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.
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.
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.
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.
In the rack room, the transmitters are combined into a Bext FDCSDC2 star point 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).
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.
That’s the second BEXT TFC2K to be put in Pittsfield in the last year.
I put one in at 104.3 down at the Eagle Building last spring, replacing an old Armstrong FMA antenna. I really liked the construction of the antenna, it feels much more sturdy than the Nicom counterpart. And for a location that isn’t exceptionally high off the ground, the signal is rather good. Much better than the previous antenna. It won’t be the last Bext I purchase, that is for sure.
That is good information, Mike. Once the translator moves to this site I will drive around with my Deva Broadcast Band Scanner and compare the two signals. I agree with you, the Bext antenna is better quality than the Nicom unit.
Did a NEC model of the Nicom version for someone (don’t remember who) a few years back. The pattern looks good in the model. Seems like a good general design.
That BeXT antenna looks like two 45 degree “V” dipoles mounted 90 degrees apart physically, both off-center fed (in phase?) a’la “Gamma Match”. Interesting way to get a circularly polarized signal. I’ll have to try building one for 2 meters sometime, as a kind of experiment. They do look stout, is that aluminum or stainless?
Bill, I’ll do an A/B comparison between this and the Shively in a later post.
Crusty, Your description is accurate, there is a transformer under the white cap, but I believe it is a power divider. The antenna is made from aluminum. This type of circularly polarized antenna works well for transmission but is inefficient for receiving.