BE FM 3.5B problem

[wvnrwnyv]

Hi,

I'm a DJ/Technician (I'm not an engineer in any strech of the term)
at a small station in Vermont: Lakes Region Radio WNYV 94.1FM and WVNR 1340AM
Our station is run by DJs without voice tracking from 5:30am to midnight (EST)

We're having a problem with our FM Transmitter, it's a BE FM 3.5B

We replaced 2 oil capicators in the transmitter a week ago and a ventilation fan on Friday.

Today 6/7/08 the signal has static in the background, and ocassionally has "hiccups". we also had to restart the transmitter at least once today.

We observe our readings from a TC-8 Remote Control, from Advanced Micro-Dynamics inc.

Since noon, our IF amperage dropped to .17 and our EP volts dropped to 3.0 and the signal strength reading from our microwave relay blinks ocassionally (this happens at the same time as the hiccups, which makes me believe there's a problem with our microwave relay too), but stays at about 135, and this is based off the readings from our remote control.

Ok, these are supposed to be our nominal values:

IF amperage: ~.95 (now at .17)
Plate Current: ~4300 (now at 3.0)
Percent Power: ~98-100 (now at 2.0)

My GM went up to the transmitter today and said the meters read barely any amperage or plate current.

I'm not sure what's wrong, neither does my GM, and our engineer hasn't called back today, if you guys can give us ANY insight we'd really appriciate it!

I'll try to give as much info as I can.

 

[SML]

Your engineer needs to call you back. Something in the transmitter sounds as though it has failed.

I hope you don't owe your engineer any $$.

 

[wvnrwnyv]

Haha I don't think we owe him any cash but he does need to call back soon.

From what I tell, the signal appears to be outputing at full power, with only background static, whilst meters say it's flatlining, I wonder if the sensors have given out.

Now, the hiccups with our signal are definately connected to our #5 (microwave link strength) reading, which leads me to believe that somewhere in our microwave relaying system there's a problem, if it's at our relay station, oh lord, I don't even want to think about that.

 

[OKCRadioGuy]

Just a wild guess, but could the problem with the transmitter be bumping the power line enough to make your STL or the remote control looking at it's sample look goofy? I've seen stranger things for sure.

I'd give the guys at BE a buzz about your tranmitter. Get a full set of readings off the transmitter before calling. Make sure you have all the books and schematics available when you call. Try to call during the day of course if you can. If you explain you're not a electronics tech but you'd like to see if there's something simple you could check while waiting for an engineering guy to show up they'll likely be pretty helpful and try to work with you to find the problem.

I have a couple quick questions for you.Does 'IF' stand for intermidiate final or something? Many transmitters refer to the amp after the exciter as the IPA or the intermediate power amplifer. Is your IPA or equivelent a tube amp or is it solid state? I don't know much about your box. Is the exciter putting out the normal amount of power consistanly? If it is, check the IPA. If it's good then go on to the PA section. You changed some caps. Why? What caused you to change the caps? Was it caused from a storm damage issue or something else? Things like this can be a clue sometimes to what else might have shelled out.

If all else fails keep in mind that you can hook your exciter into the antenna and stay on the air if you have a reducer cone. If you're fairly close to your intended market area the exiter trick has been known to work very well until the big transmitter can be fixed. NO station should be without a way to get a exciter into the antenna one way or another. I've had it save my butt many, many times.

Good luck!

 

[wvnrwnyv]

Well, we had to change the caps because one of them blew out, litterally one of them was bulging. I think was from the heat, becasue the shack's (our FM transmitter is about a good 10 miles from our main studio, hence the microwave relay) main vent fan burnt out likely from old age. initally when the engineer started up the transmitter again it had a short, thanks to the packing dept. that sent us the caps. they placed a little wire bridge for safety purposes, and the wire they used was so small that our engineer didn't notice it, but once we heard it short, he found that blasted wire and it ran fine.

To answer your questions OKCRadioGuy, yes IF means Intermediate Final, ergo EP Volts must be Exciter Plate Voltage. And our IPA is tube, everything in our box is tube. Our caps. went out because of the shack's vent failure, when it did fail that shack must have been 110f. Our engineer also commented in passing that he could see some light water damage on the inside base of the box, I could also see some shingles on the roof were missing, so there might actually be some storm damage. From what I could see when I was there, the exciter's meter was bouncing in relation to our aural signal, but always stopped at 100, so it appears to be consistent.

By the way, thanks for the exciter trick, I'll tell my GM to keep that in mind when we go to the transmitter again.

Also, the signal strength for our microwave link, has been very slowly increasing from 138 to 140, and the upper limit I have here for that reading is supposed to be 140, so I'm a little concerned with that too.

Now I'm also looking at out Modulation Monitor too and it's at peak modulation which is set to limit at 107% but the meter peaks at 133% alot, and it happens more frequently before it hiccups, then hits 0% then it goes back up to hover around 80-107% with more peaks at 133%

 

[w9wi]

To answer your questions OKCRadioGuy, yes IF means Intermediate Final, ergo EP Volts must be Exciter Plate Voltage. And our IPA is tube, everything in our box is tube. Our caps. went out because of the shack's vent failure,

Are you sure IF isn't actually "IP"? (I suspect you're reading IP - PA Plate Current and EP - PA Plate Voltage)

 

[wvnrwnyv]

Ahhh, I just talked to my GM, she just woke up a few minutes ago and you're right, they're plate current and plate voltage respectively. I also figured out the sequence of events that lead to the hiccup:

1. FM modulation monitor hits 133%
2. All the readings blink now, (plate current, voltage, % of power, and microwave strength) meaning no reading.
3. aural signal hiccups.
4. Modulation monitor drops to zero and hits 133% again.
5. Readings blink again and the aural signal hiccups again.
6. Modulation monitor drops to zero hits 133% and returns to normal.


By the way, many thanks to everyone replying! Even if we don't find the solution from our exchange and the engineer fixes it, we here at Lakes Region Radio thank you all!

 

[w9wi]

Ahhh, I just talked to my GM, she just woke up a few minutes ago and you're right, they're plate current and plate voltage respectively. I also figured out the sequence of events that lead to the hiccup:

1. FM modulation monitor hits 133%
2. All the readings blink now, (plate current, voltage, % of power, and microwave strength) meaning no reading.
3. aural signal hiccups.
4. Modulation monitor drops to zero and hits 133% again.
5. Readings blink again and the aural signal hiccups again.
6. Modulation monitor drops to zero hits 133% and returns to normal.

Consider that I'm in TV, not radio, and don't do transmitters very often, but...

I'm having a hard time seeing any connection between plate voltage/current/output power and STL (microwave) signal strength. Normally, they shouldn't both glitch at the same time. Unless:

1. There's a problem with the electric utility power at the site - the power is going off briefly.

2. The microwave's weak-signal "squelch" circuit is wired to turn the transmitter off if the link from the studio gets too weak. (I've heard of that being done at a number of stations, to keep from broadcasting a few kilowatts of noise if the microwave link goes down...) Maybe there's something loose at the microwave antenna? (either end, studio or transmitter) Wild guess.

3. The remote is going off the deep end.

It would be interesting to know:
- What the meter readings are doing *on the transmitter*, not over the remote.
- What the meter readings are doing *on the microwave receiver* (at the transmitter), not over the remote.
- Is the electrical power stable at the transmitter site?
- How is the remote unit at the studio connected to the one at the transmitter? (phone line? Subcarrier on the transmitter?)
- Are there any other metering channels on the remote? (tower light current, utility voltage, building temperature, anything like that?) Do *they* blink when the transmitter hiccups?
- When you say "the aural signal hiccups", where is the receiver you're listening on?

To be honest, unless you have unstable utility power (in which case it's the utility's problem!) you're probably going to need an engineer to work on this. Climbing the tower to check out the microwave antenna is a bad idea for amateurs without the proper equipment. (I won't even climb my own ham tower...)

I'm pretty sure the 0/133% readings on the mod monitor are a symptom of the transmitter (and/or microwave) going off, not a source of the problem. If the transmitter is off entirely, of course you're going to have 0% modulation! - and the transient click as it goes off/comes back on could easily glitch the reading to 130% or more. (or you could be briefly broadcasting noise at 130% modulation)

 

[wvnrwnyv]

Well, w9wi

I just checked with National Grid (The FM is in Whitehall, NY while our AM Transmitter and studios are in Poultney, VT) they have no outages or problems so far.

#2 does sound like a possibility

#3 the readings directly off the transmitter, as in the needle meters, when my GM checked were in line with the readings from the remote, which make me believe that the readings are so low that the remote stops transmitting until it can detect it again, causing the hiccups. which would mean that the sensors linked to the transmitter are dead, or close to it.

we have a reciever in the studio that allows us to listen to the FM Broadcast, which is what we do in case it decides to go off air.

I can only hope it starts up in the morning without a hitch (we broadcast from 5:30am to midnight).

 

[TomT]

I would scrape up the money and find a good contract engineer (not a two-way radio guy) to go through the transmitter.

There are all kinds of potential problems, from just tired tubes, to arcing in the high voltage sections that could be causing the main problem with the transmitter. Arcing can eventually destroy parts that can't be easily replaced.

I would also hike on down to your nearest Lowe's/Home Depot type store and get at least 2 "attic fans" or tunnel blowers as they are sometimes called. Find some outside louver panels to match the fans, and mount them to blow air out of the building on the side away from the wind. Then cut a hole in the side that gets the wind --put a louver panel on the inside to discourage critters, you may also want to get some aluminum strips to fashion a bracket for a furnace-type filter. This will help the ventilation--with two fans, if one dies, you still have one moving air. Tube transmitters don't mind hot days ---if you keep lots of air moving through their building.

The STL may not have a problem at all. Get some kind of little amplifier and speaker and some clip leads, (or a BNC to RCA plug adapter) and listen to the incoming signal with the transmitter (and all its blowers, etc.) turned off. If you hear a lot of hiss, or if it fades to noise and back again, then you likely have a path problem. This may require bigger STL antennas, or mounting the existing antennas at different heights. If it is quiet, even though the signal strength meter on the front seems to vary a lot, you may still have a not-so-great path, but plenty of "fade margin" to where this is not a problem.

 

[w9wi]

I just checked with National Grid (The FM is in Whitehall, NY while our AM Transmitter and studios are in Poultney, VT) they have no outages or problems so far.

A problem with intermittent outages that's been going on for that long is probably local to your site. (you're the only customer who's having the outages) It could well be a problem inside your building's electrical panel.

#3 the readings directly off the transmitter, as in the needle meters, when my GM checked were in line with the readings from the remote, which make me believe that the readings are so low that the remote stops transmitting until it can detect it again, causing the hiccups. which would mean that the sensors linked to the transmitter are dead, or close to it.

Assuming the remote at the transmitter is connected to the one at the studio over phone lines, the microwave signal strength reading should work even if the transmitter itself is off. You would see the transmitter power, plate voltage, and plate current readings blink but the microwave strength should be pretty much constant.

If the microwave strength reading is going away at the same time as the transmitter power, then either the power at the site is going out or the low microwave signal is causing the tranmitter to turn off. (through the "fail-safe" mechanism I mentioned)

(probably. I suppose there are other possibilities but IMHO these are the best two)

In some cases the return path for the remote is over a subcarrier on the transmitter. Of course in that case *all* remote metering functions will go out if the transmitter is off - including the microwave strength.

TomT has a good point about arcing being a potential problem - and being able to potentially cause more damage to the transmitter.

 

[rfry]

I would also hike on down to your nearest Lowe's/Home Depot type store and get at least 2 "attic fans" or tunnel blowers as they are sometimes called. Find some outside louver panels to match the fans, and mount them to blow air out of the building on the side away from the wind. Then cut a hole in the side that gets the wind --put a louver panel on the inside to discourage critters, you may also want to get some aluminum strips to fashion a bracket for a furnace-type filter.

It would keep the room cleaner if the air system blew outside air into the building (through air filters), and exhausted it with powered exhaust vents, keeping a slight positive pressure on the room. This avoids inhaling dust/dirt/bugs into the room from gaps around windows, doors etc.

There are other considerations in designing a good air system, such as allowing recirculation to heat the building in winter, and the control system for it. The services of a good HVAC contractor are advisable.

//

 

[TomT]

Yes, we have three fans blowing in, three out, for the 9X17 building that houses our 10k. The incoming fans have a sheet metal hood built over them on the outside, with a bracket system for filters to filter the incoming air. Gets clogged up fast in the spring with bugs--mostly moths, for some reason, but we have a combined site so its easy to keep an eye on the filters.

The incoming fans run off of one thermostat, while the outgoing fans are on separate, staggered thermostats. So usually there is positive pressure unless it gets really hot, then everything is running.

A three wouldn't put out as much heat, but don't know from the description how big the building is. Anything that gets air moving through the building would sound like an improvement. Unfortunately, the solution the local HVAC guy would come up with is either a big air conditioner, or some complicated system of sheet metal to duct air directly out of the transmitter. Neither solution that great and fraught with potential problems. Sounds like they have enough problems with transmitter maintenance.

 

[wvnrwnyv]

Our shack is elevated about 2 feet of the ground, with 3 vents in the floor to drawn in cooler air. we then have an 18" fan with a shutter to suck the hot air out. it's actually fairly efficient, in about a minute or two, it'll take the temperature down fairly quickly.

 

[OKCRadioGuy]

If you have a volt meter try (if you feel safe doing it. BE CAREFUL!!!) to see if the power is stable. I don't think the utility will be able to tell you the whole story. Metering it is the only real way. Since heat played hell on the caps I'd suspect it bothered some other caps in equipement out there. Listening to the STL audio would be a good quick and safe thing to check to make sure that's not a prob. If it is, there might even be a cap inside the STL that got mad from the heat overload.

If you feel like you want to try this (power OFF at the wall and the Jesus stick over ALL the big CAPS to discharge the thousands of volts they can hold) you might want to see if you can change out the IPA tube(s). Also look at the back side of the IPA tube socket for some little brown doorknob capacitors. Just look for cracked or burt up stuff for the most part. Sometimes things show up visiably. With our IPA power out seeming to be low I'd have to think that would be a good place to start. Make SURE that the exciter is set to FWD power out and it's stable on it's power out. If it is, the next step is this IPA section.

 

[wvnrwnyv]

Well, I'm giving all this info to my GM so she can give it to the engineer so they both have a clearer picture of what's going on. I haven't heard anything from my GM today, so I'll keep my ears open both on here and at the station.

Thanks again guys!

 

[wvnrwnyv]

Okay from what we can tell right now (well this is what my GM relayed to me), the meters might not be lying, our transmitter seems to be running on very low power, and occasionally it's hard to turn on. the static and pops appear to be coming from interference from other stations due to our low power output. So we might be able to rule out the microwave link. So I'm thinking it might be something with the exciter?

I'm gonna pass all of this on to our engineer.

 

[rfburns]

Okay from what we can tell right now (well this is what my GM relayed to me), the meters might not be lying, our transmitter seems to be running on very low power, and occasionally it's hard to turn on. the static and pops appear to be coming from interference from other stations due to our low power output. So we might be able to rule out the microwave link. So I'm thinking it might be something with the exciter?

I'm gonna pass all of this on to our engineer.

All of this sounds like either a problem with the incoming electrical or a problem with the high voltage supply in the transmitter.

The TC-8 remote control and studio mod monitor acting erratically - that would be consistant with a low signal level, if the TC-8 is using a subcarrier return for metering.

I'm betting there is something wrong with the high voltage supply.

RFB

 

[busyradioguy]

wvnrwnyv,

What is the reading on the VSWR meter telling you? If you don't see VSWR, look for something like "reflective power". It sounds like a classic case of transmitter RF meltdown to me, so I thought I'd ask.

 

[greg.hahn]

IF amperage: ~.95 (now at .17)
Plate Current: ~4300 (now at 3.0)
Percent Power: ~98-100 (now at 2.0)

My GM went up to the transmitter today and said the meters read barely any amperage or plate current.

Up to now everyone has failed to mention that you are basically off the air. The reason you hear static in your signal is that you have no output power.

I interpret your normal readings to be:

Ip (Plate Current) .95
Ep (Plate voltage) 4300

That would give a DC input power of 4085 watts. If we assume typical 76% efficiency, your total power out would be 3100 watts. That sounds about right for a 3.5 KW tube type transmitter. Does that sound right to you?

But you are saying plate voltage has dropped to 3 volts, and plate current to near nothing, and your RF output meter to zero. YOU'RE OFF THE AIR!!! Whatever you are hearing now is your exciter and possibly your IPA stage coupling through the dead tube stage to the antenna. You may have a couple of watts, that's it.

Now, forget everyone's advice here, except the ones that told you to get an engineer in there. You need someone that knows waht he's doing!