Digital TV Reception Difficulties

By: Tom Weeden, WMTV/NBC15 Chief Engineer Email
By: Tom Weeden, WMTV/NBC15 Chief Engineer Email

Posted Monday, August 5, 2013 --- 3:43 p.m.

We recently had a request on Twitter (@WMTVtech) to explain why reception is so poor most mornings. For the roughly 15% of viewers who use an antenna for local TV reception, sometimes there are conditions that adversely affect how our signal arrives at the home TV set.

Reception performance depends mostly on what type of antenna is used and where it's located. Generally, a TV antenna mounted on a roof or a tower will receive signals better than an indoor antenna. The amount of signal received also depends on how far a viewer is located from the TV station's tower and what kind of terrain is between the station and the viewer that could potentially block signals.

To some extent, weather conditions can affect TV reception. The most common weather-related issue is an atmospheric inversion, which allows TV signals to follow the curvature of the earth instead of going in a straight line off into space. A typical full-power TV station will have a range of about 60 miles under normal weather conditions, but during an inversion, signals can travel hundreds of miles. When a broadcast from a distant station on the same channel as the one you're trying to watch is strong enough, it can cause your TV set to lose reception of the local station.

When the FCC allocated a digital channel to each full-power analog TV station in 1997, there were some "short-spacings" made so that they could all fit. WMTV's digital channel is now 19 (which your TV still displays as 15.1 thanks to the electronic program guide signal we send). We are close to WGN in Chicago, a mere 124.5 miles away, both of us on channel 19. Back when we were on channel 15, the nearest TV station was in Austin, MN at about 156 miles. That was a little more breathing room. And while analog interference was merely annoying, digital interference causes reception to just quit with your TV usually displaying "Weak signal."

Most of our viewer reception calls have been from Reedsburg, Baraboo, Wisconsin Dells, Mauston and Montello. TV antennas in those locations aimed at Madison can also favor Chicago when conditions are right.

As far as other Madison stations go, WKOW-TV, formerly channel 27, is now digital 26. The closest station on 26 to them is WBBM-TV in Chicago, at 119.4 miles, which is a bit closer than the spacing we have with WGN. Fortunately for WKOW, WBBM runs fairly low power, so interference from Chicago on channel 26 is minimal.

WISC-TV, the old channel 3, is now on channel 50. Their nearest neighbor is WFXT in Aurora, IL at 126.6 miles. That's also a bit close for comfort, but WISC was assigned a higher power level and so probably wins the interference wars more often than we do.

WMSN, "Fox 47," is now on digital channel 49. KLJB in Davenport, IA is only 127.9 miles from WMSN.

WHA-TV, Wisconsin Public Television was on channel 21 and now is on 20. KSMQ-TV in Austin, MN provides a little more separation on channel 20 at 156.1 miles. KSMQ was the aforementioned analog station on channel 15 that used to cause us some interference before we all changed channels.

And the winner for elbow room is WBUW, analog 57, and now digital channel 32. Scanning the FCC database for the nearest channel 32 full-power station gives us WCCO-TV Minneapolis/St. Paul, 228.8 miles as the crow flies.

The summertime "skip" season is here, so if your reception is sitting right on the edge of the digital cliff, you might see patterns based on weather conditions, especially early in the morning and late evening.

Click HERE for a zoom-able Google coverage map for over-the-air reception of NBC15 under normal conditions.

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