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Re: General Coverage SDR?

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  • Bill Meahan K8QN
    ... Nice fun project. Already exists in the commercial world. The Motorola/Mobat MICOM 2 and 3 series radios are SDR transceivers that see widespread use as
    Message 1 of 36 , Apr 1, 2008
      --- In softrock40@yahoogroups.com, "drmail377" <drmail377@...> wrote:
      > What about general-coverage (seamless 1-30MHz for-example) SDR
      > modifications?

      Nice fun project. Already exists in the commercial world. The
      Motorola/Mobat MICOM 2 and 3 series radios are SDR transceivers that
      see widespread use as HF transceiver for military and commercial
      users. The PERSEUS (designed by Italian hams) and the Quicksilver QS-1
      are examples of ham-oriented general-coverage SDR's. There are (many?)
      others as well including plenty of cell phones. Dave Brainerd's 995X
      board is designed to be the basis of a general-coverage HF
      (trans)receiver as well.

      This is not to say that figuring out how to convert a Softrock, for
      example, into a general-coverage SDR isn't a worthwhile idea. Just
      stating that it isn't new.

      73 de K8QN
    • Terry
      ... That ... current ... range ... Hey Alberto. I ve heard that number a few times, including Joseph Mitola s book (Software Radio Architecture). He suggests
      Message 36 of 36 , Apr 3, 2008
        --- In softrock40@yahoogroups.com, "adibene" <i2phd@...> wrote:
        > --- In softrock40@yahoogroups.com, "Terry" <wb4jfi@> wrote:
        > >
        > > If I understand, HF should have a dynamic range of 130dB or so.
        > > translates to 22 bits, I believe. If appropriately dither is
        > > applied, and subsampling to demod audio for SSB or CW, the
        > > crop of 14 to 16 bit A/D devices should just barely get us there.
        > >
        > > Static crashes and other anomolies that go beyond this 130dB
        > > will still overload the A/D, although only at the peak excursions.
        > Not sure, but 130 dB look to me a bit too many. No analog radio on
        > the market, AFAIK, has such a big dynamic range, but they have no
        > problems to cope with HF signals.
        > 73 Alberto i2PHD

        Hey Alberto. I've heard that number a few times, including Joseph
        Mitola's book (Software Radio Architecture). He suggests that 130dB
        is the dynamic range for HF-RF. He suggests an HF-IF (in the .2-
        10MHz range) sould be 72-120dB. Most other places that I've heard it
        probably reference back to him, although I think I saw it derived in
        at least one other independent book somewhere.

        Most radios are narrow-band, with filters, AGCs, switchable amps &
        attenuators, and other gadgets to translate the level of the
        currently received signal into a narrower dynamic range that the
        radio can handle.

        I think he is suggesting that the 130dB is the minimum for directly
        feeding an A/D converter without overloading, but still reaching the
        HF noise floor.

        Obviously, we can use the same range-limiting (or maybe it's better
        to say range-adjusting) tools if we are using an A/D receiver
        approach. Sticking a preamp and/or attenuator inline will help, as
        long as it can be switched out (or the gain adjusted with an AGC
        loop). Applying filters to remove large unwanted signals (such as
        the US AM broadcast band) is another possibility. I know hams have a
        hard time (with normal radios) trying to work 160M with nearby AM
        broadcast stations, and often resort to filtering.

        But, to a SDR "purist", sticking filters, preamps, attenuators, etc,
        may all be considered band-aids to mask the real issue - not enough
        dynamic range. And, they all potentially hamper optimum reception in
        one manner or another. Like in a traditional superhet, these band-
        aids may be necessary for a while yet.

        I forget where to find the noise floor on the various ham bands.
        But, I'm totally guessing that it's around -128dBm on some HF band.
        To need 130dB of dynamic range with that small a MDS signal means the
        MAXIMUM signal would be over 0dBm! That's a ton of signal. But, I
        hear some people who live near AM broadcast (US), or SW broadcast
        (europe) transmitters may get that strong of a signal. Running
        multiple stations nearby (field day, etc), may also create this

        There was a QEX article in Sept/Oct 2002 (The DX Prowess of HF
        Receivers) that indicated the BDR of a K2 is 133dB (20kHz) and 126dB
        (for 5kHz).

        Feeding an antenna directly into an A/D input may be folly for a
        while yet, especially during electrical storms. I don't think
        anybody plans to have an A/D with that high a dynamic range!!

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