FM – Engineering Radio

Radio Guide; The Magazine

As some of you may have noticed, recently I have been writing some articles for Radio Guide. There are several good reasons for this, but the most important one is education. I believe that terrestrial radio will be around for a few more years. As others have noted, there are fewer and fewer broadcast engineers. Those that understand high power RF and all its intricacies are fewer still. It is important that a cadre of knowledgeable broadcast engineers carry on.

The internet is a great thing. However, it depends on cables of some type to exist. As we know, cables can be damaged. In addition to cables there are routers, core switches, servers and so on. All of that equipment can fail for various reasons. People have been working hard to improve the resiliency of the internet. That is a good cause, to be sure. However small it may be, there is still a chance that the internet can fail. Worse still, this can happen during some type of natural disaster or other emergency. Thus, during such an emergency, Radio can and will function as a vital information source provided that the station is on the air and has a program feed. That is also a good reason to keep the current RF STL paths in place as much as possible.

The Radio Guide articles are a great way to pass along some of that hard earned experience to others. I also want to put supplemental information here for those interested to download. Things like charts, forms, pictures, videos, etc.

What I am planning on is to list the articles here, then put links to any supplemental information provided below that sub heading.

The GatesAir FLX-30

This is the second time I have installed one of these liquid cooled transmitters. This time, it is for WVPS in Burlington, VT. WVPS is the flagship station for Vermont Public Radio. The station is a full class C, a rarity in the North East. The transmitter is located on Mount Mansfield giving it a HAAT of 2,717 feet (828 Meters), which is a good ways up.

This transmitter replaced the previous backup transmitter, a Harris Z16 unit from the early 00’s. There was nothing really wrong with this unit, it just was not a full power backup.

The new transmitter came in two pieces, which is typical for the 30 and 40 KW GatesAir liquid and air cooled transmitters.

New Transmitter, being placed in Radio Transmitter room

For the cooling part of this installation, 1 1/2 inch type M copper pipe was used. This matches most of the other TV transmitters down the hall. In the same building are the transmitters for WCAX-TV, WPTZ-TV, WFFF-TV, and WVNY-TV.

FLX-30 Heat Exchanger, outside with all the others

Liquid cooled transmitter piping, WCAX’s left pair, WVPS right pair

Air purge valve, sight glass, cross connect and distribution manifold, above the transmitter

The highest point in the liquid cooled system is the air purge valve and distribution manifold just above the transmitter. From here, everything slops down to a few low points; the heat exchanger outside, the pump station and the power blocks. This is to make it easier to drain, if that ever needs to happen. There is also an air inlet valve to aid in draining.

All of the cooling work is controlled by the pump station. The fans are connected to VFD modules, which control the flow of air though the Heat Exchanger.

All of this plumbing work was greatly sped along with the use of this Pro Press pipe press tool. This thing is great! No more sweating connections. Dry fit a section to make sure that it is all cut correctly, then go to work with this and it is done in a matter of seconds. Of course, there are no re-dos, so the dry fit procedure is a little more important.

Prior to filling with with Heat Transfer Fluid (50/50 water/antifreeze mix), the system was first pressure tested with air, then filled with clean water for a 12 hour flush. The water was drained out and the filter screen cleaned, then it was filled with the appropriate Heat Transfer Fluid.

Testing into dummy load, TPO is 25,995 watts with -14 dBc HD Radio

Final system checks, remote control test, and HTF top off and the transmitter is ready to go pending the HD Radio installation.

WEZF and WVPS four bay three around panel antenna

Almost Eighteen Years

I do not know what the record is for the longest tube life, however, this particular tube lasted 17 years, 11 months and 23 days. That’s 157,596 hours.

I had written about this almost five years ago: https://www.engineeringradio.us/blog/2014/12/longest-tube-life/

The last one was last fall: https://www.engineeringradio.us/blog/2018/09/i-almost-hate-to-say-anything-but/

Eimac 4CX12000A power tube, serial number RHH108

This was installed new in a Broadcast Electronics FM20T transmitter which was placed on line on June 6, 2001. It lasted until May 28th, 2019 with almost no down time. Towards the end, the emissions started dropping off and we increased the filament voltage up to 10 volts. When you have to increase the filament voltage, that really is the end for a tube.

The new tube was put in and I carefully marked out the date in the maintenance log. The hour meter on the transmitter stopped working several years ago.

Prior to this, the longest tube life I’d experienced was an EEV 4CX35000C from an MW-50B transmitter RF section. When that tube came out, it looked like it have been on fire.

The Broadcast Electronics STX-5 transmitter

Another install, this time a new BE product. I am familiar with the BE FM “C” series transmitter. Those are pretty solid units and we take care of many of them.

This new version of transmitter looks like it has a little bit of Elenos in its DNA. Perhaps I am wrong about that.

The STXe exciter is an all purpose analog/digital unit that will do standard FM stereo, hybrid FM +HD radio, HD radio only, DRM+, or FM and DRM+. I like that. It gives the owner lots of options with regards to future planning. Frankly, I would love to see some DRM+ testing done in the US.

We have actually installed a couple of “C” series transmitter with the STXe exciter as well.

The rest of the transmitter consists of four RF amps and an output combiner all in a short rack. Frankly, if I were ordering one of these units, I’d order the taller rack. Not that I am getting old or anything like that, but stooping over to program the date/time, frequency and power output introduced a slight discomfort in my lower back.

Running into the antenna. At 4.1 KW, 18 watts reflected power is slightly high. This antenna has always had a little bit of reflected power.

"The chicken coop, " WHUC and WZCR transmitter building — “The chicken coop,” WHUC and WZCR transmitter building

The building I installed this in is nick named “The Chicken Coop,” likely because it used to be an actual chicken coop. I am not kidding. The site was originally just the AM station (WHUC). That station had a different transmitter building located some distance away which was fed with open transmission line. This building was put in place sometime around 1969 when the FM station signed on as WHUC-FM (now WZCR). It has seen better days, but we are working on fixing some of the issues with air conditioning and cleanliness.

Remains of open wire transmission line left over from orginal 1947 installation — Remains of open wire transmission line left over from original 1947 installation

The transmitter fired up without any issues and sounds much, much better than the QEI which it replaced.

The QEI transmitter had problems over the years, mostly burned out resistors in the RF combiner network. It has since been scrapped.