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Re: OK1IF Attenuator Mod. Works Nice.

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  • w9goc
    Jonathan, Vojtech s mod (in the files section) seems to indicate a 470 ohm potentiometer - -why did you go with 500k ? Puzzled, Frederick W9GOC
    Message 1 of 7 , Jan 8, 2009
      Jonathan,

      Vojtech's mod (in the files section) seems to indicate a 470 ohm
      potentiometer - -why did you go with 500k ?

      Puzzled,
      Frederick
      W9GOC
    • Bruce Beford
      ... I believe that was a mis-print. If you looked at the photo of Johnathans rig, you can read the value of the pot. It is a 500 ohm, I believe. -Bruce N1RX
      Message 2 of 7 , Jan 8, 2009
        --- In AT_Sprint@yahoogroups.com, "w9goc" <w9goc@...> wrote:
        >
        > Jonathan,
        >
        > Vojtech's mod (in the files section) seems to indicate a 470 ohm
        > potentiometer - -why did you go with 500k ?
        >
        > Puzzled,
        > Frederick
        > W9GOC
        >

        I believe that was a mis-print. If you looked at the photo of
        Johnathans rig, you can read the value of the pot. It is a 500 ohm, I
        believe.

        -Bruce N1RX
      • J. Haynes
        By the way, that small pot I found at a surplus shop, and could be mailed to anyone who wants to add one to his ATS rig. Contact me off-list. Jonathan 7J1AWL
        Message 3 of 7 , Jan 8, 2009
          By the way, that small pot I found at a surplus shop, and could be mailed to anyone who wants to add one to his ATS rig. Contact me off-list.
          Jonathan 7J1AWL
        • Vojtěch Bubník
          Actually, it is a mod of OK1IF. The pot will make a divider with the 50 Ohm resistor installed on the board. It does not make much difference whether you use a
          Message 4 of 7 , Jan 8, 2009
            Actually, it is a mod of OK1IF.

            The pot will make a divider with the 50 Ohm resistor installed on the board.
            It does not make much difference whether you use a 1k or 270 Ohm pot. The difference between 470 Ohm and 1k is as low as 6dB in maximum attenuation, which is equivalent to 1S. I actually used 1k as I did not find a suitable pot with lower resistance at Mouser. You don't want to go too high with pot resistance, because the attenuator tuning will become too rough at low attenuation levels.

            73, Vojtech OK1IAK

            > ------------ Původní zpráva ------------
            > Od: w9goc <w9goc@...>
            > Předmět: [AT_Sprint] Re: OK1IF Attenuator Mod. Works Nice.
            > Datum: 08.1.2009 18:37:36
            > ----------------------------------------
            > Jonathan,
            >
            > Vojtech's mod (in the files section) seems to indicate a 470 ohm
            > potentiometer - -why did you go with 500k ?
            >
            > Puzzled,
            > Frederick
            > W9GOC
            >
            >
            >
            >
            >
            >
            >
            >
          • radio_kx0r
            ... Vojtech, What improvements does this pot (or front-end attenuator) provide? I imagine it improves the performance of the receiver in the presence of
            Message 5 of 7 , Jan 8, 2009
              --- In AT_Sprint@yahoogroups.com, Vojtìch Bubník <bubnikv@...> wrote:

              Vojtech,

              What improvements does this pot (or front-end attenuator) provide? I
              imagine it improves the performance of the receiver in the presence
              of strong overloading signals.

              I have not had any problem with my ATS-3B rig, probably because I
              mostly use it when the bands aren't very busy. Also I am in
              Colorado, which may reduce the strength of some signals.

              I did find that adding a headphone volume control is a valuable
              improvement for contacts with strong stations. The one I got at
              Radio Shack works fine.

              72/73

              George/Carey
              KX0R

              > Actually, it is a mod of OK1IF.
              >
              > The pot will make a divider with the 50 Ohm resistor installed on
              the board.
              > It does not make much difference whether you use a 1k or 270 Ohm
              pot. The difference between 470 Ohm and 1k is as low as 6dB in
              maximum attenuation, which is equivalent to 1S. I actually used 1k as
              I did not find a suitable pot with lower resistance at Mouser. You
              don't want to go too high with pot resistance, because the attenuator
              tuning will become too rough at low attenuation levels.
              >
              > 73, Vojtech OK1IAK
              >
              > > ------------ Pùvodní zpráva ------------
              > > Od: w9goc <w9goc@...>
              > > Pøedmìt: [AT_Sprint] Re: OK1IF Attenuator Mod. Works Nice.
              > > Datum: 08.1.2009 18:37:36
              > > ----------------------------------------
              > > Jonathan,
              > >
              > > Vojtech's mod (in the files section) seems to indicate a 470 ohm
              > > potentiometer - -why did you go with 500k ?
              > >
              > > Puzzled,
              > > Frederick
              > > W9GOC
              > >
              > >
              > >
              > >
              > >
              > >
              > >
              > >
              >
            • Vojtěch Bubník
              Hi Carey. ... I found out first after I implemented variable bandwidth IF filter. It is less evident with CW filter, but the roughness or ringing that you
              Message 6 of 7 , Jan 9, 2009
                Hi Carey.

                > What improvements does this pot (or front-end attenuator) provide? I
                > imagine it improves the performance of the receiver in the presence
                > of strong overloading signals.

                I found out first after I implemented variable bandwidth IF filter. It is less evident with CW filter, but the roughness or "ringing" that you may sometimes experience is often an effect of:
                - Overloaded front end.
                - Overloaded AVC chip.
                - Clipping on the limiting diodes in AF preamp.
                but less of the IF filter.

                > I have not had any problem with my ATS-3B rig, probably because I
                > mostly use it when the bands aren't very busy. Also I am in
                > Colorado, which may reduce the strength of some signals.

                I am in NJ currently and some signals are extremely strong. I often hear strong signals even with the full attenuation of 26dB (I am using 1k pot, 20 log10(50/1050) is cca. 26dB).

                > I did find that adding a headphone volume control is a valuable
                > improvement for contacts with strong stations. The one I got at
                > Radio Shack works fine.

                The front end attenuator works better, because you attenuate the signal before clipping and distortion, not after. BTW the AVC chip creates quite some distortion if overloaded and if I remember correctly, its control range is about 26dB. With front end attenuator you help the AVC chip a bit. It is probably wise to distribute gain control between the RF attenuator, AVC chip, volume pot and your brain.

                73, Vojtech OK1IAK
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