AM transmitter preferences

Engineers are funny.  We all have our likes and dislikes and our reasons for both.  I don’t really like Harris products.  Even when I was in the military, their stuff seemed a little “light.”  I suppose having to deal with an MW-50B transmitter at my first full time chief engineer gig didn’t help that impression.  The MW-50 would “blow up” every six months or so.  I say blow up because that is the only way I can describe it, no overload lights or any other indication of trouble until the blue lightning flashes and thunder from the PA section.  What a POS.

Other Harris transmitters, such as the SUX-1, FM20H, Gates-1 etc have also left me less than impressed.

In order of preference, my choice of AM transmitters would be:

  1. Any Nautel solid state unit.  Nautel makes good equipment that is well supported.
  2. Any BE solid state transmitters.  I favor the A model over the E model, but both are good.  One condition, they must absolutely be well grounded and all of the toroid filters provided by the manufacture must be used when installing.
  3. Any tube type Continental transmitter.  There are older units, I believe 816R but they work well and sound good on the air.

Really, that is about it.

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 burn out 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 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:

  1. 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.
  2. 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 it’s 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 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 hand held meter, it was determined that the under ground feeder was open between the pole and the transmitter building.

The line man was not at all surprized, 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 pick up truck, it was decided that they would run a temporary overhead feed to the meter can.

temporary overhead electrical feeder
temporary overhead electrical feeder

They also did some research in there 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 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 trouble shot 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 crow bar 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.

NXP BLF177 MOSFETS
NXP BLF177 MOSFETS

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
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 screw driver.  There are several components that have to be moved to work on this.

Harris Z series PA module with MOSFETS removed
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
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 wrist band when handling.  I place both MOSFETs on to 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.

Harris Z FM series PA module repaired
Harris Z FM series PA module repaired

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
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
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

Emergency warning siren station
Emergency warning siren station

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 it’s 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-90’s 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 official 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 ads complexity to an already complex system.
  • EAS messages are still mainly relayed from radio station to radio station, the so called daisy chain net work 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 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 “lets revamp EAS” discussion back in 2005 (04-296).

In the mean time, the EAS continues to be a good fund raiser 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.