Newsgroups: sci.electronics
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From: kludge@grissom.larc.nasa.gov ( Scott Dorsey)
Subject: Re: Help with BA1404 FM xmitter chip
Message-ID: <1991May6.180332.6692@news.larc.nasa.gov>
Keywords: multiplex distortion
Sender: news@news.larc.nasa.gov (USENET Network News)
Reply-To: kludge@grissom.larc.nasa.gov (Scott Dorsey)
Organization: NASA Langley Research Center
References: <1991May4.215501.1653@dg-rtp.dg.com>
Distribution: usa
Date: Mon, 6 May 1991 18:03:32 GMT
Lines: 21

In article <1991May4.215501.1653@dg-rtp.dg.com> miller@dg-rtp.dg.com (Mark T. Miller) writes:
>
>	I've got the BA1404 FM transmitter chip in a Ramsey FM-10 kit.
>	It has a very clean signal if you run it in mono-mode.  However
>	if you tune the fm pilot subcarier up to 19KHz, (the proper place)
>	there is a very audible "multiplex distortion". (noisy squealling
>	sorta' like rubbing a balloon)
>
>	So I have two questions:
>
>	1.) Does anyone know who mmakes the chip so I can get a spec
>		sheet to try to figure out whats going on. (Ramsey
>		simply calls the chip a "custom chip")

Rolm makes it.

The oscillator that generates the subcarrier actually makes something that 
looks like a sawtooth.  This creates a lot of funny sidebands and probably
degrades the sound.  I would not be surprised if this is the cause of the
noise you are hearing.
--scott