Suggestions for FM Tuner

FM does it with frequency!
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jthorusen
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Suggestions for FM Tuner

Post by jthorusen »

I am re-thinking the configuration that I want to use for monitoring at the LPFM I am taking care of. I am currently working on a Belar FMS-2 that I was going to interface with the TFT 723 FM monitor that I set up for the station. The TFT has a number of unobtanium parts in it (Z1000 nixies and its main meter among others) and I intend to save wear on life-limited components by turning the unit off when I am not there. (The TFT 723 has been modified by me to kill the power to the nixies and most other circuitry when switched off, leaving the xtal oven hot.)

Of course, the Belar would be useless when the TFT is off if fed from it. There is no convenient on-off switch on the Belar and so I would have to add one or unplug it when not in use. Of course, this means that a precision demodulated air signal is not available when this equipment is off. (Currently, off-air monitoring is done with a consumer-grade digital tuner in the studio.)

I was thinking that if could find a tuner with a good, undistorted wideband output, I could use that to drive the Belar and it could be left on. This would make it independent of the TFT demod.

So, I am looking for recommendations for such a tuner. Digital is OK, because if one wants to listen to the station after a power failure, one can just reset the tuner frequency. This is strictly local listening.

The main requirements are:

One rack unit high - 19" rack mounting... I am short on rack space.
Output suitable to drive the Belar [full bandwidth composite output].

I can build an op-amp circuit to get more voltage out if necessary, but the composite output must be of the best quality.... suitable for making measurements with the Belar. Ideally, there will be a composite output level control, but I can build that into the interface amp if necessary.

Last but not least, cost... this will have to come out of my pocket... as most of the stuff for this station does. :roll:

Thanks for any suggestions,
James K. (Jim) Thorusen
KB6GM
Central Coast Electronics
www.centcoast.com
NW Oregon Consulting Bdcst Eng.
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Re: Suggestions for FM Tuner

Post by TPT »

For a tuner with a clean enough composite output you are probably looking at the Inovonics composite receiver. Unless you can find a used one, probably in the range of $1,600. For around a grand you can buy a used Inovonics modulation monitor which would allow off-air measurement from Bay Country. Last time I looked he had two of them.

Both are 2 RU, but then you could ditch the Belar.
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jthorusen
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Re: Suggestions for FM Tuner

Post by jthorusen »

Thanks, but that's an order of magnitude too expensive. I probably don't need to have sufficient quality to make measurements; just enough to recover the audio in the transmitter room.

I have probably upwards of 500 hours and a fair amount of money into the TFT and quite a few hours and some additional money into the Belar. That configuration is cast in stone.

The ability to run the Belar continuously is a nicety, not a must have. Any old consumer grade tuner would probably do for what I want; it would be nice if it already had composite out so I don't have to go into it and figure out how where to get it. Finding service literature on consumer grade stuff is the pits.

Thanks,
James K. (Jim) Thorusen
KB6GM
Central Coast Electronics
www.centcoast.com
NW Oregon Consulting Bdcst Eng.
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Deep Thought
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Re: Suggestions for FM Tuner

Post by Deep Thought »

It is highly unlikely that you are going to find a tuner which would supply a usable composite output, meet your budget, and fit in 1 RU. Are you just using this as off-air monitoring for the station when you aren't there?

An old mono FM radio is pretty easily converted to "composite out" since they usually only have a rudimentary RC de-emphasis filter on the output which is readily bypassed. Those probably won't fit into one rack unit though.
Mark Mueller • Mueller Broadcast Design • La Grange, IL • http://www.muellerbroadcastdesign.com
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jthorusen
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Re: Suggestions for FM Tuner

Post by jthorusen »

One rack unit would be nice, but it probably isn't a must. Here's a photo:
KWPB Rack Annotated.pdf
(313.66 KiB) Downloaded 74 times
If I can figure out another place for the station automation computer, I'll have all kinds of room.... but the Belar (about three rack units), a 2 rack unit jack field, some sort of amplifier (would like to scrounge a Crown) and the tuner have to squeeze in there. The Belar needs to be right under the TFT and the space on the bottom is limited in depth because of the monster isolation transformer sitting there.

Also, at my age, I'm not wiring a jack field on the floor, and it is too deep to fit in the bottom anyway. It has to go right about where the computer is.

Long and short of it, that thing has to go. Then I'll have some more flexibility as to where I put things. Maybe I should look for another Dynaco FM-5 tuner. I'm not giving up mine, but I do have documentation on it, so I could modify another one. :D

Thanks,
James K. (Jim) Thorusen
KB6GM
Central Coast Electronics
www.centcoast.com
NW Oregon Consulting Bdcst Eng.
wb9fhr
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Re: Suggestions for FM Tuner

Post by wb9fhr »

Fanfair?? 2RU however Its got the outputs
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Re: Suggestions for FM Tuner

Post by ChuckG »

Deep Thought wrote: Sat Apr 25, 2020 12:27 pm
An old mono FM radio is pretty easily converted to "composite out" since they usually only have a rudimentary RC de-emphasis filter on the output which is readily bypassed. Those probably won't fit into one rack unit though.
I modified several of the old Dayton receivers to do just that, to feed translators. Worked fine. Incredibly simple.
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Re: Suggestions for FM Tuner

Post by TPT »

Dayton made a 1 ru composite receiver. Good luck finding one, though.
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Re: Suggestions for FM Tuner

Post by dbuckley »

Deva Broadcast make rebroadcast tuners with composite output, but again, price, the discontinued DB7000 which our station has a couple of, might find on eBay, or the replacement DB7007.
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Re: Suggestions for FM Tuner

Post by TPT »

More I review this discussion--cheapest (though not that cheap) solution is:

A: buy a good quality FM tuner off E-bay--particulary a high-end brand with slide rule tuning (so it stays tuned during power outages)--and use that for the air monitor, and

B: Pickup a used Inovonics mod monitor. It's self-contained, tuneable.
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