tech stuff – Page 58 – Engineering Radio

FM antenna mounted on the side of a smokestack

If a person were to drive south down I-95 through Bridgeport, CT and look off to the left, they would see a 500-foot smokestack for a coal-fired power plant. Side mounted on that smokestack is a 6-bay Shively FM antenna. The antenna is more visible when driving south. That would be the antenna for WEBE 107.9 Mhz. This is right downtown, therefore, I would imagine this station has no problems with reception.

Bridgeport Power Plant smokestack, viewed from the west

WEBE is a class B FM with a full 50 KW ERP. Most FM’s around here take advantage of a nearby mountain to gain some altitude and thus reduce the TPO a bit. There are several class B stations that run less than 5 KW into a relatively small antenna, but they are way up in the 900 to 1000-foot HAAT range. In this case, the power plant is located right on the Pequonnock River Bay, so the AMSL at the base of the smokestack is only 10 feet. This means lots of watts out and a fairly large antenna.

They are using Broadcast Electronics FM35A for the main and backup transmitters. They were installed in late 1986 and are a little long in the tooth.

They run near a 12 KV plate supply, about 3.8 amps making 34 KW TPO. That goes into a six bay Shively 6 bay 6813 antenna centered at 475 feet, which makes the HAAT 117 meters.

One of the problems encountered at the site is the smokestack emissions. It seems that a fair amount of mercury comes out to the top of that thing. In the past, this has caused major problems with the antenna shorting itself out and burning up transmission line. Because of this, the entire antenna system, radomes, and transmission line is supplied with Nitrogen from this liquid nitrogen tank:

The antenna then intentionally bleeds N2 into the radomes continuously, overpressurizing them, to keep the smokestack emissions out. This type of tank is needed because a conventional N2 tank would last about a day, whereas the liquid tank lasts about 20 days.

The BE FM35A decided to blow a 200 Amp fuse on Friday afternoon:

I had a BE FM30A that would randomly trip the 200 amp main breaker every once in a while. I could never find anything wrong with the transmitter, it would just come back on and run normally again after the breaker was reset. I even replaced the breaker thinking breaker fatigue. Still happened. In the end, we replaced that transmitter. In this case, I don’t see that happening anytime soon.

BE FM35A heavy iron:

Broadcast Electronics FM35A plate transformer

I would not want to replace this thing, it must easily weight 1,000 pounds.

And rectifier stacks:

Broadcast Electronics FM35A rectifier stacks

12,000 volts DC. That will light up any dirt, dust, piece of fuzz, etc. in the transmitter.

It is one of the more unique FM transmitter sites I’ve ever been to. Every time I see it, I am reminded of that song, Smokestack Lightning. My favorite version of that song is the live recording by the Yardbirds

Remotes using a Smart Phone

I was fooling around with my HTC Android phone yesterday and discovered something that has a definite use for radio remotes. An Application called Hertz will record .wav files, which can then be transferred via e-mail or ftp to the studio and played back on the air. The program is pretty slick, it allows sample rates from 8 to 44.1 kHz.

I made a sample recording, the microphone in the HTC phone is okay, a better microphone would sound better. After it was done, I emailed it to myself and listened on the laptop. The email took about 4 minutes for 20 seconds of a 32 kHz .wav file. One could cut that down by choosing a lower sample rate. I have found that 32 kHz is the minimal acceptable sample rate for analog FM. Anything lower than that sounds choppy.

In another potential use, a news reporter could use this to record audio to save and transfer to a computer using a USB cable. The recording time limit depends on the size of the SIM card and the sample rate. Additionally, my HTC Android phone will detect and use WiFi networks, where available, for data services. Using a WiFi network will avoid those 3G data charges and also increase download/upload speeds.

My Verizon plan has unlimited data transfer, so it really doesn’t matter what sample rate I use, your mileage may vary.

Couple the Hertz app with the VNC app mentioned previously, and a person could do all sorts of things remotely with a radio station. The Hertz app is available for free download from the Android app store.

VNC for Android phone

With the advent of computer file storage and automation came unmanned operation. Unfortunately, what often happens with unmanned operations is somehow the engineer becomes responsible for station operation and ends up getting all the phone calls when anything goes wrong:

Traffic forgot to transfer the Sunday log and the station is off the air at 12 am Sunday morning. Call the engineer.
Part-time DJ didn’t read the directions on merging logs, call the engineer.
Windows has encountered a problem and needs to reboot, call the engineer.
The server has locked up, call the engineer.
Silence sensor, engineer’s phone number

I got sick of driving to the radio station when things got out of whack with the AudioVault, so I installed VNC on all the machines. From that point, I could log on from home and see what the problem was. It was great, when traffic goobers up the log transfer, I called the traffic director at home and had her go in a fix it. Untrained operators, called the program director. Unfortunately, I don’t have Bill Gate’s phone number, so the Windows issues are still on me.

All of this was great as long as my laptop was around. Being married, however, I had to occasionally listen to my wife, who insisted that we not take the laptop to dinner or the movies with us. There were those occasional times when it would have been nice.

With the purchase of the Android phone, however, I no longer have to worry about that. Android VNC is a free app that allows an Android phone to connect to any VNC server application. The user can save all the VNC connection information on the phone. It has several mouse options including a touch pad, touchpad mouse, mouse trackball, etc. It connects to most VNC servers: incl TightVNC, RealVNC on Win and Linux, x11vnc, and Apple Remote Desktop on OS/X. 0.4.3. Special commands such as ctl-alt-del are available through the menu. It is also fully zoomable. All in all, I can do almost anything with the Android phone that I can do on the laptop. My wife is thrilled.

It is a time saver.

Upgrading National Weather Service Radio transmitter

If you have ever wondered about those ubiquitous NOAA all hazards radio (formerly National Weather Service radio) stations, wonder no more. These stations transmit on one of five frequencies in the 162 MHz band with power ranges between 250 and 1,000 watts. There are over 1,000 transmitters scattered throughout the country including outlying territories like American Samoa, Guam, Northern Marianas, Virgin Islands, and Puerto Rico.

The original 1958 plan was for these stations to transmit Aviation and Marine weather forecasts. The system was expanded for use by the general public in the early sixties. Since that time, it has been slowly expanding, with the most recent survey concluding that NOAA weather radio station can be received by 95% of the US population.

One of those stations in my neck of the woods is due for a transmitter upgrade. WXL-37 uses two Scientific Radio Systems SR-416P transmitters, as a main and a standby. The programming audio comes from the NWS office in Albany, New York, via TELCO line. The old transmitters are tube type made by in 1976. They are reliable transmitters, however, after 34 years of continuous use, they are getting a little tired. They are also big and bulky and since Scientific Radio Systems went out of business, not been supported.

This year, NOAA is replacing these transmitters with a Nautel NG1000. I have worked with Nautel’s military-grade transmitters before and found them to be extremely rugged. Those transmitters are what the original AMPFET design was based on. Nautel is not the only vendor that NOAA is using however, others include Armstrong Transmitters and Crown Broadcast.

Scientific Radio System SR416P transmitters — NOAA Scientific Radio Systems SR416P VHF transmitters

The Nautel NG1000 is a little thing, taking up about half an equipment rack with an outboard cavity filter and dummy load. There are two drawers, a controller an antenna switch, and a remote control. Each drawer is its own 1 KW transmitter. The GUI is on a laptop, which is what I prefer. If there must be some sort of computer-driven GUI, then make it removable, so that when lightning strikes the 1,000-foot steel lightning rod 25 feet away, it doesn’t get blown up. Each transmitter is connected to a 30 AMP 240 Volt breaker via a 4-prong twist lock plug.

Nautel NG1000 transmitter — Nautel NG1000 NOAA transmitter

The antenna for this station is near the middle of this 1,000-foot tower, thus the station gets excellent coverage with a TPO of 1,000 watts.

American Tower, Highland, NY — American Tower site, Highland, NY

On a related side note, the computer synthesized voices normally heard on NOAA stations took several years to evolve. Remember when this began back in the mid 1990’s with “Paul.” Several years later, “Craig” and “Donna” were introduced. Finally, “Tom,” is able to change voice inflections for emphasis. When I was in the Coast Guard, we did high seas synopsis and forecast on HF without aid of computers. At times, especially during typhoon season, it got a little busy in the weather broadcast position. There are advantages and disadvantages to both methods. Personally, I’d rather hear a human voice, especially in a crisis.