10 Nights of Medium Wave Propagation

For 10 nights in late January and early February I recorded the carrier strengths of eight medium wave broadcasts from transmitters in western Canada and the western US.

Here is an example showing the individual signals from a single night...

Since top end of the medium wave broadcast band is more than three times higher in frequency than the low end of the band and since the band spans the electron gyrofrequency range, I thought it would be worth dividing the frequencies into "low band" (below 700 kHz), "mid band" (near 1,000 kHz), "high band" (above 1,400 kHz) ranges...

Here are what the same looked like two days later...

It's probably worth noting that the mid-band curves are averaged over only two signals, commpared to the low-band and high-band curves which are each derived from three signals, so it should be more variable. The mid-band signals also happen to be from transmitters to the west of here while the others are from the south or near southwest.

To get a better idea of what to expect on a typical night, this next graph shows averages over the entire 10-day period...

The high-band curve is higher because one of it's three component signals is quite a bit stronger than the others. Not surprisingly, the shape of the low-band curve is the one that most closely resembles the NDB curves of my previous longwave post.

Since KSFG and KFBK both serve the Sacramento, CA area (almost identical distance and direction from here) and are both near the top end of the MW band, I singled them out for closer examination...

I am not quite willing to interpret the dusk and dawn peaks at either end of the KSFG curves as greyline enhancements because they are only based on 10 nights and because similar features do not show up on any of the other curves from the same nights.

UPDATE REGARDING THAT LAST POINT: Two local friends (Thanks Walt, Hew.) have pointed out that those KSFG peaks could easily be explained by the switch between day and night power at those times.