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Re: [AT_Sprint] MTR receiver offset

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  • Steven Weber
    No, you should not have to use RIT all the time. You probably don t have the BFO trimmer set quite right. Steve KD1JV
    Message 1 of 5 , Dec 7, 2012
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      No, you should not have to use RIT all the time. You probably don't have the
      BFO trimmer set quite right.

      Steve KD1JV


      > Thanks to this group, a previously-built MTR is now in my eager hands and
      > has provided several excellent contacts.
      >
      > However, it is necessary to use the RIT function to hear the other station
      > clearly as the offset between transmit and receive appears off.
      >
      >
      > Thank you,
      > Don, K3RLL
    • radio_kx0r
      Don, Steve is right about the BFO adjustment. What you really should do is to go to the part of the manual on P13 (for the 4-20-2012 manual version) -
      Message 2 of 5 , Dec 7, 2012
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        Don,

        Steve is right about the BFO adjustment.

        What you really should do is to go to the part of the manual on P13 (for the 4-20-2012 manual version) - available in KD1JV's FILES here on this website. This is Local Oscillator frequency trim and BFO adjustment. If I were you I would go through the whole thing. Steve's procedure is concise and will give you a precise alignment, provided you do just what it says.

        Consider borrowing a scope or taking the rig to someone who has a scope, and follow the procedure. The numbered steps are all important for setting up the BFO so the desired signal is centered in the crystal filter passband, accurately lined up with the transmit signal, and so the beat tone you hear is centered in the selective audio filter.

        When you tune across the filter passband, counting the steps like Steve says, be sure you go all the way across to each side while watching the signal amplitude, so you find where the crystal filter falls off rapidly at both edges of the passband. There may be small variations within the passband, but what you want to find is the the full width of the filter's passband, and then set the signal in the center of that, by counting the total steps divided by 2 like Steve says - not at the actual peak of the filter!

        Since the BFO is a bit off, you would be smart to check the other adjustments on pages 12 and 13. The reference oscillator calibration may not be required, and doing it requires some equipment like a counter and/or test oscillator - usually the reference oscillators on these rigs are pretty close to start with - but if someone tried to do the cal and did it wrong, the cal could be off enough to matter.

        If you want to cheat, just adjust the BFO trimmer so the receive signal lines up with the transmit signal with the RIT off. You can do this using another rig, provided its receive and transmit frequencies are lined up accurately also. Be sure to transmit both rigs into dummy load(s), not into each other! Carefully avoid excess signal into either rig's receiver!! This way you can avoid using the RIT on most signals.

        However, just because the receive and transmit signals agree in your MTR doesn't tell if the rest of the alignment is right.

        The receiver input filter peaking on page 13 is worth checking, because the peak on one of the trimmers for each band is really sharp and must be set carefully. Maybe the builder didn't get it quite right also. Ideally you should do this using a signal generator, but you can peak it with an antenna or other signal input. You need to make certain that whatever you connect to the MTR antenna jack is close to 50 ohms resistive before you adjust the trimmers. If you peak the trimmers with an antenna that is not exactly 50 ohms, the trimmers will be off. The easiest way to be sure is to use an RF attenuator on the antenna input - at least 10 db - that way the input of the MTR will see about 50 ohms for the adjustment. If you have enough noise coming in, you can peak on the noise if you can hear the peak. If you peak on a signal, use a signal that isn't varying in strength. Do this adjustment for each band near the frequency you plan to use.

        This is a very nice receiver once you have it adjusted!

        72/73
        KX0R



        --- In AT_Sprint@yahoogroups.com, "k3rll" <McBride_D@...> wrote:
        >
        > Thanks to this group, a previously-built MTR is now in my eager hands and has provided several excellent contacts.
        >
        > However, it is necessary to use the RIT function to hear the other station clearly as the offset between transmit and receive appears off.
        >
        > I've looked through the assembly manual online and ..., well that's why I'm seeking the collective wisdom of this group.
        > Without test equipment and with 68-year old shaky hands, how does one adjust the receiver offset to center the received signal in the passband permanently, so to speak, e.g., without using RIT each time?
        >
        > Thank you,
        > Don, K3RLL
        >
      • richardk4krw
        Regarding the BFO alignment and a scope If you don t have access to a scope, I ve made these kinds of adjustments monitoring the audio output of the rig using
        Message 3 of 5 , Dec 8, 2012
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          Regarding the BFO alignment and a scope

          If you don't have access to a scope, I've made these kinds of adjustments monitoring the audio output of the rig using digital modes software. So, if you have a computer, a digital modes interface (something like a Rigblaster or Signalink) and the software (DM780 would be one), you would be surprised at how helpful they can be. I used this setup when aligning my Wilderness Sierra rig and it really worked well.

          In my case, my previous alignment made it such that narrowing the crystal filter on my Sierra made signals disappear (it wasn't centered).

          The waterfall display really helped when adjusting the BFO because I could literally see the passband.

          On 40 meters with no antenna connected, the ambient noise worked well as a 'semi' white noise source.

          So, if you have the equipment, this is something else you can try. It has worked great for me.
        • richardk4krw
          One more note: Actually, in my case I didn t even use a sound card interface. I just ran the earphone output straight into the sound card microphone jack. It
          Message 4 of 5 , Dec 8, 2012
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            One more note:

            Actually, in my case I didn't even use a sound card interface. I just ran the earphone output straight into the sound card microphone jack. It worked great. (Sorry cobwebs).

            Richard - K4KRW

            --- In AT_Sprint@yahoogroups.com, "richardk4krw" <r_in_remac@...> wrote:
            >
            > Regarding the BFO alignment and a scope
            >
            > If you don't have access to a scope, I've made these kinds of adjustments monitoring the audio output of the rig using digital modes software. So, if you have a computer, a digital modes interface (something like a Rigblaster or Signalink) and the software (DM780 would be one), you would be surprised at how helpful they can be. I used this setup when aligning my Wilderness Sierra rig and it really worked well.
            >
            > In my case, my previous alignment made it such that narrowing the crystal filter on my Sierra made signals disappear (it wasn't centered).
            >
            > The waterfall display really helped when adjusting the BFO because I could literally see the passband.
            >
            > On 40 meters with no antenna connected, the ambient noise worked well as a 'semi' white noise source.
            >
            > So, if you have the equipment, this is something else you can try. It has worked great for me.
            >
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