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FM tuners with composite outputs
- Thread starter Studio1
- Start date
Studio1 said:
Inovonics, Dayton, Nicom, RVR and Fanfare all make tuners that would meet your needs. Some are far better than others. There are a lot of tuners built in the 1960's or 1970's that have multiplex outputs. Some were labeled as "Quad Decoder" outputs. Others were mono tuners with a "stereo adapter" output.
On analog tuners, it isn't hard to find the composite signal and just add your own output. It is the audio just before the de-emphasis circuit. A signal tracer or 'scope should make it easy to locate.
That's going to depend on the tuner being used. Modern stuff using a pulse counting detector, probably the composite could be sourced from the input to the stereo demod. Valve circuitry will be somewhat higher impedance, and normally will use a ratio detector or a discriminator... either one you probably ought to buffer the signal to keep from loading the detector. I had an old EICO AM/FM stereo tuner, and the multiuplex stereo adaptor for it, but a cursory look hasn't turned up the tuner schematic. I remember the adaptor used a 'compactron' tube which was essentillay 3/2s of a 12AU7. The system performed at least as well as the stereo encoders of the day.
Studio1 said:
I own or use several of the tuners I mentioned, but none seem to come with schematics. Buffering the output probably wouldn't be a bad idea, and I suspect that most of them do that. They all seem to have a "MPX Output” level adjustment so they are probably just using a simple op amp to isolate it. Even a venerable old 741 IC should work.
On the other hand, I seem to recall that most of the consumer tuners with the Quad output just tapped off before the discriminator and uses a small build-out resistor to keep the smoke from leaving the tuner if you shorted the output. On most solid state stuff a 100 ohm resistor ought to do it.
Studio1 said:
I doubt that you really need a 6 volt output. I had quite a time with our Inovonics tuner until I realized that the trim adjustment was actually a 10 turn pot. Out of the box, it was really hot. Naturally, I was trying to set this in a dark and cramped rack room while standing on my head with a flashlight clenched in my teeth, sweat pouring down onto my reading glasses. Just finding the little hole with a “greenie” screwdriver was a challenge enough. You've probably been there...
Of course, headroom is always nice to have, but if your chosen op amp can do a volt or so, that should be enough for most purposes. Of course, it will do no harm to copy the Inovonics circuit.
True. 6v is really an overkill although they do go on to say it will drive 100ft of coax without a problem.
Yes, a volt or so is more than enough.
The 631 looks like a nice unit. Out of my budget though (for a new one).
I've never understood why stations insist on cramming racks into tiny little back rooms which are impossible to work in
when they could assign a decent sized room with enough space to easily get around the back of the rack.
These days I like to get in on the ground floor, before the plans are drawn up, and specify exactly how much space is
going to be needed and where everything is going to be put.
Yes, a volt or so is more than enough.
The 631 looks like a nice unit. Out of my budget though (for a new one).
I've never understood why stations insist on cramming racks into tiny little back rooms which are impossible to work in
when they could assign a decent sized room with enough space to easily get around the back of the rack.
These days I like to get in on the ground floor, before the plans are drawn up, and specify exactly how much space is
going to be needed and where everything is going to be put.
Studio1 said:
Well they needed a nicer conference room, so cuts had to be made. ;D
Seriously, sit down across the table from a GM and an architect and draw up some station plans and there is a lot of give and take. And the GM often has grand dreams about HIS favorite parts of the radio station. If the engineer of what is now your plant wasn't one to negotiate, engineering very likely got screwed.
Not only that, many times the rack room was designed for something other than what you have today. My rack room was very nicely sized for one AM and one FM. I have zero AMs but 4 FMs...
Studio1 said:
It's worse with translators, where these things are usually installed. Generally they are in a room that is shared with other users of the tower. I have pretty good neighbors, but it isn't at all unusual to find something "unusual" happen, like somebody else's equipment plugged into my UPS, for instance....
And let the record show that UPS or not, the equipment plugged in to the same power source as yours has zero lightning protection & when they get fried, so do you. Isn't co-locating wonderful?Chuck said:
Oh this is verrrryyy verryyy true he he he. Co-location can be a real mess at times.
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