Radio Propagation and Unexpected Loss of Signal?

Steven Wallace asks: "I'm currently attending an Internet2 related meeting (Joint Techs) in Boulder Co at the NIST building (same building as the most accurate atomic clock). WWV, the radio station that broadcasts the current time on 2.5, 5, 10, & 15Mhz is just down the road in Fort Collins Co. They transmit with about 50,000 watts. Surprisingly I can't receive any of the WWV broadcasts while here in Boulder (I carry a sony shortwave radio with me). The locals tell me that Boulder is a dead spot. I would think I'd hear the thing in my filings given the proximity and power. Anyone care to explain the radio propagation physics that prevent me hearing WWV while at NIST?"

Comments

Reasons?

[Jonny 290]

There are two possibilities here.

Case A: Your receiver's front end is overloaded with the strong signal. Extremely strong transmitters will induce large voltages in receiver circuits that have automatic gain control circuits and 'fake them' into believing that the station they're listening to is extremely strong. That, or the front end amp simply can't handle the (relatively) large voltage coming in and it's just thrashing everything.

Case B: Skywave vs. ground-wave propagation. Radio signals from 1-50 MHz often bounce from earth to ionosphere and back, and often several times to get to your radio. That signal may be not propagating well via ground-wave to your current location, and the skywaves are effectively bouncing right over your head.

Here are a few links to get you started:

Realtime HF propagation news from qsl.net
Lots of info on propagation effects