Well, I guess the first thing I would say about noise blankers for ANY
radio, is that they all more or less have the same limitations for good
performance, thus making comparison difficult unless they are side by side
in most cases.
I have found that the noise blankers in the FT1000MP to be better than more
than a dozen other radios I have had or used. It is critical to adjust the
noise blanker leval adjust to no more than what it takes to remove the
pulse noise.
The reason is that noise blankers are getting there trigger information
from up stream in your early IF stages. All your filters are not yet used,
other strong signals near by affect the agc, and the noise blanker output
can be modulated by other energy in the passband. Then on top of that the
output of the noise blanker is being routed around the rest (or most) of
the IF and is used to blank a audio stage (or much later IF stage) so as to
'remove' the pulse noise. This bypass routing can introduce some of the
energy in the earlier wide passband of the early IF stage into later stages
and be annoying.
Noise blankers try and handle the timing of typical noise pulses expected
to be encountered. Power line, dimmers, ignition noise, and over the
horizon hf radar come to mind. Some types are narrow pulse, some wide, and
that means the timing circuits have to be designed specifically for the
range and type to trigger on. If you make the circuit to broad, it is easly
affected by other energy in the wide passband, and too narrow and it doesnt
handle many noise types. That is why some radios handle certain specific
noise pulses better than others......but no radio is perfect at them
all....its a design issue.
Thats why the FT1000MP has two noise blankers and a leval adjust. Its also
why I sometimes have changed the timing components in some of my noise
blankers to handle what the area I am in tends to through at me.....but
with external RF type blanker systems, I dont suggest that anymore.
Also note that there are hf digital operations of advanced design used by
various government and military agencies that sound like pulse noise, but
are really man made communications. Some users mistakenly think that their
noise blankers are not good because they dont handle those
circumstances.........but those signals are outside the timing of the noise
blanker.
Future new high speed DSP techniques will eventually move up the IF chain
and will be very effective to adjust to just about anything you want it to
handle......including signal mode types..........until then, we live with
the non perfect world of noise blankers.......but I for one and glad that
we have some of the better ones that are out there now.
So the bottom line is that noise blankers can do a near 100% job with no
problem in some circimstances, and not in others.......even for the same
noise. Thats why using external RF blankers can be so effective for local
noise, especially in the presence of strong signals in the early passband
of the radio.
Hope this helps in the comparisons.
73 from Bill Stamps - WD8ARZ
E-Mail Reply to:
wd8arz@null.net
----------
> From: Goetz Linss <dj3iw@donau.de>
> To: 1000mp-list@jehosophat.com
> Subject: [1000MP] FT1000MP noise blankers
To: <yaesu@contesting.com>
> Date: Thursday, November 06, 1997 11:51 AM
>
> Hello MP users!
> What are your experiences with the noise blankers in th FT1000MP?
> On mine (Nov95 made) they are totally useless.
> 73 de Goetz, DJ3IW@DB0RGB.#BAY.DEU.EU
> e-mail:dj3iw@donau.de
>
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