Is it just me or can radio signals travel further at nite? I noticed as we were traveling cross country that i would loose my favorite local station within 100 miles or less during the day but at times out in the deserts at nite we could pick it up again. Can someone please explain?
There’s a good explanation here: http://www.alfenterprises.com/receivers/shortwave/shortwave_101.htm
That link mentions the F layer of the ionosphere, but not the Heaviside (E) layer, which also reflects some EM waves. Here’s a bit on how the solar wind pushes the E layer down during the daytime and thus limits the reception of distant stations.
In addition to the way signals bounce through the atmosphere, you’ve also got less interference from the sun at night which allows your radio to pick up weaker signals.
Also, while many stations have to reduce their power at night, some stations are permitted to actually increase their power at night. Other stations may not change power, but may change the directionality of their antenna at night. I know of a country radio station in west virginia that broadcasts in a fairly uniform pattern during the day, but goes to a more directional antenna at night, aimed (oddly enough) towards canada. They get plenty of canadians showing up for the country music festivals, so I guess it works.
I assume you are talking about WWVA, 1170 kilohertz in Wheeling. Under the old Clear Channel designations, WWVA and KVOO in Tulsa, Oklahoma were assigned equal standing on this frequency, i.e. both were “Class I-B” stations. So, at night, WWVA sends most of its signal to the northeast to avoid interfering with KVOO, conversely, most of KVOO’s nightime signal is sent toward the southwest to avoid interfering with WWVA.
Without getting too technical about it, Radio Engineering Handbook by F.E. Terman states that it is mainly the E layer that absorbs the transmitting antenna sky wave in the daytime. The received signal in the daytime is entirely composed of the ground wave component of the total transmitted power, the sky wave being rapidly absorbed by the E layer. At night the E layer lifts allowing the sky wave to be propagated and greatly increasing the area that is covered by the station. I have received WHO Des Moines here on the California desert and that’s about 1500 air miles distance.
And for you Iowans, I meant the old AM radio station WHO and not WHOTV.