If I remember correctly it was Collins who first came up with the idea of
using a simple secondary 'noise receiver' to blank the main receiver in HF
SSB mobile installations using the KWM -1 and / or KWM-2A transceivers. The
secondary 'noise' receiver was tuned to a frequency above 30 MHz and had its
own small whip antenna.
The FM receivers in our old RCA 'Carphone' series of VHF Land Mobile rigs
used hard limiting before the discriminator to get rid of impulse noise and
other AM gremlins.
A modified version of the Collins system provides very effective noise
blanking when used in a receiver covering the ham bands. Usually the noise
receiver which provides the blanking pulses is tuned to a frequency clear of
signals just outside of the band in use so that the main receiver is not
blanked by strong unwanted in-band signals, which can be a problem with
blankers driven by in-band noise especially during contests. One name given
to this arrangement many years ago is the 'Evasive Noise Blanker'.
Further improvement in overall receiver performance can be gained by
removing the noise blanking gate, which is usually in the main receiver's
signal path ahead of the IF filter(s), and use the blanking pulses from the
noise receiver to turn the LO injection to the first mixer on and off -
quite easy to do if any 'logic' is used in the LO system. The next
improvement is aimed at dealing with storm static!
Sorry to have drifted off subject!
73,
Geoff
GM4ESD.
Matt Zilmer <[EMAIL PROTECTED]> wrote on Friday, June 06, 2008 at 6:24 AM
At least with the Motorola Syntor X, they used a separate and very
simple receiver to pick out impulse noise and used this secondary RX
detector output to poke holes in the main RX audio. They called it an
Extender and I believe it was only included with the low-band Syntor
X. It is described as a Noise Blanker.
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