General – Page 20 – Engineering Radio

Decomissioning a NEXTEL site

Remember when “NEXTEL (b-b-b-beep), how business gets done…” Well, not anymore. NEXTEL was purchased by Sprint in 2005 and their product lines were combined. Thus, all of these old NEXTEL sites have become redundant and switched off. This particular site was co-located with one of our FM radio clients, which required a power reduction while the old equipment was removed from the tower. I took the time to grab a few pictures of the process:

Former NEXTEL communications equipment room

All of the equipment was removed from the equipment shelter. This site has been switched off since June 2013 and everything in it is destined for the scrap yard. This equipment worked on the 800 MHz bands, which have been re-purposed for Public Safety and Critical Infrastructure, e.g. government users. These racks and radios look like they were expensive:

Speaking of expensive, this site had over 4,500 feet (1,370 meters) of 1 5/8 inch foam coax, which was cut up and scrapped. At today’s prices, that cost $13.25 per foot.

The tower was rigged:

Each of the three panel sector mounts were removed and lowered to the ground.

The NEXTEL antennas were mounted at the 260-foot (80 meter) level of a 395-foot (120 meter) tower. It took some time to remove all of the antennas and equipment from the tower.

Cellular panel antenna array being removed from a tower

I looked on the Sprint website and could not determine if they still offer a push to talk service option (direct talk). With all of the communications options available today, I do not expect there would be much call for it.

For old times sake, here is an old NEXTEL commercial from many years ago:

They did have a good marketing department…

Engineer Killer

That was the title of the email with this photo attached:

Disabled high voltage shorting bar, Collins 820D-2 AM transmitter. Courtesy Pete Partinio

That seems about right.

For many, many reasons, this is a bad thing to do. First of all, the shorting bar is the last point of discharge for the high-voltage power supply. When all else fails, this is designed to route the 3,500-volt plate supply safely to ground. Having a stray 3,500 volts floating around inside a transmitter is never a good idea. Fortunately, it was spotted and removed before anything bad happened.

Secondly, it looks like somebody used a 12 VDC cigarette lighter plug as an insulating device. Wow, did they get lucky. This could have started a fire.

As to exactly why it was there in the first place, I cannot rightly say.

And this is why only properly trained people should be working on transmitters, especially tube-type ones.

Hello, Radiodiscussions.com

I was pleasantly surprised to learn that after a two-month sabbatical, Radiodiscussions.com has returned with an updated look and all of its archived posts intact.

Radiodiscussions.com screen shot — Radiodiscussions.com screenshot

I am pleased that the current owners had a change of heart. Radiodiscussions.com was not perfect, however, it was a good place to gain insight, take part in conversations, read up on rumors and innuendo, follow the flame wars on various threads, etc. In other words, observe radio people in their natural habitat.

Failed High Voltage Contactor

This contactor was used to replace the Furnas contactor installed as original equipment when the transmitter was manufactured in 1986. Furnas is no longer in business, thus the ABB A145-30 was substituted. It was purchased directly from Broadcast Electronics for an FM35A transmitter:

It was installed about 18 months ago and has been in nearly continuous use since. The broken white plastic housing surrounds the contactor coil and is responsible for pushing and holding down the contact fingers.

Looks like the coil is running too hot and damaging the plastic. This resulted in a failure of the contactor to make and no high voltage to the transmitter PA. Obviously a problem. I spoke to BE about this and they did not have a good answer. Actually, what they said was “That contactor is rated for 220 amps,” which is true enough. The only thing that I can think of is the coil is rated for 208 volts and the transmitter is connected to a 240-volt delta service.

A new contactor was ordered and installed yesterday.

I will investigate the coil voltages further, but for now, the 27-year-old transmitter remains on the air.