miller@dg-rtp.dg.com (Mark T. Miller) (05/05/91)
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") 2.) Any Ramsey FM-10 owners out there who have a circuit mod to fix this problem? Thanks in advance to any replies, Mark M. Mark T. Miller miller@dg-rtp.dg.com ...uunet!xyzzy!miller
kludge@grissom.larc.nasa.gov ( Scott Dorsey) (05/07/91)
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