Tag: FM

Frequency Modulation

Fordham University WFUV

Over the last several months, I have been helping out in a small way with WFUV’s new transmitter installation. George Evans, CE for WFUV, and Bill Weeks of Wolftron Electronics did most of the work. This project’s location is unique; the transmitter is in an equipment shelter on top of the Montefiore Medical Center in the Bronx. That complicated the removal of the old transmitters and installation of the new transmitters.

WFUV tower atop the Montefiore Medical Center

This is the top of the Montefiore Medical Center in the Bronx. The building has 28 floors. To access the transmitter, one needs to go up another flight of stairs to the roof. Go outside onto the roof and take two more flights of stairs to the transmitter shelter just below the tower. Those stairs can be seen as a thin wispy thing on the left of the elevator building.

WFUV tower, close up

At the top of the tower, the two-bay Shively antenna is for WVBN 103.9 Mhz. WFUV 90.7 MHz is the six-bay Shively just below that.

BE FMi 703 (FM-10S)

These are the transmitters being replaced. There are two of them running combined for a TPO of 14.2 KW (including the -14 dBc HD subcarriers). They are about 20 years old.

The before picture; combined BE FMi 703 transmitters

As you can see, there is little room to work in this space. The old transmitters needed to be removed from the room, hosted down two stories to the main rooftop, wheeled around to the door, and then lowered another flight of stairs to the 28th to the elevator.

It makes me tired just thinking about it.

BE FMi 703 (less RF modules and power supplies) being lowered to the rooftop level

Out with the old, in with the new.

GatesAir FAX15K being hoisted from the roof up to the transmitter shelter

The GatesAir FAX15Ks made the trip up safely. Able Rigging from New Jersey did all of the moving into and out of the shelter. The two transmitter chassis, all of the boxes containing the exciters, RF modules, power supplies plus a 25 KW dummy load, and the cut-up for scrap Myat variable T antenna combiner were removed in one go.

The after picture; GatesAir FAX15K transmitters, two cabinet version

The FAX15K’s are in the shorter cabinets (requires two) because the taller cabinet would not fit in the elevator.

FAX15K with back doors removed, power block, combiner, directional coupler, and RF output flange.
3-inch coax switch and RF plumbing

The output of each transmitter goes to a 3-inch coax switch. The bottom port of the switch goes to the Shively filter (thence to the antenna), and the top port goes to the 20 KW dummy load.

3-inch coax switch
Bill Weeks routing control wiring to coax switch
WFUV CE George Evans, heading to the job site
“How many more times do I have to climb these stairs today?”
But the view is great! Mid and upper Manhattan in the distance
Your author is about to tell a sea story…

I enjoyed working on this project.

How long should a transmitter last?

This Broadcast Electronics FM3.5A is 40 years old. There was a small problem that took the station off the air for a couple of hours this morning. The high voltage shorting solenoid fell apart, causing the 40 amp breaker in the service panel to trip.

BE FM3.5A defective shorting solenoid

These types of failures will become more frequent as the transmitter ages. Things like air switches, blower motors, tuning and loading mechanical assemblies, circuit breaker fatigue, plate rectifiers, screen and plate bypass capacitors, exciter and controller fans, etc. The list of potential failure points can get quite long. The fact is, nothing lasts forever.

Manufacturers nameplate

There is no backup transmitter for this site and there is no easy way to get a temporary unit on line, if needed. This is not the oldest main transmitter that we service with no backup. That honor goes to a CCA DS-3000 built in 1970.

The question is; how long should old tube transmitters be kept in service? Also; how long should we (an independent service company) agree to maintain them? The temporary solution for the above failure was to remove the broken shorting bar and turn the transmitter back on.

Broken shorting bar removed

That creates a safety issue for anyone who may need to work on the transmitter before the replacement arrives. It also creates a potential liability issue for my company.

I put a big label on the back door indicating that anyone doing service needs to discharge the power supply capacitor with the grounding stick (which they should be doing anyway). But I will feel better when the shorting solenoid is working again.

Rohde Schwarz Test & Measurement Fundamentals

I found a great resource for learning about test and measurement on Rohde Schwarz’s YouTube channel. Each video is about 5 to 15 minutes long and covers the basics of RF test equipment, measurement parameters, and definitions.

Rohde Schwarz Test and Measurement Fundamentals

Measuring RF systems is an important part of Broadcast Engineering. Many folks think that RF plants are going away, replaced by all IP content distribution. I disagree; Terrestrial Broadcasting will be around for a while yet. AM and FM radios are still ubiquitous in cars, homes, businesses, etc. There is no other information distribution method that is as simple and robust as over-the-air broadcasts. That is why Federal Emergency Management is still spending money on hardening broadcast facilities.

The Internet and Mobile Data in particular are susceptible to failure in emergencies. Cellular networks were almost useless due to congestion or system outages during the 9/11 attack or a natural disaster such as Hurricane Sandy.

Radio still has a role to play.

As the older Broadcast Engineers retire, there is a dearth of qualified RF specialists who can make accurate measurements on antenna systems, filters, and other transmission system components. There are very few mentoring opportunities, especially in commercial broadcasting. Gone are the days of several engineers on staff, when there was time to teach the younger people some hard-learned lessons. One of the reasons I write this blog is to pass along some of that knowledge to others so that the industry might survive.