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composite baseband over fiber

Z

zachmorton

Here is a question for the braintrust on this forum. Is it possible to transmit composite baseband over a fiber network to another location? What I'm attempting to do is isolate the studio completely from the rest of the plant, or at least that's my idea. May not be a good idea, but didn't know if anyone else ever pulled it off or not. Locate the Optimod processors in the studio side of the operation, and run the baseband down to the transmitters in another facility.

Any thoughts! And, if it's a stupid idea, just let me know...it's a theory more than anything else right now.
 
Anything made for analog video will pass the 100kHz baseband with no problem. Remember that these were designed for 6MHz wide video.
 
Miles of copper up and down that hill. The thought at one time was to run fiber from the Hill to the tower to eliminate lightning. Most of the hits to the site years ago didn't affect anything in the studio.
Since this time there may have been wires pulled for television that didn't have each wire grounded. Outside shield had no earth ground and would accept induced lightning in the plastic pipe.
If you ran the processors in the engineering room and fibered them down the hill this would eliminate some problems possibly. Is all the video cable still in use or can it be removed?
Memories of years ago. Good luck.
 
Yeah and that is the thought here. Hopefully in the next year, I'll be able to cut all the copper feeds from the hill down to the building. I already have fiber carrying audio from the studio down to the transmitter building. However, my expensive processors seem to get hit more than not when a strike hits that tower. I will be bringing the satellite receivers up on an L band fiber link (already purchased) so that they will not have any copper feeding closures into the building, now to get the processors up there and no more copper! All that would remain would be the STL's and the transmitters...so if lightning gets into anything in the studios, it'd have to be a direct strike on either the phone, power, or something feeding that building. Can't stop it all, but at least isolate it from the 500' lightning rod. And, you're right...you should see the mess that I inherited! Lots of cable with no grounds at all! My first few months were really fun ones...two lightning strikes within two months. Lot's of damage. I don't want to go through that again!
 
I was looking at some of the various composite video over fiber links. One thing that could cause a problem is that many of them only accept an input level of 1v p-p. The audio processor will put out up to 8v p-p. I did find one set that would pass 5v p-p and that would probably be sufficient. Otherwise, you would need to amplify the composite signal at the output end.
 
The best location for a stereo generator is at the transmitter. That has been the rule of thumb for many years. A composite STL that is operating within good signal strength parameters is acceptable, but most installations have moved to digital AES to their transmitters. Moseley offers a digital composite with the Starlink series, but it has not been as popular as they expected. I would treat the illness rather than the symptoms, and fix the described grounding problems. It sounds like the processor is getting hit from the AC mains, not from the tower. If the hits are getting back to the unit through the composite cable, then you have some real issues with transmitter grounding. There could be a number of things wrong at the transmitter building. A good TVSS is a start (Power Clamp etc). Get a copy of Nautel's grounding and lightning protection guide for a diagram of a good grounded building vs. poor one. If I recall, the NAB engineering handbook has some good info on transmitter site grounding. Good luck,
 
I will look at the one we use. We rent STL tower space to a station behind us and we get their composite via a fiber link (and send them marti channels, etc... back).

It was a video product, but they happily made us a special one for our audio purpose. I will post the brand and everything. They were an extremely helpful company. It has run for years with no troubles.
 
This is an odd one. Studio is at the top of the hill and the tower is lower on the hill by several hundred feet. The station had in my 8 years (1986-1994) no lightning strikes at the transmitter. The phones would get hit regularly by lightning hits to the phone and electric on the top of the hill.
The copper down the hill was pulled after a fire in the 1980's and all well grounded. No lightning ever took the path. Then the addition of miles of rg 6 for television was added. These cables were not grounded as well. Lightning became a regular problem, I was told. The problem was for the television side of things though.
The station has or had a static eliminator on the tower. I was suspicious when I was told about it, like a snipe hunt. Watching it allowed me to see the build up during storms then watch cloud to cloud lightning near the tower. There were some lightning hits but they did no damage. Incredible still photos. At one point we replaced components of the static eliminator. Is this still in place? ERI I believe installed it.
Lee Thompson was head of the whole South Central Engineering operation (Nashville, Knoxville, Evansville) at one time. A farmer by background, a former FDA inspector. He had a heart for doing things right. Not sure how long he has been gone.
As far as processors. At the time a single 8000, and one 8100 was in the building. It was WIKY, WJPS (off site in Newburgh at 106.1), and WIKY AM at 1400. The stl systems hardly ever got hurt even in direct strikes.
 
Ours is the Black Box... It works. An 8100XT2 can just barely drive it, though. 8200 up could give it the output level it needed. When operated with 8100 XT2 wide open, we used a clipper on the other side to get the modulation up to 100%.

So, no problems with a modern processor.
 
Chief...thanks for the insight of the addition of the RG-6 cable causing problems. Since we are no longer in the television business, I may just cut those cables off and attempt to pull them out. There are still tons of it in those conduits to the bottom of the hill, and really have no reason to still be there. If indeed you never had problems until after the coax was installed, then that may be a lot of it. There are still television translators and systems running in the building, but none of them are routed to the studio. Programming just comes off of a satellite dish and pipes right into the exciters.

In answer to your question about static eliminators, yes...there are still a forest of them on top of the tower, grounded to earth at the bottom.

I do know the strike we took back in July didn't damage anything in the lower transmitter building, but pretty much eliminated every sound, network, and video card in the studio's. It also destroyed op amps in the Wheatnet audio console, all of the routing switchers for the Wide Orbit automation, as well as took three phone hybrids to heaven. May have just been a fluke...an EMP from the lightning may have gotten into the wiring and really nothing could have been done. According to those who were in the building when it happened, the sky outside turned red for an instance.

As I go through things, I have noticed miles and miles of old wiring that is just cut and hanging in the cable runs, which I suspect are acting as induction points. I am in the process of removing most of it, and rewiring punch blocks correctly. A grand project to be sure, but I'm positive that it will be a good thing once it's all completed.
 
I had an older engineer tell me that box would introduce overshoots (the black one we have). In my IT head, this can't be possible, right... It's all data.

If I am wrong (which I can accept)... Would someone explain how this box could introduce that analog artifact?
 
It all depends on the A/D and D/A converters involved. If it is sampled high enough, then the digital signal itself won't introduce overshoots. The filters and the conversion process could introduce overshoots.

I wonder why nobody has come up with a simple digital "composite" connection to a transmitter. Keep it digital out of the box to the exciter. I know exciters have AES inputs, but sometimes the "overshoot control" and limiters in the exciters are less than great, such as the Harris Digit units.
 
Zach,

Mt. Auburn has a line of telephone poles that run electric and phone all over the top of the hill. The static dissipation can't protect the whole hill. Many times in the past the lightning introduction was through telephone and electric. There was never a comprehensive electric surge protector. Since power has to be switched at the generator, also down the hill, this was maybe still is another unresolved problem. The old telephone system had extra cards for times like that so loss of a card or two was nothing to cause problems.
At one time all sat receivers including the closures for satellite automation were at the transmitter and the automation was at the top of the hill. Even with that no lightning hits that caused any damage. They also ran at that time 3 RCA consoles for the memories. The cabling into the engineering room outside the lunchroom was really ideal and perfectly clean. All the runs were Belden two pair with aluminum shield and a single wire shield. They bunched the spools and used a tractor to pull them at once.
The introduction of television caused many wire runs that were points of lightning induction. With those hits radio was immune. Television sat receivers and switchers kept getting hit. The induction of a grounded hit could cause things to go away in television. Radio was mostly immune. The Orban units had a transformer input which kept lightning out.
When I was there they started a series of LPTV. It was 4, 5, and 52 or 53. The mess of LPTV low channel yagis was really interesting. It looked like a ham radio installation on steroids. Because of the new toy and new programming they even put Master Control for a time on the 3rd floor, which had been storage. Later it moved to the Garden Center just West of the building. This was a neat time as staff kept adding in television and radio still had a large staff compared to most stations then.
At that time Bettie E was still in the office daily. Cyril Williams was nearby causing the tractor to need weekly repair. Linda Goebel RIP was answering phones. The radio stations, television, Muzak franchise, and old school setup was something you don't see much anymore.
 
WNTIRadio said:
It all depends on the A/D and D/A converters involved. If it is sampled high enough, then the digital signal itself won't introduce overshoots. The filters and the conversion process could introduce overshoots.

I wonder why nobody has come up with a simple digital "composite" connection to a transmitter. Keep it digital out of the box to the exciter. I know exciters have AES inputs, but sometimes the "overshoot control" and limiters in the exciters are less than great, such as the Harris Digit units.
Click to expand...

WTPI had studios in downtown Indy and no tower. Modulation Sciences made then a Composite Amplifier. They fed the base band to a building next door (underground and then to the roof) to an stl on the roof in a small closet. It worked well for years. This was farther than the length needed for this project.

With most Omnias there are both analog and AES EBU in outs. In this case I would think you would want to feed both. Analog with a Composite Amp and AES EBU with something else? You have 4 FM stations these days to feed?

It's almost a thought that a short hop stl might also be an option using trango or similar unlicensed. The expense might be similar. Again baseband is the other factor. With the giu built into the Omnias there isn't the need as in the past to locate processing at the studio.

At that location in my time the only internet was through dial up although the traffic and billing systems were networked with rg 8 twinax.
 
zachmorton said:
I do know the strike we took back in July didn't damage anything in the lower transmitter building, but pretty much eliminated every sound, network, and video card in the studio's. It also destroyed op amps in the Wheatnet audio console, all of the routing switchers for the Wide Orbit automation, as well as took three phone hybrids to heaven. May have just been a fluke...an EMP from the lightning may have gotten into the wiring and really nothing could have been done. According to those who were in the building when it happened, the sky outside turned red for an instance.
Click to expand...

Sure sounds like an EMP. I've cleaned up after two EMP's over the years. It was strange...not a single power supply was blown, and the KSU was untouched, although most of the key sets were blown, and every NIC and ethernet switch port was gone. Most, but not all audio devices were fried. I didn't build the place, but it's all properly grounded and neatly done.

zachmorton said:
Chief...thanks for the insight of the addition of the RG-6 cable causing problems. Since we are no longer in the television business, I may just cut those cables off and attempt to pull them out. There are still tons of it in those conduits to the bottom of the hill, and really have no reason to still be there.
Click to expand...

Hope they pull out OK...if they don't budge, try the old electrician's trick of pouring soapy water into the conduit to slick things up...of course, you'll have to mind where the water goes at the bottom of the hill...
 
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