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Re: WJIB at night

What you're talking about here is groundwave reception, 
which doesn't normally change much as a function of 
atmospheric conditions--although long rainy spells or 
long dry spells affect soil conductivity, which affects 
groundwave reception.

But WUNR being totally lost on the north shore at night 
IS a skywave phenomenon. The signal that you couldn't 
get from WUNR is presumably groundwave, but the 
interfering signals from WWRL and other stations, which 
drown out WUNR at night, are skywave, and skywave 
reception is extrmely sensitive to atmospheric 
conditions. The better the skywave reception on any 
given night, the more likely a station like WUNR, which 
doesn't put all that strong a signal into the north 
shore, will be drowned out where you were listening.

WUNR uses towers that are greater than half-wave. Such 
towers do put an upward lobe into the vertical-radiation 
pattern that can cause the station's own skywave to 
interfere with its groundwave. In WUNR's case, though, 
that effect shouldn't be noticeable on most nights 
because the interfering co-channel skywaves decimate the 
groundwave much closer to the transmitter than the 
points at which the station's own skywave interferes.

WUNR's interference-free night contour is about 5 mV/m. 
This is the contour at which the root-sum-squared of the 
two or three strongest 10% skywaves is 1/20 of WUNR's 
groundwave. In other words, the RSS of the strongest 10% 
skywaves is supposed to be about 0.25 mV/m, which sounds 
to me like an extremely optimisitc value for 1600 in 
these parts.
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> Last night (5/25) I was driving in West Peabody (MA) flipping through the AM 
> band and caught WJIB at about 930pm. I thought WJIB had a blistering 5w of 
> power...how can a signal carry that far at that power? It wasn't great, but it 
> was listenable. This was a stock Delco radio in a Lumina-and the engine was 
> running! Was this a fluke? I had it maybe 3 miles, and lost it on 128.
> WCCM (800,Lawrence) was very listenable at their 203 watts, too-and it's 
> usually not there at all. But, 5000 watt WUNR (1600,Brookline) was totally 
> lost.
> Can AM reception vary due to atmospherics?