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.
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.
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.
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.
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.
All of the cabinet interconnects; RF plumbing, grounding, AC supply, sample lines, and various control lines were completed.
Most of the harmonics (2-10) looked like this. However…
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.
Interesting! Any word on why they elected not to a liquid-cooled FLX? This would seem to be the ideal situation for it…
I really like how these Gates exciters sound. I’ve put a few in myself and am always impressed with their overall quality.
While I have heard the same thing about the area, when I was down there (I have some great shots of the tower…) I never once felt unsafe being out of the car, taking shots.
That hybrid looks familiar!
Just like the ones on the Dielectric combiner we have, but it’s the input and splits the RF into parallel bandpass cavities and the reject port.
Had one input with loose hardware that got quickly toasty. Mr. Eckmann came up with parts from a decommissioned combiner for us.
I would think that the transmitters would be vented to the outside.
If not, I would hope they have very good air conditioning.
WEZN here in CT runs a Fax 20 air-cooled we vent it outside using a fan power vent out through the roof the transmitter generates a fair amount of heat. Nice install Paul.
Many transmitter sites are in a bad section of town. The land is cheap and the zoning is easy. I remember when WXIA’s (TV) TT50FH transmitter was shot up. There was never a problem in that area before. They were off the air for a few days.
Pretty much all of the DC area class Bs are an easy catch up here in my part of south central PA, except that one, which I figure is due to it being about the only one with a transmitter site on the southeast side of the city, when basically everyone else is up on the north side. Plus having a grandfathered overpowered 95.5 to my west doesn’t help either, but when a good duct sets up between here and DC, that one usually booms in here.