Troubleshooting an intermittent STL ( maybe )

[DonIam]

I have a STL path that is around 10 miles with the TX antenna at 200 feet and the RX antenna at 500 feet.

The installation has been in place for ten years using a 2 watt Harris CDLink.
AES from Optimod AES to Digital Harris CD exciter.

Lately, we have had several 10-30 second audio dropouts..... not often, but occasionally... usually between 8P and 10P.

The "minutes-since-last-error" timer at the receiver will correspond with the dead audio.

Usually the "last error" counter is maxed out at 9999999999999999 ( long time since failure )
when I do my weekly maintenence runs.

Short of finding ( borrowing ) a digital RX that I could put near the STL TX with a silence sensor what could I do
to confirm the problem is either path related, or transmitter related .... receive quality is 100% with 130mv indicated.
The STL TX is too far from from the board operator for a quick look at the RF Output.


Don

[BroadcastDoc]

Could you wire up the receiver "Fault" and "Warning" pins to your remote control system? That might at least get you started in the right direction.

[chrish]

Had this intermittent problem twice, first was at WZLX-FM Boston, STL signal would intermittently die for minutes at a time but of course by the time I got to the transmitter to see what was going happening to the Moseley PCL-606 Composite
receiver the problem had gone away. This started happening on a more frequent and frightening basis. Changed to backup transmitter with no luck. I had one STL receiver feeding each FM-25K and once again the problem would rear its ugly head just when I thought I had it isolated. Sheer panic set in and I called New England Bell and ordered an emergency stereo analog pair installed and pleaded emergency. Having worked with many friends over many years at New England Bell sales and engineering along with the Radio and TV board they performed miraculous service for me. Within 4 hours of moving the backup 8100 Optimod to the transmitterfeed by the new lines into one FM-25K the STL signal died....died ....died. Never to return.
The date was December 24,1986 at 12:45 PM. I celebrated Christmas at Midnight Mass with an affirmed belief in God. On December 26, a trip to the transmitter revealed no STL signal on either receiver whatsoever. The studio Transmission
end showed normal power out with no vswr problems.
As it so happened we went into a period of severe winter weather with very high winds which made tower climbing to to inspect the receive dish impossible for almost two weeks....no one would climb. When it was finally safe guess what the tower guy found? RF from the bottom bay had over time eaten away the flexible jumper joining the Heliax to the dish. The dish was moved down as far as possible but it was on a short tower on top of Prudential Center with not a lot of wiggle room.
I was sure glad I followed my gut instincts and has a set of land lines installed. They remained in service until the studios were moved. No ISDN back up in those days.

Second STL nightmare was a newer Composite Moseley system at WGIR-FM Manchester....no backup telco lines, I was doing some partime work for them while they were converting over to Prophet, the treck from downtown up to the mountaintop transmitter was about 45 minutes one way. On an ocassional intermittent basis audio started bursting with garbage like something was getting into the STL lasting for a minute or two. A trip to the transmitter would show nothing as the problem was long gone. It next happened when I was in Boston 90 minutes away, of course when I got there no sign of problem and repeated itself over the following couple of weeks. Once again with Gods help or just a stroke of luck
the nextime I was at the transmitter something caught my attention out of the corner of my eye. The Moseley Composite STL receiver was going ballistic (not set up with one receiver feeding each transmitter...that was changed) but not dropping completely so the auto transfer panel would flip to the other receiver. Manual switch over showed the problem was indeed receiver #1 talk about luck catching it in the act, could have watched it for days before it happend again, maybe never actually seeing it happen

[PID_Stop]

Lately, we have had several 10-30 second audio dropouts..... not often, but occasionally... usually between 8P and 10P.

Hmmm... dusk, when street lights come on. We had a similar problem with one of our network satellite links several years back, and it took about a month before we discovered the culprit: a high pressure sodium light fixture on the side of our neighbor's building. For whatever reason, it would radiate a lot of hash while it was warming up, and then behave itself for the rest of the night.

As it turns out, my boss finally spotted it: he was in his truck listening to an AM station when the blast-o-crap hit, and saw the light flickering before it finally snapped on.

I truly hate this kind of intermittent problem.

-- Jeff


* Edit *
I didn't notice the original date on this thread... clearly the sun isn't going down that late in January (at least, if you live in the northern hemisphere). The coffee hasn't quite kicked in yet.

[BroadcastDoc]

No, but that's great information if someone else happens to come around trying to solve a problem!

[NECRAT]

Lately, we have had several 10-30 second audio dropouts..... not often, but occasionally... usually between 8P and 10P.

Hmmm... dusk, when street lights come on. We had a similar problem with one of our network satellite links several years back, and it took about a month before we discovered the culprit: a high pressure sodium light fixture on the side of our neighbor's building. For whatever reason, it would radiate a lot of hash while it was warming up, and then behave itself for the rest of the night.

As it turns out, my boss finally spotted it: he was in his truck listening to an AM station when the blast-o-crap hit, and saw the light flickering before it finally snapped on.

I truly hate this kind of intermittent problem.

-- Jeff

We had a VERY similar issue at our master control facility up near Springfield. Our FOX receive antenna was taking hits, very frequently. Upon further investigation, it was Jim Ferrone who suggested this to us. He said "check your parking lot for any flickering lights or dead ones". Well sure enough, the parking lot light, located directly behind the Fox antenna as a matter of fact, had died. Shut the power off to the fixture, the hits went away.

Another odd interfereing factor we found too, are lawn mowers and any small motor. When they mowed the lawns near the satellite dishes, our ABC receivers would unlock and go crazy.

[w9wi]

We had a VERY similar issue at our master control facility up near Springfield. Our FOX receive antenna was taking hits, very frequently. Upon further investigation, it was Jim Ferrone who suggested this to us. He said "check your parking lot for any flickering lights or dead ones". Well sure enough, the parking lot light, located directly behind the Fox antenna as a matter of fact, had died. Shut the power off to the fixture, the hits went away.

Another odd interfereing factor we found too, are lawn mowers and any small motor. When they mowed the lawns near the satellite dishes, our ABC receivers would unlock and go crazy.

Less surprising but equally able to mess up a downlink.. are radar detectors. Our NBC dishes are in the parking lot, and we've had to put large signs on the fence warning employees to unplug their detectors when they park...

[50ohmload]

I had the same sort of problem, intermittent audio dropouts, on a Moseley Starlink delivering AES audio. In my case, there was no correlation with the time of day. The problem turned out to be occasional overmodulation from an adjacent-channel analog STL located within the beamwidth of the receive dish. The problem was observed by checking the incoming signal at the receive site with a spectrum analyzer.

With a 500 foot receive dish height, It is quite possible your dish is picking up other signals along with your STL transmitter. I have always heard it is best to use the lowest possible height for the receive dish to minimize the probability of pick-up from other sources.