tech stuff – Page 57 – Engineering Radio

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.

Rebuilt tubes

As broadcasters, we don’t really hear that much about ceramic power vacuum tubes these days, as more and more broadcast transmitters migrate to solid-state devices. Once upon a time, however, power tubes were the engine that drove the entire operation. Tubes had to be budgeted for, stocked, rotated, and replaced on a regular schedule. Some of those dern things were expensive too.

Take the 4CX35,000A which was used in the Harris MW50 transmitters. The transmitter used two of these tubes, one in the RF section and one in the modulator. As I recall, new tubes cost somewhere north of $8,000.00 each from EIMAC. Plus, in the A models, there were two 4CX1500A driver tubes. All of which could add up to an expensive maintenance cost every two years or so.

The next best option was to buy rebuilt tubes. Rebuilt tubes were about half the cost of brand-new ones. Some people complain that rebuilds don’t last as long, or only last half as long as the new tubes. I never found that to be the case. I often found other factors that affected tube life far greater, such as filament voltage management, cooling, and by extension, cleanliness.

I can say I never had a warranty issue with ECONCO tubes. I cannot say that about EIMAC, as during the late 90s and early ’00s (or whatever you call that decade), I had several brand new 4CX3500 tubes that were bad right out of the box. These days, ECONCO and EIMAC are both owned by CPI.

I spoke with John Canevari from ECONCO who had a lot of information. For example, as the tube ages, the filament gets more flexible, not less. Most ceramic power tubes use a carbonized tungsten filament containing some small amount of thorium. As the tube ages, the filament can no longer boil off enough electrons and the emission begins to drop off. That is the normal end of life for a power tube. Occasionally, some catastrophic failure will occur.

There are many steps in the rebuilding process:

Dud is received from the field, the serial number is recorded and the tube is tested in.
The tube is prepped by sand-blasting the sealing rings
It is opened
The filament is replaced. In 60-70% of the cases, the grid is replaced. In those tubes that have a screen assembly, 20-60% of those will be replaced.
The Interior of the tube is cleaned
The tube is resealed and tested for leaks with a gas spectrometer
The tube is placed on the vacuum machine. Tubes are evacuated hot, smaller tubes take 12 to 24 hours, and very large tubes can take up to one week.
The tube is nipped off of the vacuum while still hot. When the tube is fully cooled the vacuum scale is normally around 10^-12
The exterior of the tube is cleaned and replated. Silver for tubes that are socketed and Nickel for tubes that have leads.
The tube is retested to the manufacturer’s original specification or greater.

After that, the tube is sent back to its owner or returned to stock. John mentioned that they are very proud of their vacuum tube processing machines, so I asked if he could send along a picture. They certainly look impressive to me, too:

Not exactly sure which tube type these are, but they sure look like 4CX15,000:

vacuum pump on rebuilt ceramic power tubes — Vacuum pump working on rebuilt ceramic power tubes, photo courtesy ECONCO

Econco has been in business since 1968 and rebuilds about 600-1,000 tubes per month. In the past, broadcasters used most of the larger tube types. However, with the majority of broadcast transmitters shifting to solid state, other markets have opened up such as industrial heating, military, research and medical equipment.

RCA BTF-20E

Does anyone need any parts for one? Long-time reader and commenter John has one that looks to be in good shape that he is willing to part with or part out. I had three of these units in Harrisburg and my recollection is they were pretty solid units. When tuned properly, they were low noise and sounded good on the air.

The one issue I had was with the small 100 pf pass-through/by-pass capacitors in the IPA. Several went bad and were no longer functioning as bypass caps. The result was the transmitter would self-oscillate. I think there were seven or eight of them and I replaced them all at once. The exact model of that particular transmitter was a BTF-20ES1, which was one of the last FM transmitters off of the factory floor before the broadcast division went under.

John says:

If anyone needs parts out there, I will probably cannibalize this unit as I have just too many. The separate power supply is inside the garage along with the latest version of the harmonic filter entirely made of copper.

I don’t know if the entire unit actually runs or if it is parts only. It certainly looks like a clean unit. As I recall, Comark bought out all the RCA broadcast parts and service. Comark was then sold to Thomcast, which was sold to Thales which I think spun off its transmitter division to Grass Valley Group. Grass Valley started by making TV master control switchers, routers, and other video equipment.

Anyway, if you are looking for RCA parts for FM transmitters, contact me, and I’ll put you in touch with John.