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Denon UD-M31 tuner module

Discussion in 'Electronic Repair' started by Thomas Tornblom, Aug 25, 2006.

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  1. My kids have a Denon UD-M30 and UD-M31 micro receiver/cd-player combo,
    which works great, except for one thing, the tuners are too wide band.

    We have a local FM station on 106.5 MHz, transmitting with 4 kW, and
    we're trying to tune into a station transmitting with 1 kW at 106.3
    MHz in Stockholm, which is about 80 km from here.

    I have stacked two giant FM antennas with a proper stacking filter,
    directed at the Stockholm transmitter, and I have great reception on
    weak stations way farther away. We also have great reception of a 1 kW
    transmitter at 104.7, transmitting from the same location as the one
    we're interested in.

    Using an old antenna instrument I can see that I have more than a 30
    dB difference in signal strength between the 106.3 and 106.5 signals.

    I have three receivers which receives 106.3 with fair to good quality,
    a Denon AVR-3805, an old digitally tuned Kenwood receiver, and an old
    analog tuner. I have also tried an old digitally tuned Pioneer car
    stereo, which had absolutely no problems receiving 106.3 from the
    antenna wiring in my house.

    The small Denons have big problems though, and I believe the problem
    is that the IF bandwidth of the filters in the tuners are too wide and
    they can't detect the weak 106.3 from the strong 106.5.

    I have seen a few sites on the net recommending changing the ceramic
    filters to something narrower, and that seems like a reasonable and
    fairly simple change.

    Is there anyone who have experience and/or schematics for these
    tuners? I looked into one of them, and the tuner appears to be a
    separate small module, which I didn't open as it seemed like a bit
    more work than I was prepared to set aside today.

    What bandwidth and how many are the stock filters? I assume something
    on the order of 280 kHz, and I'm contemplating replacing some of them
    with 180 kHz filters.

    Oh, and they both have RDS, which I believe may need slightly more bw
    to work reliably.
  2. You could try Googling the tuner info page - theres DX tweaks over could probably contact them for advice.

    Seems to me you'd need a service manual to accomplish this, but maybe not.
    The unit may only have one or two filters anyway.

    As I understand it, you will lose a little sensitivity if you tighten up the
    filters, though.

    Mark Z.
  3. Chuck

    Chuck Guest

    I have a Denon tuner whose narrow band setting wasn't narrow enough to
    keep a stronger station on 89.7 mhz. from blanking out a weaker
    station on 89.5. I bought a set of narrower bandwidth filters from
    Digikey in Minnesota and installed them and the tuner works great with
    no discernable decrease in RF sensitivity. Chuck
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