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Re: [linuxham] RFI and the Computer

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  • Mitchel Baum
    All I can say is that RFI is a problem when all else seems hopeless. I have a MAC-Pro and the weak link there was the MAC Mouse. The USB connections are
    Message 1 of 21 , Apr 30 8:35 AM
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      All I can say is that RFI is a problem when all else seems hopeless. I have a MAC-Pro and the weak link there was the MAC Mouse. The USB connections are subject to points of entry for the little RFI gremlins! If you use a computer in the shack, make sure all of your cables are sheilded and you follow the "single point" grounding scheme.

      I use lots of those little ferrites and a balun on the TX output. Don't forget AC power line either, lots of RF can come back at you from parallel runs of utility power.

      I use two different verticals for HF work, one is the old R5 mounted up about 15 feet and it has its own balun and counterpoise, but it will still radiate RF into the power lines and back into the shack. The other is a ground mounted 4-BTV and it is fed with coax and a large coax type balun at the base (10 turns of RG-8U on a 5 inch PVC form). This antenna requires a set of radials to get any reasonable SWR, but I also added a significant RF ground right at the base (an 8 foot copper plated steel ground rod). This also serves to provide limited lightning protection, but its better than bringing the sparks into the shack without any protection! I live in the lightning belt (Central Florida) and I take lots of care on how to protect the rigs from lightning.

      I use a RigBlaster for digital modes and I bypass the audio lines out of the MAC with 0.01uF caps everywhere. These will not affect the audio, but will serve to remove RF from the lines and drain any RF to ground near where the lines enter or leave any components. For best linearity of your TX signal in digital modes, use a moderately high audio output level and reduce the level right at the TX input. This will help attenuate any RF getting into the modulator. If you are putting audio into a mic input or front panel mic connection, make sure to block the DC component with a capacitor in series with the audio line! Use this method also if you are using the mic input for RX audio to the computer. The mic inputs typically have some small DC to operate the electret microphone elements and this must be removed in order to prevent distortion from the "DC offset".

      Every installation has its unique RF "footprint" especially in the near field of both the antenna and the transmitter. so moving things around only a short distance can "cool" an RF hot spot.

      Mitch Baum / AF2M

    • Roger G6CKR
      ... Also try with the radio switched off you can monitor the SignaLink by the PTT led and the relay clicking. If that is fine then as Ed says go looking for RF
      Message 2 of 21 , May 1, 2010
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        On Thu, 2010-04-29 at 08:03 -0400, Ed wrote:
        > On 04/29/2010 07:56 AM, Jim Glover wrote:
        > > Well, things are not looking good.
        > >
        > > I've downloaded and run a Puppy Linux live CD, and fldigi performs there the
        > > same as it was doing on my openSuSE ... it hangs on transmit. I now have to
        > > suspect that I have a hardware problem. Either my SignaLink USB device, or
        > > my USB interface, must be broken.
        > >
        > > (Does anyone happen to know off the top of their head where on the 'net
        > > SignaLink USB expertise can be found?)
        > >
        > > 73,
        > > Jim WB5UDE
        > >
        >
        > I would suspect some RFI in the shack. Try some chokes on the SL device
        > and see if that helps. Don't overlook the keyboard and/or the mouse.
        >
        > A simple test is to turn the power out to minimum and see what happens.
        >
        > HTH
        >
        > Ed W3NR
        Also try with the radio switched off you can monitor the SignaLink by
        the PTT led and the relay clicking.
        If that is fine then as Ed says go looking for RF issues.

        I discovered the other day that an auto tuner with 3 so239 input sockets
        had a disconnected wire for the common ground of the 3 sockets and the
        circuit board.
        It did not stop the tuner matching but was causing rfi.
        73 Roger G6CKR
      • Roger G6CKR
        ... The perils of playing catchup on a busy list. pleased to see you have nailed the reason at least and ;ets hope the fix is easy.. Probably worth having the
        Message 3 of 21 , May 1, 2010
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          On Thu, 2010-04-29 at 18:13 -0700, Jim Glover wrote:
          > On Thu, Apr 29, 2010 at 08:03:49AM -0400, Ed wrote:
          > > On 04/29/2010 07:56 AM, Jim Glover wrote:
          > > > Well, things are not looking good.
          > > >
          > > > I've downloaded and run a Puppy Linux live CD, and fldigi performs there the
          > > > same as it was doing on my openSuSE ... it hangs on transmit. I now have to
          > > > suspect that I have a hardware problem. Either my SignaLink USB device, or
          > > > my USB interface, must be broken.
          > > >
          > > > (Does anyone happen to know off the top of their head where on the 'net
          > > > SignaLink USB expertise can be found?)
          > > >
          > > > 73,
          > > > Jim WB5UDE
          > > >
          > >
          > > I would suspect some RFI in the shack. Try some chokes on the SL device
          > > and see if that helps. Don't overlook the keyboard and/or the mouse.
          > >
          > > A simple test is to turn the power out to minimum and see what happens.
          > >
          > > HTH
          > >
          > > Ed W3NR
          >
          > Ed, you pegged it.
          >
          > Even turning the power down to 5 watts did not solve the problem. I had
          > to tune it out of band so it would refuse to transmit, to confirm that the
          > only difference between joy, and no joy, was whether it was transmitting.
          >
          > Now I'm going to be looking for some of those snap-together cores to wind
          > a few turns of my USB cable, for starters, around.
          >
          > 73,
          > Jim WB5UDE
          >
          The perils of playing catchup on a busy list.
          pleased to see you have nailed the reason at least and ;ets hope the fix
          is easy..
          Probably worth having the other post in the archive as it is a bit
          easier that forcing the radio out of band.
          My opened TS570 would have to go a long way before it would not TX.
          73 Roger G6cKR
        • Jim Glover
          ... I made that choice due to the fact that otherwise, I still would not be able to rule out the possibility that the SignaLink USB device might have been
          Message 4 of 21 , May 1, 2010
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            > Probably worth having the other post in the archive as it is a bit
            > easier that forcing the radio out of band.

            I made that choice due to the fact that otherwise, I still would not
            be able to rule out the possibility that the SignaLink USB device
            might have been behaving differently with a connection to the XCVR,
            vs. none. My test led me to an even higher confidence that there
            was no room for error--it was unquestionably RFI. Nevertheless, I
            agree that your alternative is easier (and for some of us, would be
            dramatically easier).

            Thanks, Roger!

            On Sat, May 01, 2010 at 11:15:34AM +0100, Roger G6CKR wrote:
            > On Thu, 2010-04-29 at 18:13 -0700, Jim Glover wrote:
            > > On Thu, Apr 29, 2010 at 08:03:49AM -0400, Ed wrote:
            > > > On 04/29/2010 07:56 AM, Jim Glover wrote:
            > > > > Well, things are not looking good.
            > > > >
            > > > > I've downloaded and run a Puppy Linux live CD, and fldigi performs there the
            > > > > same as it was doing on my openSuSE ... it hangs on transmit. I now have to
            > > > > suspect that I have a hardware problem. Either my SignaLink USB device, or
            > > > > my USB interface, must be broken.
            > > > >
            > > > > (Does anyone happen to know off the top of their head where on the 'net
            > > > > SignaLink USB expertise can be found?)
            > > > >
            > > > > 73,
            > > > > Jim WB5UDE
            > > > >
            > > >
            > > > I would suspect some RFI in the shack. Try some chokes on the SL device
            > > > and see if that helps. Don't overlook the keyboard and/or the mouse.
            > > >
            > > > A simple test is to turn the power out to minimum and see what happens.
            > > >
            > > > HTH
            > > >
            > > > Ed W3NR
            > >
            > > Ed, you pegged it.
            > >
            > > Even turning the power down to 5 watts did not solve the problem. I had
            > > to tune it out of band so it would refuse to transmit, to confirm that the
            > > only difference between joy, and no joy, was whether it was transmitting.
            > >
            > > Now I'm going to be looking for some of those snap-together cores to wind
            > > a few turns of my USB cable, for starters, around.
            > >
            > > 73,
            > > Jim WB5UDE
            > >
            > The perils of playing catchup on a busy list.
            > pleased to see you have nailed the reason at least and ;ets hope the fix
            > is easy..
            > Probably worth having the other post in the archive as it is a bit
            > easier that forcing the radio out of band.
            > My opened TS570 would have to go a long way before it would not TX.
            > 73 Roger G6cKR
            >
          • Hylton Conacher (ZR1HPC)
            ... By now I hope they are looking better :) ... You might try the following group: http://groups.yahoo.com/group/TigertronicsSignaLink/ 73 de ZR1HPC
            Message 5 of 21 , May 1, 2010
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              Jim Glover wrote:
              > Well, things are not looking good.

              By now I hope they are looking better :)

              <snip>

              > (Does anyone happen to know off the top of their head where on the 'net
              > SignaLink USB expertise can be found?)

              You might try the following group:
              http://groups.yahoo.com/group/TigertronicsSignaLink/

              73 de ZR1HPC
              Hylton
              --
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