and was coupled into the power grid making it much worse.  It was like a giant spark gap transmitter.  The unit was damaged and had failed into a weird mode not hooked up to a battery.  It had a small LED that would fire off every second or two.  It took several days to find it and then once narrowed down to the house took another day going from room to room.  Finally found it hidden behind a box in the garage.  The owner of the house thought I was come crazy ham making thing worse to trouble shoot, but once I identified the failed unit they were very glad it didn’t burn the house down! 

           

          I have heard that electric blankets, small beer refrigerators, pumps for pools, anything with a poorly design switching power supply can do the same thing.    

           

          In the USA, the ARRL was a big help with the above.  73 de w5jay/jay..

           

           

          [Attachment(s) from Andrew Brade included below]


          I’ve been trying to identify the cause of annoying QRN that has appeared since Christmas. It affects a wide range of frequencies and a typical example is attached, centred on 7488kHz.

           

          The interference is in very discrete bands, separated by 99-100Hz, very clearly defined. I have heard the interference on an AOR 7030 with the Perseus and associated computer turned off, which I think eliminates the Perseus, laptop and their power supplies. In my experience power supply noise is generally “noisy” not the very linear bands you can see in the attachment.

           

          The interference often appears on Perseus to be centred on broadcast stations, with the strength of the interference bands reducing to either side of the carrier frequency. In the attachment is an example centred on 7480kHz made at the same time.

           

          It’s not particularly audible on a portable receiver as I think with only an internal aerial the sensitivity is not good enough.

           

          Has anyone ever seen anything like it? Any clues as to where to look for the source?

           

          All help gratefully received.

           

          73

           

          Andrew Brade

          East Yorkshire

          England

           

          Attachment(s) from Andrew Brade

          1 of 1 File(s)



        • Werner Karn
          Andrew, I could think of a defect AM shortwave transmitter, showing 100Hz and harmonics unsufficiently suppressed. I have seen this before on a saudi arabien
          Message 5 of 7 , Feb 29, 2012
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            Andrew,
             
            I could think of a defect AM shortwave transmitter, showing 100Hz and harmonics unsufficiently suppressed.
            I have seen this before on a saudi arabien transmitter with a 60Hz/120Hz plus harmonics " modulation ".
             
            73,
             
            Werner

            2012/2/28 Andrew Brade <andrew.brade@...>
             
            [Attachment(s) from Andrew Brade included below]

            I’ve been trying to identify the cause of annoying QRN that has appeared since Christmas. It affects a wide range of frequencies and a typical example is attached, centred on 7488kHz.

             

            The interference is in very discrete bands, separated by 99-100Hz, very clearly defined. I have heard the interference on an AOR 7030 with the Perseus and associated computer turned off, which I think eliminates the Perseus, laptop and their power supplies. In my experience power supply noise is generally “noisy” not the very linear bands you can see in the attachment.

             

            The interference often appears on Perseus to be centred on broadcast stations, with the strength of the interference bands reducing to either side of the carrier frequency. In the attachment is an example centred on 7480kHz made at the same time.

             

            It’s not particularly audible on a portable receiver as I think with only an internal aerial the sensitivity is not good enough.

             

            Has anyone ever seen anything like it? Any clues as to where to look for the source?

             

            All help gratefully received.

             

            73

             

            Andrew Brade

            East Yorkshire

            England


          • Jack Weber
            Hi Andrew, 100 Hz pulses still make me suspect it s something related to your 50 Hz mains power. I think I suggested before that it may be smart metering or
            Message 6 of 7 , Feb 29, 2012
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              Hi Andrew,

              100 Hz pulses still make me suspect it's something related to your 50 Hz mains power. I think I suggested before that it may be smart metering or other switching signals on the mains. If it's not that, it occurs to me that many home automation devices - for switching lights on and off, opening and closing curtains remotely, and so on - communicate by using pulses that are injected into the mains and synchronised to the zero crossings. Of which there are, of course, 100 per second.

              Maybe one of your neighbours has installed something like that. If so, and it's getting through to the DC power in your receiver, it could be modulating the received signals to produce those sidebands. If you are able to run either your AR7030 or the Perseus with its associated laptop from a battery, that should indicate whether it's coming in through the mains or through the antenna, which at least narrows down the possibilities.

              If, as it appears, this is the result of a 100Hz signal modulating received carriers, then it's either entering the DC power line of the receiver or it's occurring in your antenna or feeder, probably in a poor joint that has become semiconducting. Have you tried using an alternative antenna - just a simple length of outdoor wire connected directly to the receiver - to see if the same problem occurs?

              Best regards,

              Jack


              On 28 Feb 2012, at 20:57, Andrew Brade wrote:

               

              I’ve been trying to identify the cause of annoying QRN that has appeared since Christmas. It affects a wide range of frequencies and a typical example is attached, centred on 7488kHz.

               

              The interference is in very discrete bands, separated by 99-100Hz, very clearly defined. I have heard the interference on an AOR 7030 with the Perseus and associated computer turned off, which I think eliminates the Perseus, laptop and their power supplies. In my experience power supply noise is generally “noisy” not the very linear bands you can see in the attachment.

               

              The interference often appears on Perseus to be centred on broadcast stations, with the strength of the interference bands reducing to either side of the carrier frequency. In the attachment is an example centred on 7480kHz made at the same time.

               

              It’s not particularly audible on a portable receiver as I think with only an internal aerial the sensitivity is not good enough.

               

              Has anyone ever seen anything like it? Any clues as to where to look for the source?

               

              All help gratefully received.

               

              73

               

              Andrew Brade

              East Yorkshire

              England



            • andrew138712
              Thanks to all who contributed to this. I worked out that it was not the Perseus or the laptop by hearing the same QRN on my AOR with all power to the laptop
              Message 7 of 7 , Feb 29, 2012
              • 0 Attachment
                Thanks to all who contributed to this.

                I worked out that it was not the Perseus or the laptop by hearing the same QRN on my AOR with all power to the laptop and Perseus isolated.

                I strongly suspected that it was something induced in the equipment rather than something the antennas were picking up. A portable receiver on batteries did not pick up the noise.

                Leif Asbrink suggested it was a problem with the DC supply to an RF amplifier (along the same lines as Jack below). A process of using various receivers and antennas led me to suspect that it is something to do with the antenna controller - a Wellbrook phased array which contains RF amplifiers (three in total). All three are supplied from a plug-in power supply which actually is a regulated transformer/rectifier rather than a switch-mode type, rated at 12V and 800mA.

                When this power supply was disconnected the signal strength dropped by about 60dB because of the loss of amplification, but the interference bands disappeared. I took a voltmeter to the power supply and it measured 19.99V d.c. and 46V a.c.! Not having an oscillosope I don't know what the a.c. frequency was but I would expect 100Hz which is the resultant ripple from full-wave rectification.

                Today I bought a new power supply and the problem has disappeared!

                I should say that the problem is nothing to do with Wellbrook - they don't supply the PSU, I bought it about four years ago and it has evidently failed in the last couple of months. To its credit, the Wellbrook equipment continues to work despite being exposed to voltages beyond the design figures.

                So thanks to Leif and all who guided me to the solution.

                73

                Andrew

                --- In perseus_SDR@yahoogroups.com, Jack Weber <cloudscan@...> wrote:
                >
                > Hi Andrew,
                >
                > 100 Hz pulses still make me suspect it's something related to your 50 Hz mains power. I think I suggested before that it may be smart metering or other switching signals on the mains. If it's not that, it occurs to me that many home automation devices - for switching lights on and off, opening and closing curtains remotely, and so on - communicate by using pulses that are injected into the mains and synchronised to the zero crossings. Of which there are, of course, 100 per second.
                >
                > Maybe one of your neighbours has installed something like that. If so, and it's getting through to the DC power in your receiver, it could be modulating the received signals to produce those sidebands. If you are able to run either your AR7030 or the Perseus with its associated laptop from a battery, that should indicate whether it's coming in through the mains or through the antenna, which at least narrows down the possibilities.
                >
                > If, as it appears, this is the result of a 100Hz signal modulating received carriers, then it's either entering the DC power line of the receiver or it's occurring in your antenna or feeder, probably in a poor joint that has become semiconducting. Have you tried using an alternative antenna - just a simple length of outdoor wire connected directly to the receiver - to see if the same problem occurs?
                >
                > Best regards,
                >
                > Jack
                >
                >
                > On 28 Feb 2012, at 20:57, Andrew Brade wrote:
                >
                > > [Attachment(s) from Andrew Brade included below]
                > >
                > > I've been trying to identify the cause of annoying QRN that has appeared since Christmas. It affects a wide range of frequencies and a typical example is attached, centred on 7488kHz.
                > >
                > >
                > >
                > > The interference is in very discrete bands, separated by 99-100Hz, very clearly defined. I have heard the interference on an AOR 7030 with the Perseus and associated computer turned off, which I think eliminates the Perseus, laptop and their power supplies. In my experience power supply noise is generally "noisy" not the very linear bands you can see in the attachment.
                > >
                > >
                > >
                > > The interference often appears on Perseus to be centred on broadcast stations, with the strength of the interference bands reducing to either side of the carrier frequency. In the attachment is an example centred on 7480kHz made at the same time.
                > >
                > >
                > >
                > > It's not particularly audible on a portable receiver as I think with only an internal aerial the sensitivity is not good enough.
                > >
                > >
                > >
                > > Has anyone ever seen anything like it? Any clues as to where to look for the source?
                > >
                > >
                > >
                > > All help gratefully received.
                > >
                > >
                > >
                > > 73
                > >
                > >
                > >
                > > Andrew Brade
                > >
                > > East Yorkshire
                > >
                > > England
                > >
                > >
                > >
                >
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