[ICOM] Good effective noise blankers

[Adam Farson]

John, Greg,

Probably the best noise blanker in any amateur HF transceiver is the one in
the IC-7800. This NB is DSP-based, and uses only a fraction of the
processing power of a very powerful TI DSP chip which has only one receiver
to run.

OK...if one does not wish to spend that colour of money, I have found that
the NB in the IC-756Pro3 is quite good at dealing with repetitive impulse
noise such as power-line corona. The NB is the conventional analogue IF
gating type, but when used in conjunction with the DSP-based NR, it is very
effective. (The Pro3 also supports the five US 60m channels, so its
transmitter LPF will not be at risk when transmitting on 5 MHz.)

DSP-based radios behave very differently from analogue designs, but DSP is
here to stay. I actually enjoyed the learning process involved, as it did
not take me very long to discover the powerful signal-management tools which
DSP placed at my disposal. I could not envisage going back to an analogue HF
transceiver or receiver.

Analogue noise blankers all have a flaw inherent in their design. Strong
signals outside the passband of the selectivity filters (analogue or DSP),
but within the passband of the NB roofing filter, will cause the NB to gate
on the peaks of the signals involve. This will cause distortion of the
desired signal. To minimise this distortion, the NB should be set to the
lowest threshold at which it starts to be effective.

Cheers for now, 73,
Adam VA7OJ/AB4OJ




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