I’m not sure if I’m noticing over time, a steady decrease in the propagation characteristics of the AM radio band, particularly those frequencies above 1 Mhz, or a steady degradation of the performance of my AM receivers and a lack of quality in newer receivers.
I live in Shoreline, WA, just north of Seattle (about 13 miles north of downtown Seattle). I used to be able to receive CFUN in Vancouver, BC, Canada, about 100 miles to the north, at about S8 on my receivers that had an S-meter and strong enough, save for the occasional night time fade, to be listenable.
For the last few years though, CFUN barely comes in at all, not even S2 on the S-meter anymore and the noise level is too high to tolerate listening, even at times to be intelligible. Even many local stations which used to be solid are now marginal, particularly on the high end of the band.
At the same time AM propagation seems to have suffered, the higher shortwave bands seem to be alive at times of the year and times of the day that they wouldn’t have been in the past and sporadic E-skip on the low VHF TV channels has almost become so regular that calling it “sporadic” anymore seems inappropriate. It seems to occur more frequently now during the winter months during a solar minimum than it used to during a solar maximum in the summer. And during the last solar maximum, on one occasion I got skip all the way up to channel 10, and for all I know it may have gone past that but there are local stations on 11, 12, and 13 that would have required a very strong signal to overrun.
I’m wondering if this is the result of changing atmospheric chemistry, or a general increase in RF power levels causing an increase in ionization, or HAARP, or some other factor(s).
I think it’s the sun spot cycle.
Things change constantly. Keep using your loop antennas.
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I’m familiar with sunspot cycles. I’m 49 years old; I got my 1st phone in my junior year of high school, I’ve had shortwave receives since I was in elementary school. This is not something new to me.
There is a sunspot cycle, the full cycle is 22 years long with peaks every 11 years (the Sun’s magnetic field reverses polarity each 11 years so that a total cycle takes 22 years but peaks are 11 years apart, on average).
During peak years, it is normal for the maximum usable frequency to be higher, 9Mhz+ in the winter, sometimes reaching up as high as 18 Mhz or so (not counting Sporadic E skip which may reach up into the 200 Mhz range).
In the summer during peak years the tendency is for the MUF to be higher (at our latitude).
But during Solar minimum, in the winter, at night, usually not much above about 6Mhz, and here we are right now I’m listening to a signal on 9484 Khz (9.484 Mhz) and it’s not a marginal signal either.
At the same time the MUF increases, absorption on lower frequencies increases. During a solar minimum, AM night time propagation used to be excellent, now it’s marginal.
Over the years, there has been a steady upward trend in MUF, across the entire solar cycle, and it would seem in AM absorption although the elimination of clear channels really makes that hard to test since there is so much co-channel interference now.
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