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The Other Antenna
Trends in Technology usually covers new technologies and how to make use of them in our broadcast facilities. Still, it's worthwhile upon occasion to look at more common technologies to see what the most up-to-date products are and how they relate to common applications. This article is about antennas we don't commonly think of for broadcast transmission.
Application 1: off-air reception
There are many reasons you may need to improve or otherwise change off-air reception at your studio facility: Perhaps you've been made into a cluster with another transmitter site in a different direction; perhaps you are assembling a new facility all together; or perhaps you want to add something as simple as TV reception. (After all, what jock doesn't like TV in the studio?)
The best kind of receive antenna for off-air reception is one with good directionality and some amount of gain. The reasons are simple: mitigation of multipath. The directional characteristics of most yagi-type or log-periodic types of antennas have very high front-to-side ratios and front-to-back ratios. This means they effectively reject signals that intercept that antenna from its side or back. When you orient this type of antenna at your transmitter site, you emphasize the signal coming from that direction, while de-emphasizing signals coming from all other directions — and that includes multi-path reflections.
Probably the most well-known manufacturer of antennas for this application is Kathrein/Scala. If you have the space and a strong enough mount on the top of your building then you may want to consider the CLFM, which is a log-periodic covering the entire FM band with 7dB of gain over a dipole, and a front-to-back ration of 25dB (front to side even higher). It comes in 50Ω and 75Ω versions, and can be mounted in either horizontal or vertical polarity. If space is a consideration you may want to go with the YA7-FM instead. This antenna has the same gain as the CLFM but not nearly as good of a front-to-back or front-to-side ration. The YA-7FM can also be mounted in either polarity.
For off-air TV reception you may also want to consider Kathrein/Scala. For low-band VHF, consider the CL-26HCM (channels 2 through 6); the HDCA-10 (channels 2 through 13) or the CL-1469 for the entire UHF band.
After you install the antenna and orient it correctly the last thing you want to do is to run low-quality coax to the receiver(s). By low-quality I mean cable with excessive loss and/or poor shielding characteristics. (Remember this is a critical application that will hopefully only be installed once and provide years of service.) One possibility is Belden 1694A. This is for 75Ω applications, and you would need to choose the black (PVC) jacket for outdoor applications. Another possibility is from a company you should know about if you don't already: Times Microwave. Its cable for this application would be LMR-400-75. Both of these cables exhibit low-loss and better than 90dB of shielding.
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