I was searching for a way to blank ac line noise without getting the distortion and intermodulation you get when you use the typical transceiver noise blanker. I was researching Collins 316B-2 (uses 40 MHz noise receiver) and ac line-synchronous blankers and was looking at the TS-950 blanker circuit to see how it was implimented when I realized that either the main or subreceiver can trigger the NB diodes for both receivers. So this meant I could use the subreceiver to get the noise signal, and it could be tuned to a quiet part of the band (or even out of band).
By inspection of the circuit diagrams in the service manual, it appears that the noise blanker function can be driven by either the main or subreceiver signal, but that in either case the blanking is applied to both paths. So one can turn on the subreceiver, tune it to a quiet spot in or out of the active band, and use the subreceiver blanking control rather than the main blanking control to get impulse blanking without distortion or intermodulation from in-band signals.
To set up:
NB1 = ON
Main NB = minimum (full CCW)
Sub NB = set for blanking
Sub RX = ON
Sub RX frequency = out of band
This results in quiet, intermod free blanking.
The only problem seems to be a limitation on the spacing between the main and sub receiver frequencies of 500 kHz maximum, but this isn't a big issue. You can listen to the subreceiver output to confirm that there isn't an interfering signal there.
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