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Re: [Sangean803] BFO and BFO mods

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  • Mike Westfall, Lost Almost NM
    It is true that adjusting the BFO knob does not adjust the frequency of the BFO itself, which is set to a fixed frequency of 450 kHz. The BFO knob, (only when
    Message 1 of 3 , Mar 20, 2013
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      It is true that adjusting the BFO knob does not adjust the frequency of the
      BFO itself, which is set to a fixed frequency of 450 kHz.
      The BFO knob, (only when the BFO is switched on) tweaks the frequency of
      the 2nd local oscillator, which is set to 55.395 MHz.
      The effect is to move signals up and down in the 450 kHz 2nd IF passband.


      On Wed, Mar 20, 2013 at 3:12 PM, g8voq <hobby_electronics@...>wrote:

      > **
      >
      >
      > Is it true that in the unmodified Sangean 803A, the BFO knob alters the
      > receive frequency - that adjusting the BFO knob does not actually alter the
      > Beat Frequency Oscillator?
      >
      > If this is true, what frequency is the BFO? Thanks.
      >
      > __
      >


      --
      Mike Westfall, Los Alamos, NM
      http://www.facebook.com/mesamike
      My MWDX stuff: http://mesamike.org/radio/mwdx
      Online logbooks: http://dxlogbook.gentoo.net
      Reception Report & QSL Manager for KRSN


      [Non-text portions of this message have been removed]
    • g8voq
      HI. Okay thanks, now lets just examine this. I believe the 450 Khz bandwidths are 2.8 Khz and 6.5 Khz. On SSB we select the 2.8Khz bandwith. When receiving
      Message 2 of 3 , Mar 21, 2013
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        HI. Okay thanks, now lets just examine this.

        I believe the 450 Khz bandwidths are 2.8 Khz and 6.5 Khz.

        On SSB we select the 2.8Khz bandwith.

        When receiving SSB, the injected carrier (BFO) needs to be offset from the centre of the passband. Therefore, it should not be at 450 Khz, but at either side of it, depending on the mode (USB or LSB).

        It appears then, that improvement could be made if an outboard BFO was made to put the carrier injection (BFO frequency) at the proper place with respect to the 450 Khz filter.

        What say? Rich


        --- In Sangean803@yahoogroups.com, "Mike Westfall, Lost Almost NM" <mwdx@...> wrote:
        >
        > It is true that adjusting the BFO knob does not adjust the frequency of the
        > BFO itself, which is set to a fixed frequency of 450 kHz.
        > The BFO knob, (only when the BFO is switched on) tweaks the frequency of
        > the 2nd local oscillator, which is set to 55.395 MHz.
        > The effect is to move signals up and down in the 450 kHz 2nd IF passband.
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