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KB2VXA > DSP 12.07.03 00:51l 62 Lines 2763 Bytes #999 (0) @ WW
BID : 10163_WT3V
Read: GUEST DB0FHN DK5RAS
Subj: Re: M0PZT Re: G0FTD > DSP & pulse noise
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Sent: 030711/0123Z @:WT3V.#CNJ.NJ.USA.NA #:10163 [Lakehurst] $:10163_WT3V
From: KB2VXA@WT3V.#CNJ.NJ.USA.NA
To : DSP@WW
Hello Charlie and Andy,
While eliminating impulse noise via the computer sound card may look easy
on paper it's quite a bit more difficult in practice. Impulse noise
eliminators using the receiver's IF has been common practice for many
years so I shall explain the theory that started it all.
A pulse detector similar to a TV sync separator is used to separate the
pulses from the signal ahead of the controlled stage. The pulses are
shaped and timed, inverted and injected into the controlled stage at
equal or greater amplitude than the original. Since they are phase
inverted and of equla or greater amplitude, phase cancellation takes
place and the stage is blanked for the duration of the pulse. Since the
pulses and resulting blanking interval is quite short, the holes are
barely noticable or not heard at all. I have used receivers of this type,
the latest being a GE Mastr2 Lo Band FM mobile unit converted to 6M
operation. Under the very worst conditions there was absolutely no noise
and no disruption of received signals whatsoever.
It seems to me that while such blanking may be accomplised either by a
computer sound card or digital sound editing software, the timing,
inversion, shaping and insertion of the blanking pulses could be jus a
bit tricky at best. I see no reason why it can't be done in theory, but
working it out in fact could prove to be an impossible feat for the
average Ham or someone outside some company's engineering department. If
not done perfecly it doesn't work at all, so working it all out can be a
very frustrating experience.
For that particular reason I suggest checking out a suitable source for
information from someone who has already done it a much simpler way, the
hardware method. I expect that the RSGB like the ARRL has a construction
article somewhere in the archives describing in detail a "little black
box" that will do exactly what you want without all the fuss. Since
impulse noise rather than a broad spectrum of various noises is the
focus, the circuit should be simple and straightforward for that type of
audio DSP.
Then you could do it the RIGHT way there Charlie and buy a rig with IFDSP
which does a far superior job than any sort of audio processing digital
or analog. (knowing grin, really big one too)
Then maybe you just want to download the PROPER software written just for
the purpose???
(OH! You should see the grin NOW!)
ROTFLOLACUTB, TICAATD!!!!!!!
73 de Warren, KB2VXA@WT3V.#CNJ.NJ.USA.NOAM
E-MAIL: kb2vxa@juno.com
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Message timed: 01:30 on 2003-Jul-11 GMT
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