Here is what I have been noticing. During the day, I can reach as many as 4 bars of signal strength on my Samsung 46" display. However, invariably, at night I lose the signal completely. Then, the next day,when it gets light, it's back! Granted I am at the fringe of reception (SW Mi, 66 miles from Chicago 26.1) but I do have a 40' tower, Winegard Yagi antenna, and amplifier. If the station is maintaining power, what if any atmospheric conditions occur to cause this?

What you are seeing is a propagation effect. Stations do not reduced power at night or any other time except during the rare time before a partial equiptment failure is fixed.
john

reducing power at night is not legal to do under FCC rules.

Here is what I have been noticing. During the day, I can reach as many as 4 bars of signal strength on my Samsung 46" display. However, invariably, at night I lose the signal completely. Then, the next day,when it gets light, it's back! Granted I am at the fringe of reception (SW Mi, 66 miles from Chicago 26.1) but I do have a 40' tower, Winegard Yagi antenna, and amplifier. If the station is maintaining power, what if any atmospheric conditions occur to cause this?

Seeing as you're talking specifically about 26-1, probably what you are seeing is interference from South Bend. Weigel, the parent company of WCIU and of WBND/WMYS/WCWW, operates a digital signal on 27 in South Bend in addition to the WCIU-DT signal on 27 in Chicago. My guess is that you are experiencing tropospheric ducting which is bringing the signal on 27 just strongly enough to damage the reception of WCIU.

- Trip

Here is what I have been noticing. During the day, I can reach as many as 4 bars of signal strength on my Samsung 46" display. However, invariably, at night I lose the signal completely. Then, the next day,when it gets light, it's back! Granted I am at the fringe of reception (SW Mi, 66 miles from Chicago 26.1) but I do have a 40' tower, Winegard Yagi antenna, and amplifier. If the station is maintaining power, what if any atmospheric conditions occur to cause this?

Only AM stations reduce power at night to decrease/eliminate interference to other stations on the frequency. This is not an issue with FM or TV stations due to the frequencies they operate at. What you are describing is a propagation issue being on the fringe of the coverage area.

I agree with Trip that you are probably seeing co-channel interference from another station that gets worse at night because of atmospheric conditions. I have a similar problem with WUNF-DT in Asheville NC which has its digital signal on ch 25. It's subject to interference from the analog signal of WOLO in Columbia SC which is also on ch 25. During the day, I get better reception on WUNF-DT because the signal from WOLO is relatively weak then. But at night, tropospheric enhancement kicks in, WOLO's signal increases here, and so does the interference with WUNF-DT. At least that's my theory. I'll know whether I'm correct next February when WOLO shuts down its analog signal.

And WUNF leaves channel 25 - that transmitter will be going to WUNC @ Chapel Hill.

Here is what I have been noticing. During the day, I can reach as many as 4 bars of signal strength on my Samsung 46" display. However, invariably, at night I lose the signal completely. Then, the next day,when it gets light, it's back! Granted I am at the fringe of reception (SW Mi, 66 miles from Chicago 26.1) but I do have a 40' tower, Winegard Yagi antenna, and amplifier. If the station is maintaining power, what if any atmospheric conditions occur to cause this?

You are seeing interference from analog WCCU-TV 27, which has a booming signal from north of Rantoul. People with analog sets can point antennas south and see channel 27 from the southwest and south suburbs. It propogates farther at night, and interferes with WCIU.

And WUNF leaves channel 25 - that transmitter will be going to WUNC @ Chapel Hill.

Not so. WUNU-DT is leaving channel 25 for 31. WUNF-DT is staying put.

- Trip