multiplex decoders

[Opcom]

I know it is off topic but it is old tube stuff related. Has anyone used/or uses one of these things recently? They go with an FM mono tuner.

In making room to pack up some big boxes of stuff, I had to move some hi-fi gear and dicovered an Eico MX-99. I have not used such a thing recently (well the last 15 years..), just an all tube mono setup.

So, I think it'll work fine but I read that there are other subcarriers (92 kHz SCA and 52KHz RDS databursts) in use today beside the old 67KHz one that was traditionally filtered out. Has anyone who uses a standard old fashioned analog MPX decoder found this annoying? Will I need to add filter(s) for those subcarriers?

[WQ9E]

Patrick,

I don't think the new subcarriers will be a problem for your decoder because a lot of vintage receivers from the time before all of the new stuff was added are still in use without problem.  I have one early 1970s Marantz setup in my home office and another in the parlor radio room and neither FM tuner does anything it shouldn't (well besides playing rap music if I don't tune quickly enough across the band).

[N1BCG]

FM stereo decoders receive the 38 kHz L-R signal and use the 19 kHz pilot signal to align with the baseband L+R signal.  Some fiddling with it might allow you to tune in the other subcarriers like you mentioned... 57, 67, 92.

Stations, particularly in metro areas, would use these for distributing Muzak and brokered programming to listeners with fixed-tuned receivers. Many minority programs used this system as well as special subscription services such as reading for the blind, etc. Our stations used subcarriers for cueing talent at remote broadcast locations. It was often entertaining to hear the "behind the scenes" chatter.

[flintstone mop]

Here is some handy info on the FM broadcast spectrum


http://en.wikipedia.org/wiki/HD_Radio

Fred

[WA1LGQ]

I have not tried this in a looong time but I used to connect the fm detector output to the input of a LF receiver and be able to tune around and see what subcarriers were there. This may help you troubleshoot any subcarrier interference issues.
Larry