I've found quite a number of articles discussing noise blankers and the
implementation of such. From my experience with radios on the desk,
past and present, the hardware noise blanker works quite well. On the
other hand, DSP/software noise blankers have always been found to be
marginal.
It seems we are insisting on tighter and tighter bandwidths {filters} to
fight QRM. While at the same time, the use of a tighter the filter has
the adverse effect that causes the noise pulse to be fattened. This
is what Wayne was discussing in his recent post. In another approach,
use a wide filter ahead of the NB thus it can become more effective on
blanking. Wide pulses when blanked will punch holes in the audio.
There's a lot of history with Collins Radio and the implementation of
noise blanking methods. None of these use DSP schemes and in one
system, a separate antenna was used to feed noise pulses to the blanker
circuit. I suggest one research the topic in this vein. One of my
current radios on the desk uses a hardware noise blanker while the other
one uses a DSP/software blanking system. Both radios are from the same
company. It is amazing how much better the hardware noise blanker
performs over the two radios which use DSP or software noise blankers.
73
Bob, K4TAX
K3S, s/n 10163
On 2/4/2016 8:45 AM, Wes (N7WS) wrote:
Maybe this is an opportunity to rant about the K3/K3S noise blanker.
Back on 12/8/15 K2AV wrote: "To those trying to get rid of a certain
noise, remember that there are 21+21+(21x21) combinations of IF and
DSP blanking. That's 483 combinations, not counting variations with
preamp/normal/atten settings."
Now we're adding more?
At the time, I composed a message that I failed to send. It follows:
"Personally, I don't want to "tinker" with 483 possible adjustments.
As I've said before,with a radio with this much computing horsepower
and the design talent at Elecraft I fail to understand why blanking
thresholds and duration aren't nearly automatic.
I would also like to see a technical description beyond the
hand-waving in the manual of how noise blanking is performed. For
example, I fail to see any dedicated delay in the signal path to
create timing coincidence between the noise pulse and the blanking
gate. Perhaps it's inherent in the design, but I would like to see
some words that say so.
If it's going to be necessary for me to set a blanking threshold
(something I think could be automatic) then why can't the radio
generate a blanking pulse that persists as long as that threshold is
exceeded. Why do I also have to adjust that? If the pulse is so long
that intelligibility suffers then that noise isn't amenable to being
blanked and blanking needs to be disabled.
The K3 blanker is okay. Although I no longer have it around to
compare to, I designed a pretty effective one in 1977. Perhaps the
best blanker I've run across was in a lowly Yaesu FT221R 2-meter
multimode. The worst was in my TS870SAT that otherwise was a good
performer and had great ergonomics. I've said more than once that
Kenwood wasted panel space putting in a control for the noise blanker."
End of rant. Eric can close the thread now:-)
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