tech stuff – Page 56 – Engineering Radio

Where will they put a radio station this time

In the time that I have been working as a broadcast engineer, I have seen some pretty unique transmitter sites. The aforementioned power plant, with the antenna mounted on a smoke stack. The more traditional AM station, is located in a swamp. Other stations both AM and FM combined into one antenna, etc.

This is WGDJ, 1300 KHz, Albany, NY. It is located in what might be a swamp if we were not experiencing marginal drought conditions this summer. The transmitter is located along route 9J. It is a four-tower directional daytime, 10 KW, and a six-tower directional night time, 5 KW. Nothing spectacular, 90-degree towers, spaced 90 degrees apart. Since they are below 200 feet, they don’t need to be lit or painted, which is nice.

The building and all the towers are on 20-foot-high steel stilts. The area is right next to the Hudson River and often floods in the springtime.

The transmitter site sort of reminds me of something I once saw at coastal radio stations WCC and KPH. They were located along saltwater bays.

Phasor with Nautel XR12 transmitter — Phaors with Nautel XR12 transmitter

The station signed on the air in 1963. Initially, it was a 5 KW daytimer only. They added night operation sometime in the seventies. Around 2006 or so, they went to 10 KW day, 5 KW night. The phasor is gigantic for a 5 KW station, or even a 10 KW station. I’ve seen smaller phasors on 50 KW directionals. It has a “Quakertown, PA” nameplate on it, which may be the forerunner of Phasetek. There is a rare art form to creating a functional, yet space economical phasor. Harris could sometimes pull it off, RCA did well, Kintronics seems to be the one of the top phasor makers today.

The main transmitter is a Nautel XR12, which has a very similar look as the V series FM transmitters. The backup transmitter is a MW5A, which, quite frankly scares me. The site was just recently air-conditioned, which means the MW5A transmitter was sucking swamp air through it for 25 years. I do not want to turn that thing on under any circumstances.

All in all, the station has a pretty good signal into the capital city of New York. It nulls to the west, somewhat. Being on 1300, it doesn’t carry as far as some of the other class B AM stations like WROW 590 kHz, but it does alright.

After years of neglect, the station is making a bit of a comeback in the Albany market. They do a lot of local talk radio, which, when the other station is carrying almost all satellite syndicated talk, is making an impression. Being the state capital, there is a lot of fodder.

Continental 816R2 FM transmitter

This is perhaps my favorite model FM transmitter, the Continental 816R2:

Continental 812R2A FM transmitter — Continental 812R2A transmitter, on the air

I have known this particular transmitter for almost twenty years. It was installed new at WFLY 92.3 MHz in August of 1986. I was reflecting on that today, as I replaced the bad 4CX250B driver tube which caused the output power to drop to 10 percent. The power control is via SCRs on the HV power supply, not the more common PA screen voltage adjustment. That means the transmitter comes on with zero PA voltage and ramps up to full power. It makes the whole thing “smooth” like driving a Mercedes.

I have experienced a few overloads, which usually are accompanied by the room lights dimming slightly and the plate voltage turning off. Again, no theatrics; no big blue flashes, no loud arcs, etc. Simply turns off the high voltage and light a LED on the overload board to tell the operator what happened.

Over the last 20 or so years, I think I have had three out-of-the-ordinary problems with this transmitter:

The power supply pass transistor in the 802 exciters failed. This is a TO-3 case mounted on a heat sink, something like a 2N2225 I think. It runs hot. Anyway, the exciter had no 20-volt supplies, which was pretty easy to diagnose.
The SWR foldback did not work during an ice storm. This transmitter feeds an ERI antenna without heaters or radomes. About once every 2-3 years there is an ice buildup, which will cause the transmitter to fold back. In this case, the transmitter overloaded and went off the air instead. Traced back to a bad/dirty connector on the directional coupler.
One of the SCRs exploded while running on the generator. Figured out this was caused by harmonics from the generator exciter. Replaced the exciter with a different version, no SCR problems were encountered after this fix.

I like the Continental tube-type transmitters, they are solid units that perform well and have years of reliable service if properly maintained.

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.