Loading ...
Sorry, an error occurred while loading the content.

Re: T2-301 jamming FM broadcast

Expand Messages
  • ac2ev
    I think you ve hit on something there.
    Message 1 of 13 , May 26, 2011
    • 0 Attachment
      I think you've hit on something there.

      --- In tracker2@yahoogroups.com, ve3id <ve3id@...> wrote:
      >
      > It could be that the deviation is set too high on the tracker and
      > causing mixing products.. I have the same problem with a T2 hooked up
      > to a 5W Kenwood HT, and I checked the HT before putting it in the car on
      > a spectrum analyser with no problems seen - but adding the external
      > modulation from the T2 causes it to wipe out my FM radio, also 2m and
      > 220 and 440 on some freqs.
      >
      > Thanks to the one who suggested power-line conducted RF, I will have to
      > check for that this weekend!
      >
      > 73
      > ve3id
      >
      >
      > On 11-05-25 09:30, ac2ev wrote:
      > >
      > > I have to disagree.
      > >
      > > 1. It affects the car's radio in the parking spot next to me.
      > > 2. I can hold a HT up against my side window (where the FM receiving
      > > antenna is) and key it and not affect the FM Radio one bit.
      > >
      > > I think the Friendcom radio is bad.
      > >
      > > --- In tracker2@yahoogroups.com <mailto:tracker2%40yahoogroups.com>,
      > > James Ewen <ve6srv@> wrote:
      > > >
      > > > On Wed, May 25, 2011 at 5:30 AM, Don <ac2ev@> wrote:
      > > >
      > > > > My Tracker is effectively jamming FM broadcast while it transmitting.
      > > >
      > > > This is called front end overload. Move your tracker antenna away from
      > > > the broadcast antenna, or reduce the output power from the tracker to
      > > > help alleviate the issue.
      > > >
      > > > James
      > > > VE6SRV
      > > >
      > >
      > >
      >
    • Matt Cook
      Hi, It sounds like you need to put a bandpass filter on the output of the 2m transmitter to reject strong out of band signals. If you are experiencing mixing
      Message 2 of 13 , May 26, 2011
      • 0 Attachment
        Hi,

        It sounds like you need to put a bandpass filter on the output of the 2m transmitter to reject strong out of band signals.

        If you are experiencing mixing products landing on the FM broadcast band when (and only when) the APRS radio transmits then there is a out of band signal mixing in your final PA transistor which is then being re-radiated locally.

        This problem occurs quite frequently in co-sited VHF/UHF repeater systems.   I have even seen the 5.0MHz WWV time-signal lockup a local amateur UHF repeater with a 5MHz split (negative offset).  WWV was getting into the PA transistor and mixing up into the receiver holding the squelch open until the repeater timed out.  Easy to identify quite difficult to kill.

        If you can identify which local transmitter is getting into the 2m output then a simple coaxial notch filter (tee-piece and 1/4 wave open circuit coax) is usually sufficient to knock it out.  Otherwise a RF bandpass filter is required which can be a little more tricky.

        Don't forget that the local signal can be below or above the APRS channel, the sum and the difference between these signals will be somewhere within the FM broadcast band.  At a guess I'd be looking at the local TV stations first, since these are 7-10MHz wide usually.

        Hope that this helps.

        73's

        Matthew
        VK5ZM

        On Wed, May 25, 2011 at 9:00 PM, Don <ac2ev@...> wrote:
         

        I CC Scott on this issue just wanting to see if anyone else has experienced it.

        My Tracker is effectively jamming FM broadcast while it transmitting. This happens for all but the absolute strongest FM broadcasts. I cross-verified this against a battery operated handheld radio and it jams both.

        I get a loud static carrier on FM which effectively jams the broadcast and knocks out the stereo light. This happens on low,medium power broadcasts. There's a local 50KW station that it can't knock out.

        I'm using the magmount from Argent Data and it's connected to my Garmin through a shielded serial cable and power is via the Argent serial+power no extra length.

        It's connected to the aux power port in the back of my Honda Odyssey Van.

        Again this happens with the car's radio and a battery operated portable.


      • Fred Hillhouse
        The tracker radio is messing with the FM receiver, not the FM transmitter messing with the tracker radio. So while a band pass filter on the tracker radio is
        Message 3 of 13 , May 27, 2011
        • 0 Attachment
          The tracker radio is messing with the FM receiver, not the FM transmitter messing with the tracker radio. So while a band pass filter on the tracker radio is good, it probably won't solve the problem. I have this happening as well with my JVC unit. It didn't happen with the Toyota unit but I just don't care. I rather have APRS than AM/FM and I mostly listen to my own music anyway commercial free. :)
           
          Best regards,
          Fred, N7FMH
           


          From: tracker2@yahoogroups.com [mailto:tracker2@yahoogroups.com] On Behalf Of Matt Cook
          Sent: Thursday, May 26, 2011 19:45
          To: tracker2@yahoogroups.com
          Subject: Re: [tracker2] T2-301 jamming FM broadcast

           

          Hi,

          It sounds like you need to put a bandpass filter on the output of the 2m transmitter to reject strong out of band signals.

          If you are experiencing mixing products landing on the FM broadcast band when (and only when) the APRS radio transmits then there is a out of band signal mixing in your final PA transistor which is then being re-radiated locally.

          This problem occurs quite frequently in co-sited VHF/UHF repeater systems.   I have even seen the 5.0MHz WWV time-signal lockup a local amateur UHF repeater with a 5MHz split (negative offset).  WWV was getting into the PA transistor and mixing up into the receiver holding the squelch open until the repeater timed out.  Easy to identify quite difficult to kill.

          If you can identify which local transmitter is getting into the 2m output then a simple coaxial notch filter (tee-piece and 1/4 wave open circuit coax) is usually sufficient to knock it out.  Otherwise a RF bandpass filter is required which can be a little more tricky.

          Don't forget that the local signal can be below or above the APRS channel, the sum and the difference between these signals will be somewhere within the FM broadcast band.  At a guess I'd be looking at the local TV stations first, since these are 7-10MHz wide usually.

          Hope that this helps.

          73's

          Matthew
          VK5ZM

          On Wed, May 25, 2011 at 9:00 PM, Don <ac2ev@...> wrote:
           

          I CC Scott on this issue just wanting to see if anyone else has experienced it.

          My Tracker is effectively jamming FM broadcast while it transmitting. This happens for all but the absolute strongest FM broadcasts. I cross-verified this against a battery operated handheld radio and it jams both.

          I get a loud static carrier on FM which effectively jams the broadcast and knocks out the stereo light. This happens on low,medium power broadcasts. There's a local 50KW station that it can't knock out.

          I'm using the magmount from Argent Data and it's connected to my Garmin through a shielded serial cable and power is via the Argent serial+power no extra length.

          It's connected to the aux power port in the back of my Honda Odyssey Van.

          Again this happens with the car's radio and a battery operated portable.


        Your message has been successfully submitted and would be delivered to recipients shortly.