Re: {Collins} KWM-380 Service Bulletin 11 Audio Low Pass Filter?

----- Original Message ----- From: "Jim Warner" <jim@xxxxxxxxxxxxxxxx>
To: <collins@xxxxxxxxxxxxx>
Sent: Friday, February 17, 2012 10:02 AM
Subject: Re: {Collins} KWM-380 Service Bulletin 11 Audio Low Pass Filter?

SB11 appears to be a marketing supervised engineering folly to produce a field installable pacifier for one large customer to circumvent
logistics of reworking hundreds of A3's...again.
In order to fully enjoy the fidelity of modern SSB and AM shortwave reception that the 380 is fully capable of reproducing, SB11 has to be be bypassed and the actual problem in the AF driver corrected.
Jim WA9Z

What exactly is the problem with the driver in this rig, I am really not familiar with it. BTW, if you mean broadcast AM I don't think its higher fidelity than in the past, maybe lower considering the amount of processing most broadcast stations indulge in plus the limitations introduced by the NRSC pre-emphasis requirements and the use of co-channel digital like hybrid digital radio. If you mean wide-band SSB, it sort of defeats the purpose of SSB for communications, namely conservation of bandwidth and reduction of the power necessary for intelligible speech. Note that broadcast transmitters dating back to the mid-1930s (and some before that) were flat to at least 10khz with fairly low distortion, i.e., below a few percent at high modulation levels.

Richard Knoppow
Los Angeles

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