[Milsurplus] Early BC-312/342 Noise Suppression Ckt.

[W7QHO at aol.com]

All,

Questions on this feature, included in 312/342 models up through C, come up from time to time.  The feature was dropped in D and later models and maintenance instructions were to remove the components if any servicing was required.  My 342A sports the plugged up holes on the front panel where this was done.  Always wondered just how the feature was used and how well (or poorly) it worked.

While browsing through TM 11-273 (April 12, 1941, SCR-193) recently I came across the following set of instructions which I thought might be of general interest to the group:

"c. To reduce engine ignition interference on the 1500 - 3000 kc frequency bands.

(1) (Refers reader back to a page and half of general turn-on insturctions. DD)

(2) Connect the signal antenna to the SIG ANT terminal.  Disconnect the noise antenna.  (The noise antenna consists of a piece of shielded wire connected between the source of interference and the NOISE ANT terminal on the receiver.)  Adjust the NOISE ADJUST control to receive maximum noise output.

(3) Disconnect the signal antenna.  Connect the noise antenna to the NOISE ANT terminal.  Adjust the NOISE BALANCE control to receive maximum noise output.  The noise output should be equal to that secured in (2) above.  If the noise outputs are not equal, relocate the pick-up end of the noise antenna until they are equal, and readjust the NIOSE BALANCE control for maximum noise output.

(4) Connect both antennas.  Adjust both NOISE ADJUST and NOISE BALANCE until the minimum noise output is secured.

(5)  If noise reduction is unsatisfactory, it may be necessary to move the pick-up end of the noise antenna a number of times, repeating the above procedure each time until the best results are obtained."

Can see GIs getting frustrated pretty quick trying to do this.  Also, the setup would likely be knocked out of balance at the first bump in the road.  Not surprised the feature was dropped.

Anyone have real life experience with this?


-- 
Dennis D.  W7QHO
Glendale, CA