We just finished our 3rd annual February ice storm. It is becoming somewhat of a tradition in these parts. After shoveling the driveway this morning, I sat down to enjoy my nice hot coffee. While doing that, I figured I would check some of the transmitters to see how things were going. That is when I noticed this:
The reflected power is much higher than normal indicating potential issues with the antenna deicers. I knew something was wrong after a quick call to the Burk, which stated the deicers were on. A quick double-check showed that the reflected power had increased by another 75 watts, so a nice drive to the transmitter site was in order.
Road to the transmitter site
Indeed, the controller had turned on the antenna deicers.
Antenna deicer controller
Using a clamp on amp meter, I saw almost no current on either leg of the 240-volt circuit. In the meantime, the backup antenna had 2 amps on each leg, which is normal. Then I noticed this:
Antenna deicer relays
The relay on the right shows signs of overheating.
I moved the Main Antenna circuit over to the aux antenna relay to get things going again. The current on each leg of the main circuit is 4.2 amps. Over the next 45 minutes, the reflected power returned to normal.
Other transmitter sites to the north in Albany have had similar issues. Unfortunately, those antennas do not have heaters or radomes. Thus, the only remedy is reducing power until the transmitter stays on.
I also noticed that when there is an antenna problem, the station does not sound as good as it normally does because of the bandwidth restrictions adding distortion in the frequency domain.
Recently, I installed this very nice GatesAir FAX60HD.
This project was for WPGC, Washington, DC. WPGC (Prince George’s County) is an Audacy station with a Hip-Hop and R&B format. I was listening to The Good Morning Show on my drive from the hotel to the transmitter site, and those guys were hilarious! It’s nice to hear a well-programmed radio station.
It is always fun to accept new and interesting challenges. This is, to date, the largest transmitter either AM or FM that I have ever installed. Previously, I installed several FLX-40 units, which is quite a bit of power for the FM side of things.
MSC unit with touch screen pad controls both transmitters and exciters
This transmitter combines two FAX30 transmitters and is controlled by an MSC unit. The content stream for HD comes from an FMXi4g, which has several great features.
BDI inline watt meter
This station’s TPO is 45.7 KW with the HD carriers at -14dBc. While this is a class B station with an ERP of 50 KW, the four-bay half wave-spaced antenna requires a lot of wattage to make that TPO. This is a largely residential neighborhood, which is, I surmise, the reason for the half wave-spaced antenna.
WPGC main and backup antennas, Capitol Heights, Maryland
I was told that this is not the greatest part of town. The station has had some theft of outdoor air conditioner equipment in the recent past. That being said, it is much nicer than many areas we normally work in the NYC metro area. The transmitter site has been here since the station signed on in 1948.
WPGC transmitter siteFAX60HD power supplies and power amps installed
It took a bit of time to install the 42 power supplies and 48 power amps. The power amps were installed in the same slots as during the factory test cycle. Thus the data on the test sheet matches the data seen on the transmitter GUI when we turn it on.
FAX60HD cabinet interconnects completed
All of the cabinet interconnects; RF plumbing, grounding, AC supply, sample lines, and various control lines were completed.
Transmitter hybrid combiner for the two FAX30 transmittersFAX60HD, WPGC-FM Washington4 Inch Dielectric coax switch with 60 KW loadWPGC 4th harmonic
Most of the harmonics (2-10) looked like this. However…
WPGC 5th harmonic
This is something interesting that came up during the proof. When measuring the harmonics, most of them were in the -130 dB range. This one is slightly higher than that, which is due to the proximity of WFDC-DT on channel 15 (476-482 MHz), 1000 KW ERP about 10.6 miles away. Their signal was coming back down the transmission line from the FM antenna. This is a good demonstration of how other unwanted signals can get into the final sections of transmitters which can cause intermodulation mixing products. In this case, the FAX60 has several low-pass filters that remove this and other signals before that happens.
This is replacing a pair of combined BE FM25-T transmitters that were getting a little bit long in the tooth. The air staff has commented on the noticeable improvement of the station’s sound. The downside of tube transmitters is the delicate tuning procedure to reduce the AM noise. High-powered transmitter tubes are also getting more expensive and, for some types, harder to source.
These connectors appear on the backs of various FM and lower-power TV transmitters. I thought it would be interesting to explore them a little bit.
First, according to Wikipedia, DIN is an abbreviation for Deutsches Institut für Normung. If you enjoy a lager or two then squint at that name you might see The German Institute for Standardization. 7 is the size of the inner conductor contact in mm and 16 is the size of the inside diameter in mm of the outer conductor. The thread is 29 x 1.5 mm.
From what I can find, the connector was originally developed for the German Military, which needed a rugged, efficient connector that was easy to install properly.
This style of connector is very popular with cellular antenna manufacturers due to its relatively high power handling capability and excellent passive intermodulation performance.
According to Amphenol, their 7/16 DIN connectors have the power handling capability of 3000 watts/1 GHz @ 25C (77F). That is a fairly low temperature. They give the working voltage as 500 V RMS continuous, which is 5000 watts at 50 ohms impedance. That, of course, assumes a 1:1 match, which is never the case. The connector is probably safe to ~2 KW in normal operating conditions for VHF and UHF TV operation.
Amphenol 7/16 plug for LMR-400 and Belden 9913
Also, keep in mind that RG-8, RG-213, RG-214, LMR-400, and Belden 9913 look similar but they use different connectors because the inner conductor of the latter two is larger than RG-8, RG-213, or RG-214. This happened on a project recently. It came time to crimp the pin on the center conductor and, oh no! The pin was too small!
A properly installed connector will be outdoor water-resistant in most weather conditions.
I finished up another GatesAir FLX-10 install recently. This one was way out in Provincetown, MA at the end of Cape Cod for WOMR (Outer Most Reaches). That is a community radio station that has an eclectic mix of programs. The studios are on the second floor of an old church.
Main studio, Wheatstone ConsoleTalk Studio, up/down studio furniture
The transmitter site is located about a mile away from the studios.
WOMR antenna
A few details on the installation; the antenna is mounted on the water tank, which is the tallest thing around for many miles.
WOMR antenna, Shively 2 bay 6810 mounted on a water tank
The building is less than 120 square feet, which made working a little tight.
WOMR transmitter building, Provincetown, MAGatesAir FLX-10 transmitter placedPump Station
There was very little room outside for the heat exchanger because of the need to get vehicles around the water tank for maintenance. The area around the building was taken up with a generator and HVAC gear. We ended up mounting it to the side of the building horizontally. The main reason was that the wind at this location could come from any direction. If mounted vertically, there was a chance that the wind could blow into the heat exchanger against the fans, possibly causing some overheating problems. Also, the horizontally mounted unit will have a smaller surface area during Hurricanes and Nor’easters.
Heat Exchanger, mounted horizontally on the northeast-facing wall
To do this, I made a unistrut frame and attached it to the outside wall.
The liquid-cooled transmitter takes up much less floor space than the prior transmitter, a Nautel V-10. This installation also included activating an HD Radio signal for this station.
The GatesAir FMXi4G importer/exporter resides at the transmitter site. Currently, the station has HD-1 on the air, no word on any future sub-channels.
Looking North towards the Atlantic Ocean
We had nice weather on one of the days. On the last day (Friday) it was raining with 35 MPH wind guests.
Speaking of Marconi, the US’s first trans-Atlantic wireless transmission station is a few miles down the road in South Wellfleet. Nothing is left of the site; time and erosion have taken all traces away.
Postcard, South Wellfleet Marconi StationBronze plaque placed in 1953 by the Wellfleet Historical Society
Here we are standing on the location of the transmitting building. The last two tower bases tumbled over the cliff edge in 2011.
It’s always an enjoyable time installing a liquid-cooled transmitter!
