The Bext TFC2K broadband FM antenna

FM Broadband antennas are a compromise because they generally have less gain than tuned antennas, are more complicated, and take up more space. However, this antenna has none of those issues. The gain and radiation pattern appears to be almost the same as a tuned three-bay FM antenna.

We are finishing up an antenna project in Pittsfield, MA, this week.

Proposed W277CJ 60 dBu contour
Remnants of Shively 6812 4-bay antenna

The project involved replacing a Shively 6812 tuned to 95.9 MHz (WBEC-FM) with the TFC2K so that the W277CJ 103.3 MHz (WUPE) translator located on the roof of the 14-story Holiday Inn on West Street could be moved to the studio location. In this case, having the translator in-house will save significant rent. The new antenna will continue to serve as a backup facility for WBEC-FM when the main site is off the air for whatever reason.

Single bay, Bext TFC2K antenna

The input power per bay is based on the antenna’s input connector. In this case, each bay has a 7-16 DIN connector and the power divider is a 7/8 inch EIA flange. Thus the maximum input power for this setup is 5.5 KW. The licensed output for both facilities is far below that.

3 Bays leg mounted on the tower

According to the manual, this antenna should be spaced at 0.85 wavelength, which is frequency-dependent. I chose a frequency halfway between the two (103.3 – 95.9)/2+95.9 = 99.5 MHz. The formula from the Bext general antenna manual is:

D = (300/F) x 0.85

Where
D = the distance between center of radiating elements (booms)
F - Frequency in Mhz.

Thus, D = (300/99.5) x 0.85 = 2.56 meters (or 8′ 5″)

As this is a series excited AM tower, some type of broadband isolation coil is needed to cross the base insulator. This one is simply a large coil of 7/8 inch coax, likely with a capacitor across the outer conductor to create a resonant LC network.

To me, it looks like a water heater. Since the ground is frozen solid, we made a temporary stand. We will have to come back in the spring to create a permanent stand or perhaps a unistrut mount to the wall of the ATU building.

Kintronic ISO-88P-78EIA-4C

In the rack room, the transmitters are combined into a Bext FDCSDC2 star point combiner.

Antenna combiner

Broadband sweep shows a good match across the entire FM band. I will be interested to see how it performs with respect to the Shively single bay 6812 on the roof of the hotel (103.3 W277CJ).

Return loss, Bext TFC2K 3 bay FM antenna

The return loss looks good on both 95.9 and 103.3 MHz. The interference noted in the sweep is from local FM stations including the main transmitter for 95.9 MHz.

Baltimore Public Radio gets a new FLX20

Another liquid-cooled GatesAir transmitter installation was completed for WYPR, Baltimore, MD. This unit replaced a Continental 816 which had a long life.

The area around the transmitter site is not the best neighborhood. The building was formerly the WBAL-TV transmitter site and was built circa 1947.

WYPR transmitter site
Original four-legged Blaw Knox self-supporting tower from the WBAL-TV days
Pump station and HTF tubing
Wall-mounted heat exchanger
FLX-20 transmitter

The transmitter room is a little tight, so it was difficult to get a good shot of the front of the unit.

The station is running HD Radio with -10 dBc.

This site has a strange 3-phase delta AC power configuration. The middle leg is at ground potential, and the other legs all measure 240 VAC to ground. I’ve never encountered that before. This is known as a corner grounded Delta, which gets rid of the high leg associated with most closed 3-phase delta systems.

Ultimately, all the leg-to-leg measurements are 240 volts, so the power supplies are satisfied. With these transmitters, the phase rotation does not matter because there are no actual 3-phase loads in the transmitter.

Inventory control, Home Depot Reisterstown Road, Baltimore, MD

The sign says “Free Tools.”

Installing a 60 KW FM transmitter

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 site
FAX60HD 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 transmitters
FAX60HD, WPGC-FM Washington
4 Inch Dielectric coax switch with 60 KW load
WPGC 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.

Marconi would be impressed

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 Console
Talk 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, MA
GatesAir FLX-10 transmitter placed
Pump 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 Station
Bronze 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!