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Re: Noise blanker fails on adjacent strong signals.

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  • pd0psb@hotmail.com
    ... That is ofcourse even smarter! ... Take my word on it that the urbanized QRM situation is not alleviating :-) What I do notice is that a new generation of
    Message 1 of 6 , Mar 1, 2012
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      > Linrad puts notch filters on all strong signals to avoid
      > having them into the blanker.
      > The pulses become higher and shorter as compared to
      > what would happen if the bandwidth were limited as you
      > suggest. That makes the blanker work better.

      That is ofcourse even smarter!

      > I think many operators have gone qrt because they
      > feel the situation is hopeless. The best algorithms
      > available today are far from the best that could be done.
      > I have been asking for wideband files a great number
      > of times on a large number od SDR mailing lists.
      > From the response I get I must conclude that QRN
      > problems occur very seldomly. That is quite contrary
      > to my own experience from when I had an antenna.....

      Take my word on it that the urbanized QRM situation is not alleviating :-) What I do notice is that a new generation of radio enthusiats just don't know any better. They think noise levels have always been this high and are a natural part of HF listening.

      As I decided to purchase a second Perseus for local use it is more easy now to make recordings for me. I'll try to make some very specific NB challenges for you if the situation occurs.

      I also found some new forms of QRM. One is said to be genrerated by the widespread Wii playstations. It seems a very fast (over 1kHz) pulsation whine around 2-3MHz. Most NBs don't appear to keep up effeciency with high speed type pulses. (at these frequencies it is ofcourse harder to distinguish pulses from wanted modulation)

      Another form of QRM is multiple carriers with precize spacing over a very large spectrum area. These carriers are reported to be as dense as 4kHz or 8kHz spaced. It would be a good SDR addition if a wideband comb-filter solution for such situations was investigated.

      Best 73
      Paul
      PD0PSB

      >
      > 73
      >
      > Leif / SM5BSZ
      >
    • Leif Asbrink
      Hello Paul, ... Good:-) I look forward to that:-) ... If someone on this list can make a recording I would be very interested:-) ... Have a look here:
      Message 2 of 6 , Mar 1, 2012
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        Hello Paul,

        > As I decided to purchase a second Perseus for local use
        > it is more easy now to make recordings for me. I'll try
        > to make some very specific NB challenges for you if the
        > situation occurs.
        Good:-) I look forward to that:-)

        > I also found some new forms of QRM. One is said to be
        > genrerated by the widespread Wii playstations. It seems a very
        > fast (over 1kHz) pulsation whine around 2-3MHz. Most NBs
        > don't appear to keep up effeciency with high speed type
        > pulses. (at these frequencies it is ofcourse harder to
        > distinguish pulses from wanted modulation)
        If someone on this list can make a recording I would be
        very interested:-)

        > Another form of QRM is multiple carriers with precize
        > spacing over a very large spectrum area. These carriers
        > are reported to be as dense as 4kHz or 8kHz spaced.
        > It would be a good SDR addition if a wideband comb-filter
        > solution for such situations was investigated.
        Have a look here:
        http://sm5bsz.com/linuxdsp/spur/autospur.htm
        Compare figure 7 and figure 8

        The wideband comb-filter will only work if the spurs are
        very stable in frequency and amplitude.

        In case the multiple carriers cover the entire spectral
        range and are close spaced enough to fill the spectrum with
        more than perhaps 30 carriers it is probably possible to
        remove them with a noise blanker. So many equidistant carriers
        indicate a pulse train and if the carriers have the same
        levels the pulse train is likely to fit a noise blanker.

        Recordings with interference problems are always welcome.
        I can provide an ftp site for upload.

        Leif / SM5BSZ
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