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The FCC has concluded its spectrum auction, and although the winning bids generated only about ¼ of what was expected, plenty of TV stations will be moving to new channels.

But there’s a catch. And you probably won’t be happy when you hear about it.

Currently, the majority of TV stations broadcast in the UHF television spectrum from channels 14 to 51. Another smaller block of stations use the high band VHF channels (7 through 13) while fewer than 50 stations transmit on low band VHF channels (2 through 6).

That is certainly going to change, as it appears all UHF TV channels above 37 will be re-allocated for a variety of services, including Wi-Fi, mobile phones, and a bunch of other “white space” operations. There may even be a few TV stations still mixed in with these services, and we won’t know how broadcasters will be re-packed until early April.

Finding new channels for broadcasters who gave up their channels in return for some nice cash will be a pain in the neck. And it will certainly require some stations to move back to those low-band VHF channels, which were once desirable back in the early days of television (Channels 2 and 3 were ‘golden’ then), but now make up what’s essentially the low-rent district of TV broadcasting.

Why? First off, much larger antennas will be required to receive these stations. A full wavelength at 56 MHz (channel 2) is about 5.4 meters, or about 17.5 feet. So a somewhat-efficient ¼-wave whip antenna to pull in that channel needs to be about 4.4 feet long. (Now you know why grandpa and grandma’s TVs had those long ‘rabbit ear’ indoor antennas!)

That’s not to say you can’t pick up these channels with smaller antennas – if the signal is strong enough, you probably can. But that means being much closer to the transmitter than you’d need to be with a high-band VHF or UHF signal, as it’s easier to design antennas for those channel that have some gain.

Here’s another problem. The spectrum from 50 to 88 MHz is historically plagued with interference from impulse noise (vacuum cleaners, electric motors, switching power supplies, lightning and other static). And during certain times of the year, atmospheric enhancement of radio signals occurs where distant stations will come in stronger than local stations, creating plenty of interference (ionization of the E-layer of the troposphere, a/k/a “E-skip”).

While the high-band TV channels are also susceptible to man-made and natural interference, it’s not as much of a problem. And UHF TV signals are essentially immune to impulse noise, although they can also experience signal ‘skip’ conditions; particularly in the late summer and early fall with tropospheric ducting.

During one of my RF and wireless classes at InfoComm, we aimed an antenna from the 2nd floor North Hall meeting rooms toward Black Mountain, a line-of-sight path parallel to the Las Vegas Strip, to try and bring up channel 2 (KSNV). Guess what? We couldn’t even find the signal using a spectrum analyzer, due to all an extremely high noise floor of about -50 dBm. (The noise floor at my home office is about -88 dBm, which is moderately quiet.)

Reception of channel 2 became such a problem for KSNV that they eventually relocated to UHF channel 22, where they can easily be picked up with an indoor antenna. But other stations won’t be as fortunate, as the spectrum will be fully packed after this year with no place to move for a ‘do-over’ if reception is a problem.

When the DTV transition happened in June of 2009, three stations in Pennsylvania, New York, and Connecticut had to move to channel 6. It became apparent very quickly that DTV converter boxes weren’t selective enough to reject interference from nearby high-power FM broadcast stations. So WPVI in Philadelphia and WRGB in Schenectady applied for and got permission to double their transmitter power in hopes of fixing the problem.

WPVI’s signal on channel 6 is having a hard time up against the many Philly-area FM stations just higher in frequency.

You can see how much of a challenge this downward move will present to people using indoor antennas. Figure 1 shows how WPVI’s 8VSB carrier looked when I tested the Antennas Direct ClearStream Eclipse loop antenna with an amplifier, while Figure 2 shows channels 9 and 12 with the same rig – but a much lower noise floor. Note the strong FM stations immediately to the right of WPVI, a potential source of interference and receiver overload that would not be an issue on high-band VHF and UHF channels.

This view of WBPH-9 and WHYY-12 shows both carriers standing tall above the noise floor (about -85 dBm) and easy to receive.

Figure 3 shows a bunch of UHF channels received the same way – the Eclipse has some resonance at these frequencies as it is close to a full-wave loop antenna, so indoor reception is relatively easy.

Pulling in UHF TV stations is a much easier task for a small indoor antennas like the Eclipse. A low noise floor (-87 dBm) doesn’t hurt, either.

I have two pretty sophisticated rooftop antenna systems (one on a rotator) and I have trouble picking up KJWP-TV in Philadelphia on channel 2 – the signal breaks up frequently and there’s lots of broadband noise showing on my spectrum analyzer when I point the antenna in that direction. There’s also a station on channel 4 (WACP) that pops in from time to time, although in the other direction toward New York City.

If a station you like to watch has to relocate to the low-rent district, you may need to spring for a better antenna, and it might be larger than some of the indoor models you’re used to seeing. If you are 20 or more miles away from the transmitter, you can forget those small picture frame or box-shaped models – they won’t work.

You might even have to (“gasp!) go back to using a pair of rabbit ears. Yes, they still make these; I found a pair in Best Buy the other day for about $15. Or it might be time to consider an outside antenna, and even that will have to be larger.

I’ll have more news once the spectrum repack is done later this month, and the FCC usually provides a link to a listing of TV station channel assignments. If you live near a large city where most of the high-band and low UHF channels are Being used by major networks, you’re probably not going to see much in the way of musical channels.

But if you live in a market where all of the active channels are on UHF – say, like Syracuse, NY or Scranton/Wilkes-Barre, PA – don’t be surprised when you can’t pick up some of those stations in the future. They might have moved down the street…

 

 

 

The post Broadcast TV Spectrum Repacking: The Devil Is In The Details appeared first on HDTVexpert.

Posted by Pete Putman, March 13, 2017 10:43 AM

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About Pete Putman

Peter Putman is the president of ROAM Consulting L.L.C. His company provides training, marketing communications, and product testing/development services to manufacturers, dealers, and end-users of displays, display interfaces, and related products.

Pete edits and publishes HDTVexpert.com, a Web blog focused on digital TV, HDTV, and display technologies. He is also a columnist for Pro AV magazine, the leading trade publication for commercial AV systems integrators.