Processing

AM Radio discussion. Directional arrays are FUN!
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delahund
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Processing

Post by delahund » Tue Jul 14, 2015 10:40 am

I have our daytime transmitter site that is located at the studio and a night time array located at another site fed with an stl-10. I am upgrading the processing at the studio to an Omnia-One. It can process two outputs. Is there any reason why the processed audio feed through the stl to the night site would be a problem? It would be easier to set one processor instead of two.

delahund
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Re: Processing

Post by delahund » Tue Jul 14, 2015 10:49 am

Disregard. Must have a linear STL... old Marti would not pass all the goodies. My understanding is there would be too many overshoots and lack of modulation control.

ChuckG
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Re: Processing

Post by ChuckG » Tue Jul 14, 2015 10:52 pm

I'd be tempted to try it, bypass the output transformers in the R-10 (later models have jumpers for this) and add a safety limiter of some sort following it. Perhaps an Inovonics 222 or something similar set to nip off any overshoot.
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Chuck Gennaro
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RodeoJack
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Re: Processing

Post by RodeoJack » Wed Jul 15, 2015 5:12 am

All the alarm bells go off on an idea like this, but that's been the case as long as we've had remote transmitters.

The idea of saving a couple thousand is worth trying this though. It might actually be one of the few cases where a 222 makes sense, since you can switch the NRSC filters. I know I'd be tempted to give it a try.

Some things I'd probably look into:

Since all the NRSC stuff is done in the Omnia, could any linearity issues in the STL take you outside the NRSC mask?

Would the positive asymmetry out of the Omnia pass through the STL and safety limiter? Since the Omnia applies the same tilt, asymmetry and low-pass frequency parameters to both outputs, you might need to write separate I/O config files and use an outside contact closure to change how the Omnia works, day/night. No biggie, if you don't really care about pushing the night transmitter or lowering its bandwidth.

Getting a 222 to pass asymmetry from the Omnia, if it will even do it, might make the it active enough to color the audio the Omnia's already processed.

Given the pre-emphasis from the Omnia, would it help / hurt to bypass the pre-emphasis in the STL?

As you say, you could set up one "main" processor, but any further 'esthetic adjustments' to the night output or STL levels would require you to go out to the night site to verify the safety limiter's still happy.

TPT
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Re: Processing

Post by TPT » Wed Jul 15, 2015 4:14 pm

"It's AM folks!"

The old Marti might have some overshoot, but the Inovonics 222 should easily compensate. Since the nighttime site is a different site, it is safe to assume that even with two identical processors at both sites, one (or both) may need some set-up to meet the mask because of the nature of the array, peculiarities of the transmitter, etc. The 222, from the description, should also be able to handle this.

Which old Marti? STL-10 or STL-8. Don't remember on the STL-8 but I know most STL-10's allow you to eliminate any pre-emphasis (there are a couple of side switches on the audio board on the right hand side of the transmitter & receiver. Check the manual.

RodeoJack
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Re: Processing

Post by RodeoJack » Thu Jul 16, 2015 12:35 am

TPT, the curiosity on my part was about how to best configure two processors that are both designed to output an NRSC-compliant signal, adding the STL into the mix which also pre/de-emphasizes. Most would just send the audio out to the transmitter, process it there and be done with it.

There are a couple of stations in my area that might find this configuration useful, if it ends in somewhat comparable performance.

Yes, it's AM, but that's all a few of my owners have, so they still try to get the best they can out of it.

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