AM transmitter site maintenance check list

As promised, here is the AM transmitter site maintenance check list.  This is for a generic directional AM station with a backup transmitter, generator and an RF STL.

Broadcast Electronics AM6A transmitter
Broadcast Electronics AM6A transmitter

Usual disclaimers apply.

AM site Maintenance checklist

Weekly Maintenance:

A.  Visit site, Check following:

  1. Check critical transmitter values against last logged value
  2. Check forward/reflected power on main transmitter
  3. Check and reset any overloads
  4. Check signal strength on STL against last logged value
  5. Check generator fuel level
  6. General check of building, look in all rooms, inspect for damage from vandalism, Leaking roofs, obvious signs of trouble, take steps to correct.

Monthly Maintenance:

B.  Visit site, Check following:

  1. Do a full multi-meter log, (includes tower phase angles, loop currents), run backup transmitter into dummy load.
  2. Start and run generator for 5 minutes, check block heater, hoses, belts, oil and antifreeze levels
  3. Calibrate remote control meters with transmitter meters, log it*
  4. Check all tower fences for integrity and locked gates*
  5. Complete Items 3, 4 and 5 under weekly maintenance.

Quarterly Maintenance:

C.  Visit site, Check following:

  1. Complete 1 through 5 under monthly maintenance.
  2. Check all air filters, clean or replace as needed.
  3. Check frequencies of all transmitters, STL receiver, and log.
  4. Complete quarterly tower lighting and painting inspection*

Bi-yearly Maintenance:

D.  Visit site, Check Following:

  1. Complete 1 through 5 under quarterly maintenance.
  2. Conduct monitor point readings for all directional antenna patterns*
  3. Check base current readings for day/night towers.  Ratio.*
  4. Clean backup transmitter
  5. Place backup transmitter on air and clean main transmitter.

Yearly Maintenance:

E.  Check all licenses and authorizations for accuracy. Make sure that all renewal cards etc are in public file and are posted at control point.*

F.  Visit site, Check following

  1. Complete 1 through 5 under Bi-yearly maintenance
  2. Equipment performance measurements (NRSC, Harmonics, frequency)*
  3. Complete service of generator
  4. Complete Inspection of towers, check for vertical and plumb, check guy wire tensions, retension as needed.
  5. Check property for anything out of the ordinary
  6. Repair driveway as needed

General maintenance that is completed on an as needed basis

  1. Re-fill fuel generator fuel tank when drops below 50 percent
  2. Empty trash, sweep floors, dust.
  3. Cut/remove vegetation inside tower fences, spray herbicide as needed
  4. Water proof tower fences every 2 years
  5. Paint exterior of building
  6. Replace tower lights*
  7. Paint towers*

*These are FCC inspection items, pay close attention if you do not want a fine.

That is it, a .pdf version of this file can be downloaded here.

Working with Tower Companies

Almost all radio stations use a tower of some sort to support their transmitting antennas.  These towers need maintenance from time to time and only qualified people should perform maintenance on towers.  Hence, the tower company is formed.

405 foot guyed tower with ERI FM antennas
405 foot guyed tower with ERI FM antennas

Over my years of experience, I have dealt with many different tower companies, from one man operations to big corporations that have multiple crews out in the field on any given day.  I have discovered that not all tower companies are created equal.  Not only do tower climbers need to be in good physical shape and be trained correctly in all tower climbing safety procedures,  they also need to be good mechanics so they can actually repair things on the tower.   Climbing a 470 foot tower to repair a strobe light is all well and good.  Once the climber gets to the strobe light, he needs to be able to disassemble it without dropping parts or breaking things, trouble shoot if needed, install new parts and re-assemble the unit, again without dropping or breaking anything.

Applying a RF connectors, installing a FM antenna or STL antenna, repairing light fixtures or conduit all require some amount of manual dexterity and concentration.  Assembling high powered antenna requires close attention to detail.  Any pinched O rings, cross threaded bolts, bent bullets and the antenna will have problems, likely at the worst possible time.

The sign of a bad tower company is if it’s climbers cannot carry out those tasks with one or at most two climbs.  I have a situation on a tower where our FM station is a tenant.  The tower has a strobe light failure near the top of the tower where our FM antenna is located.  They have climbed the tower no less than four times to repair this, and it is still not fixed yet.  Each time they climb, the station has  to reduce power to protect the tower climbers from excessive RF exposure.  Each climb it takes them several hours longer than anticipated to finish their work.

A good rule of thumb, If the defective part cannot fixed in the first two climbs, then the entire strobe unit should be replaced on the third climb.  Even though the strobe units are expensive, by the time they get done paying for all this tower work, they could have bought two new strobes.  Today will be the fifth climb and there is no guarantee that it will be fixed.

I advised the tower owner that they should be looking around for another tower company because these guys aren’t exactly setting the world on fire.

Module swap guys

Nautel V-10 Power Supply
Nautel V-10 Power Supply

Gone is the day when the radio station engineer had to trouble shoot down to the component level, often crawling in and out of transmitters to get at the suspected part.  I for one, spent many a long night at a transmitter site chasing some weird combination of symptoms down to the $0.34 1N914 diode in the directional coupler (see previous post about the MW-50).

It is a skill set now mostly confined to manufactures’ repair departments, for which they charge a pretty penny.  Nowadays, the technician simply slides out one module or circuit card and slides in another.  If that doesn’t fix it, panic ensues.  I know of several class C FM radio stations that are now relying on the computer guy to fix transmitters, because, you know, it’s cheaper.

To be fair, most engineers are contractors and many of those simply do not have the time to trouble shoot to the component level.  So, they ship everything back to the factory then pass the cost on to their client.

Then of course, most circuit boards these days are surface mount systems, which are hard to work on if you don’t have the right tools.  Normally an expensive temperature controlled soldering station is required, as well as a magnifying glass.

All of these things combine make circuit board work something to be outsourced.  Unfortunately, a night spent trouble shooting was often a great learning experience.  I have done some of my best work when my back was up against a wall and I was out of options.

I make the attempt to fix things locally, unless the transmitter or other item is under warranty or not having a spare/attempting to trouble shoot will take the station off the air.  I think it is important to keep abreast of technology and keep my trouble shooting skills up to par.  Besides, I find it gratifying that at least I can still fix things.

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.