ICOM IC-7300 .... is a "real" SDR based radio ?

Discussion in 'Amateur Radio Equipment Reviews' started by IW2BSF, Jun 10, 2021.

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  1. G8FXC

    G8FXC XML Subscriber QRZ Page

    It isn't marketed as such, but I would describe it as a Hybrid SDR. The architecture is almost identical to that of the FTdx10 and the processor is the same. I think that Yaesu choose to reserve the description for the more expensive FTdx10 in order to differentiate the two radios and describe the 991 as IF DSP.

    Martin (G8FXC)
     
  2. US7IGN

    US7IGN Ham Member QRZ Page

    I think this way we can call hybrid sdr radio any radio with DSP inside. Like 756pro, 746pro etc. etc. ...
     
  3. G8FXC

    G8FXC XML Subscriber QRZ Page

    It needs to be RF DSP really - there were plenty of radios designed ten or fifteen years ago that had AF DSP and that really does not count as SDR. I had an FT897 which had a DSP button, but that just engaged digital audio filters and noise reduction. If the demodulation is done via balanced mixers, BFOs and discriminators, then it really can't claim to be SDR.

    Martin
     
  4. US7IGN

    US7IGN Ham Member QRZ Page

    This is all conditional and marketing. It seems to me that the stage of signal processing is not so important as the impossibility of eliminating digital processing altogether. For example, in my 706mk2g, I can turn off the DSP, but not in 756pro3. So DSP is necessary part of 756pro3 what made it hybrid anyway.
     
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  5. G8FXC

    G8FXC XML Subscriber QRZ Page

    Not really... To be an SDR, the demodulation, at least, has to be done digitally. Imagine that both the 7300 and the FT897 had been released without an implementation of FM - it could be added to the 7300 with a firmware update and no hardware changes but updating the DSP on an FT897 would never give it the ability to demodulate FM.

    The "hybrid" in "hybrid SDR" refers to the fact that it is still a superhet with an analogue first mixer. The SDR is implemented in the IF which can make it cheaper and also allows the designer to insert a roofing filter to take the strain off the A/D converter. Architecturally, the FTdx10 and FT991 are equivalent to an IC-7300 fixed tuned to 9MHz and fronted up with a tunable transverter that gives the full frequency range. As I said above, this approach has both pros and cons - on the plus side, the roofing filter protects the A/D converter from strong out-of-band signals and probably simplifies the SDR code somewhat because it does not have to work with a wide frequency range. On the minus side, you have more analogue stages before you move into the digital domain and this will inevitably inject some noise.

    Martin (G8FXC)
     
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  6. W7UUU

    W7UUU Principal Moderator Lifetime Member 133 Administrator Volunteer Moderator Platinum Subscriber Life Member QRZ Page

    Great quote :)

    Dave
    W7UUU
     
  7. KU3X

    KU3X Ham Member QRZ Page

    What qualifies him as an expert?
    Barry
     
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  8. KS2G

    KS2G Premium Subscriber QRZ Page

    “An expert is an ordinary fellow from another town.”
    --- Mark Twain
    ;)
     
    F8WBD, K0UO, KU3X and 1 other person like this.
  9. SM0AOM

    SM0AOM Ham Member QRZ Page

    The major "minus" of the hybrid design is that it relies on a local oscillator with a very low sideband noise at close spacings to uphold its superior adjacent channel suppression and overload characteristics.

    To design and manufacture such an oscillator is a major undertaking, compared to the direct-sampling SDR where the close-in noise performance is determined by the noise and jitter characteristics of the crystal controlled system clock, which are much easier to control.

    If a perfect local oscillator could be made, the adjacent channel performance of the hybrid design would be determined only by the overload characteristics of the mixers and the "roofing filters".

    Already in the 80s, analogue receivers were made (Telefunken E1800 with the very expensive synthesiser option AO1710/2) that could handle interferering signals in the order of volts at 50 kHz spacings.

    The direct-sampling SDR has fundamental limitations which are directly derived from the ADC full-scale range and resolution, and cannot be circumvented by any other means than RF selectivity in front of the ADC.

    73/
    Karl-Arne
    SM0AOM
     

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