LPFM - STL the one?

Gotta watch those Fresnel zones!
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dmulford
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LPFM - STL the one?

Post by dmulford » Tue Apr 26, 2016 1:36 pm

Our little college LPFM is moving our studio space - which is currently next to our state of the art transmitter.
This poses a problem - we need an STL on a budget.

We've had great luck with a Barix Exstreamer 100 for our web streaming, but looking at people's aversion to Barix boxes for STL's in this thread I'm looking for inexpensive ideas for a LAN STL (we're moving within the same building but to different floors with only network access between the areas).

My options as I see them:

a) run a LONG wire for balanced audio over CAT-5 using baluns between the transmitter and new studio, but worried about noise, etc.
b) bite the bullet and get an IP based STL - which would also facilitate a planned transmitter+antenna move in the nearish-future to a higher roof on campus.

If I go with plan B the usual suspects would be a BRIC (which people seem to love here) or maybe a AudioTX STL-IP from our british friends.
Another brand mentioned in the forums is the TieLine Bridge-IT or the APT IP (which seems similar to the AudioTX. Any other ideas to shop around for besides these brands?

David - engineer and garbage collector
WRKE-LP Roanoke College, Salem VA

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BroadcastDoc
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Re: LPFM - STL the one?

Post by BroadcastDoc » Tue Apr 26, 2016 3:22 pm

I don't think there's an issue with Barix, if they're on the same LAN. It eliminates the typical problems associated with Barix. I know of one college station using a Barix on their LAN as an STL and have had no issues with it.
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dbuckley
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Re: LPFM - STL the one?

Post by dbuckley » Tue Apr 26, 2016 3:31 pm

dmulford wrote:a) run a LONG wire for balanced audio over CAT-5 using baluns between the transmitter and new studio, but worried about noise, etc.
Cat 5 for line level balanced audio works fine. Make sure at least one end has a transformer to avoid issues relating to different ground potentials around the building.

Don't forget that POTS phone is balanced audio over Cat3, and that works just fine over miles.......

TPT
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Re: LPFM - STL the one?

Post by TPT » Tue Apr 26, 2016 5:11 pm

I will be moving a studio this summer for a high school that faces the same problem. Present studio on the second floor of the high school. New studio on ground floor on the opposite side of the building. Administration did not want to move the actual STL antenna off the roof above the present studio to a more exposed location near the front of the building.

However, we were able to get maintenance to pull several hundred feet of CAT-5 from the new studio to the old studio. We will leave the STL transmitter, audio processor in a small rack in that room (it remains a "media" room), and put the EAS equipment downstairs feeding the CAT5.

CAT-5 is nothing more than twisted audio pairs, as such relatively immune to external noise. Not much different than the twisted telephone pairs radio stations used for years to connect to the transmitter. Of course, over several miles the capacitance of the wire affects frequency response, as well as the expected loss of level from that much wire. But a short run from one end of a building to another shouldn't be a problem. Ideally, you should ask the maintenance folks to pull a continuous length of wire & not run it through any cross-connects. This may require drawing a picture for the IT people (if they are involved) who won't understand the concept of "analog." Otherwise they may try to run it through a switch somewhere in the middle.. :roll:

I would terminate both ends in RJ45 jacks and use the studio hub adapters to get the audio in and out of the CAT5.

TPT
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Re: LPFM - STL the one?

Post by TPT » Tue Apr 26, 2016 5:27 pm

Transformers--can cause more harm than good. May not be needed, depending upon the equipment on either end. Your source equipment and processing equipment should be balanced out and in. If they are, but you do have ground loop problems consider it is difficult to find transformers that play nice with stereo audio (especially phase response).

If there is a problem with ground loops then I would plan on spending around $200 and buy a pair of Western Electric 111C transformers. These transformers have excellent phase a frequency response. There are usually a number for sale on E-Bay. On what is a relatively short cable run you will just need one pair--either on the studio end or the transmitter end--depending on the best way to physically mount them.

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Re: LPFM - STL the one?

Post by RodeoJack » Tue Apr 26, 2016 11:51 pm

On the same LAN, the Barix will be fine. I prefer the balanced in/out of the 500, but people use the 100 series with good results. On a stable WAN, the Barix is usually OK.

The Bric is more tolerant of sketchy WAN connections. I also like it in cases where content is mainly MP3... and maybe several generations of it. Using the Barix in this environment just adds one more layer of this kind of compression, which is far from invisible, once you've cascaded it a few times.

Use the Barix if you can't afford a Bric and your audio content is predominately WAVs.

Use the Bric if you've got the money for it. Overall, it's a good investment.

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Re: LPFM - STL the one?

Post by Slab Bulkhead » Wed Apr 27, 2016 9:36 am

TPT wrote:I will be moving a studio this summer for a high school that faces the same problem. Present studio on the second floor of the high school. New studio on ground floor on the opposite side of the building. Administration did not want to move the actual STL antenna off the roof above the present studio to a more exposed location near the front of the building.

However, we were able to get maintenance to pull several hundred feet of CAT-5 from the new studio to the old studio. We will leave the STL transmitter, audio processor in a small rack in that room (it remains a "media" room), and put the EAS equipment downstairs feeding the CAT5.

CAT-5 is nothing more than twisted audio pairs, as such relatively immune to external noise. Not much different than the twisted telephone pairs radio stations used for years to connect to the transmitter. Of course, over several miles the capacitance of the wire affects frequency response, as well as the expected loss of level from that much wire. But a short run from one end of a building to another shouldn't be a problem. Ideally, you should ask the maintenance folks to pull a continuous length of wire & not run it through any cross-connects. This may require drawing a picture for the IT people (if they are involved) who won't understand the concept of "analog." Otherwise they may try to run it through a switch somewhere in the middle.. :roll:

I would terminate both ends in RJ45 jacks and use the studio hub adapters to get the audio in and out of the CAT5.
What this guy said.

Otherwise, if you have to go IP, see if you can get a private point-to-point connection between the rooms. That way, if they take the LAN closet down for maintenance, you aren't off the air as a result.

dmulford
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Re: LPFM - STL the one?

Post by dmulford » Mon Jul 25, 2016 2:31 pm

Thank you all! Great advice.

Looks like we can afford the Comrex boxes - and since we're eventually (hopefully soon) moving our stick and transmitter to another building on campus the Comrex makes sense.

No if only the AC in my office was working on the 3rd hottest day of the year :)

Best,

- David
Engineer and Pastry Chef - WRKE-LP

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