Engineering Radio – Page 193 – One Hundred percent Human Generated Content for your Reading Enjoyment

Underground Electrical feeder burn out

In the never-ending saga of things I have not yet seen, we had a 350 kcml 3-phase underground feeder burnout yesterday at our AM transmitter site.

Actually, it happened the day before, around noon. I received a call from the remote control that we were on the backup generator. Upon arriving at the site, I found several trees down on the three-phase primary down the street. I figured that was the cause. After checking the generator fuel supply, oil pressure, temperature, phase volts/amps, I decided that everything was okay and the power company would be along shortly to restore power. I then continued up the road to our FM site to do weekly maintenance.

Upon returning to the office several hours later, I looked at the utility company’s website. They have a pretty cool interactive map application that shows all outages and give restoration times. The area around our transmitter site showed no outages, therefore I figured it had been cleared.

I committed two errors here:

Not calling the utility company myself to ensure that the outage was reported. I assumed that the tree across the three-phase primary was the cause, it was not.
Not calling the transmitter site remote control to check the generator status after I checked the website.

To be honest, I don’t know if I am coming or going these days. With seven radio stations, each with its own transmitter site, three of them Directional AM stations, and three studio locations spread out over a 75-mile stretch, it is difficult to keep up with the small details. Did I mention that I am solo, the engineering assistant position was cut two years ago. But, I am not here to make excuses…

The net result is the generator ran all night long. The next day, when I checked the transmitter in the morning, I was surprised to find the generator still running. Unfortunately, I had an FM station on low power (see post below) that needed to be taken care of first. When I finished replacing the RF module in the FM transmitter, I made my way to the AM site.

I called the power company and then checked the generator fuel, the propane tank was down to 10%. Yikes, better get this taken care of fast. I will say the power company showed up pretty quickly. After some measurements with a handheld meter, it was determined that the underground feeder was open between the pole and the transmitter building.

The lineman was not at all surprised, in fact, he called it before he even went up in the bucket truck. After some back and forth with his supervisor, who came out in a pickup truck, it was decided that they would run a temporary overhead feed to the meter can.

They also did some research in their records and discovered that they (the utility company) own the underground cable and therefore they would dig it up and fix it. That’s nice because otherwise, it seems like it would be an expensive repair job. On a station that makes not have a lot of money.

Repairing a solid state FM transmitter module

We have a Harris Z5-CD transmitter for one of our FM stations. Brand H is not my preferred make, however, it was already installed when we bought the station, so I have to live with it.

This particular site gets hit by lightning strikes often. Normally, it does not affect anything until the transmitter gets turned off for maintenance. Then, almost invariably, when turning the transmitter back on one of the modules will fail. Most often this is manifest when one of the two power supplies shut down causing the transmitter to run no more than 20% power.

The way this is troubleshot is to slide each module out and turn the transmitter back on. When the power supply stays on, the bad module has been located. A confirmation test is to check the MOSFET for a short circuit between Drain and Source. This short circuit condition puts a direct short on the power supply causing it to crowbar and turn off.

So, once the bad module has been located, and the spare module is installed in the transmitter, then what? Most engineers call Harris and ship the module back for repair. Most engineers don’t want to mess with unsoldering a surface mount MOSFET and soldering a new one in. I find it moderately entertaining to fix things myself, so I do not do what most engineers do.

The MOSFET in this particular module is the BLF177, made by NXP. Harris will sell you one for quite a bit of money. You can also buy one from Mouser for about half the cost.

Harris FM Z series transmitter PA module with cover removed

Once the parts are obtained, the worst part of the entire job is unsoldering the old MOSFET. This takes some patience and skill. What I found works best is to melt some solder on the foil leads and get them good and hot. Since this MOSFET is already destroyed, we don’t have to worry about heat, etc. The one thing you do not want to do it actually break the MOSFET open. That is because it contains beryllium oxide, a known carcinogen. Once all the solder is liquid, carefully pry the foil up with a small screwdriver. There are several components that have to be moved to work on this.

Harris Z series PA module with MOSFETS removed

After the old MOSFET is removed, clean up the solder pad with a solder pump and solder wick. I like to use a little liquid flux on the solder wick, it makes things go faster.

Once all the old solder is cleaned off the solder pads, I brush a light coat of liquid flux in the pad. Again, this makes things go faster.

Harris Z series FM transmitter module new MOSFETs waiting to be soldered

The new MOSFETS are very sensitive to static discharge, so I always use a static drain wristband when handling them. I place both MOSFETs onto the circuit board. I then solder them on using as little heat as possible from the soldering iron. Again, the MOSFETs are sensitive to heat and one can easily be destroyed if it gets too hot.

This is the module with the new MOSFETs soldered in. I use defluxing compound to remove all the extra flux. Once it cools off, I test the new module with a DVM:

Harris Z series FM PA circuit board under test, resistance is 3.3 Mohm

If the MOSFETS are good, they will have an internal resistance of around 3.3 MΩ. If the module is bad the MOSFETS will read only a few ohms if shorted:

Harris Z series FM PA module under test, DVM reads 1.6 ohms

That is how you do it. I think Harris charges $775.00 per module to repair. I fixed this one for $240.00, but that is not the reason I did it. I did it for the fun that was in it.

EAS

EAS, or more properly, the Emergency Alert System, is a government-mandated system of encoders and decoders designed by the federal government to alert the public in case of war or other emergency. It and its predecessor, EBS (Emergency Broadcast System) have never been activated by the federal government. Both systems, however, are used extensively by local and state governments for things like weather alerts, amber alerts, etc.

Back in the mid-90s the FCC had a chance to redo the EBS and produce something that was a streamlined and effective tool for public warning. Unfortunately, the EAS system is neither. Rather, it is a cumbersome system of weekly and monthly tests scheduled around pre-conceived notions that how the system is tested every week will be how the system works in an emergency. In practice, this is generally a good theory of system design, but it has failed miserably with EAS. The reasons why are thus:

Most all emergencies are local or at most state-wide events. To this day, very few state and or local government emergency managers would be able to activate EAS for their area. The reason is there is minimal if any interface with the LP-1 EAS stations or station personnel. Ignorance and apathy on behalf of both radio station personnel and government officials is the main culprit.
Most stations are un-maned for large portions of the day. Even if government officials could/did call the station, chances are, nobody would be there. If by chance, arrangements were made to contact station employees at home, they would have to interface with the EAS equipment remotely, which adds complexity to an already complex system.
EAS messages are still mainly relayed from radio station to radio station, the so-called daisy chain network that has been shown numerous times to be unreliable.
The system of SAME codes, FIPS identifiers is not necessarily bad, the application in this case leaves something to be desired. The FCC had a chance to update EAS before the HDTV rollout. One would assume that any improvements could have been built into the new TV sets that are now being sold, but again, that opportunity was missed. For example, I suggested that each TV have a set-up screen option where the owner could input their zip code. They could also choose what types of alerts they would want to know about and even base the alerts types on the time of day. Live in a flood zone, the FFW (Flash Flood Warning) 24/7. Live in tornado alley, TOR (Tornado Warning), etc. The cable companies then pipe in the local NOAA all hazards radio station. All the sudden there is a real national alert system in place using mostly non-broadcast wireless systems. Add to that the ability to sign up for emergency e-mails and text messages for specific areas (many places are currently doing this) and there is multiple message paths.

The system as is not reliable and sooner or later that will be shown with a large-scale failure. Recently, the FCC held a summit with the Department of Homeland Security. The cliff notes version of this event is: Yes, the system can be made better. Let’s keep throwing the same ideas at the wall and see if anything sticks this time. Excuse me if I don’t do back flips, this is the same information that was discussed during the last “let’s revamp EAS” discussion back in 2005 (04-296).

In the meantime, the EAS continues to be a good fundraiser for the FCC enforcement bureau. Which, you know, it is easier to go to a licensed radio station and bust them for not re-transmitting the RMT (Required Monthly Test) than it is to go out and bust some of the numerous pirate radio operators, some of whom are operating in the same city/metropolitan area as a field office.

The shame of it is, it could work without a great deal of cost, very well.

A trip to the FM transmitter site

A few pictures from my last trip to one of our FM transmitter sites. This is a mountaintop site, in as much as a medium-sized hill is a mountain around here. This site has a 2.3-mile road through the woods that is almost impassable 3-4 months out of the year.

Previous engineers have walked up the hill with a toolbox. I can say this with all honesty; not me. In the past, they have also rented a helicopter, and used a snowcat, snowmobile, or an ATV with snow tracks. I’d do those things provided they are safe and insured. As I get older (and wiser), I realize that the only person who going to look after my well-being is me.

Anyway, the trip starts here, at the gate:

Then it goes up the hill:

Some sections are worse than others:

Along the way there are some nice views:

City reservior near transmitter site — City reservoir near the transmitter site

Finally, the gate to the tower farm:

There are two digital TV stations, several cell phone carriers, some government two-way gear, some FM translators, Media Flow, and us at this site. There are also some Ham radio repeaters off to the side in another building. All in all, a pretty RF-intense site.

The view from the top:

The reason why we came:

That is a 24-year-old BE FM5B transmitter. The backup is a Gates FM5G, which aren’t we glad we have a solid reliable transmitter selection for such a remote site. Actually, we were supposed to put in a new Nautel V-10 here last year, but the money was spent on computers instead. Oh well, good thing there will be no computer crashes when we go off the air.

A standard maintenance trip consists of meter readings, comparing the reading to the last set of readings, changing the air filters, checking the remote control and calibrating it to the transmitter, checking the tower light sensor, etc.

Normally, the backup transmitter would run into the dummy load, but the backup transmitter no longer works. Parts are not available to fix it, so we operate without a net. One of the previous general managers asked if that keeps me awake at night, to which my answer was no, not at all.