We all get used to the idea of band conditions changing while listening on HF. The different bands are different by time of day or position of the sun, conditions make long, slow changes with the sunspot cycle or with the effects of solar weather. Aurora can upset the applecart of the time-of-day changes. Changes on HF frequencies are accepted as the norm and can come swiftly and suddenly.
Why is it, then, that it is difficult to imagine that happening on the medium frequencies? Is it because we are used to listening to them with the expectation that our usual, local stations will always be there? Because most of the time we are looking for something that is not DX, but something that is within groundwave range and dependable?
Sometimes, even those of us who have been digging out DX there for years have not noticed the day-to-day changes, chalking up hearing different stations on the same frequency to other factors, perhaps even using a loop or other form of directional antenna.
Truth be told, there can be tremendous differences from one day to the next, particularly during the grey hours of dusk and dawn. For me, this realization came about fifteen years ago when I began doing quick band scans while commuting to work. Because of the relatively short commute time ( not saying this to yank the chains of those with long drives each morning) of only about fifteen minutes in my previous job and less than ten minutes in my current one, I slipped into the habit of punching up a series of " regulars ". I had a list of a dozen and a half or so of stations that I would check in sequence while driving to work. It, thus, became easy to notice any sudden changes from day to day.
There were also the seasonal changes among these same stations as sunrise time changes throughout the year. These changes are gradual and through the year allow different signals to be heard on the same frequency as day light and darkness trade places from being east of me to west of me, or vice versa, as the seasons change.
But these seasonal changes are not what I am talking about. They are the sometimes wild differences from one day to the next at the same sun-time.
Sometimes they are measurable against a ground wave, or semi-local station. An example of this for me is WTAW in College Station, Texas on 1620 kHz. Even though this station is 90 miles away, even on its night time power of 1 kw it is audible here in Waco on the radio in my 1999 Ford Ranger pickup. In the winter when I am driving to work maybe an hour before sunrise, Cuba is audible in the background. Some mornings it will be just audible in the background, but some mornings it will be blasting in almost enough to cover WTAW up completely. ( By the way for those wondering what a radio station in Texas is doing with a "W" prefix callsign, it was licensed in 1922 before the dividing line of the Mississippi split up "K's" to the west and "W's" to the east. The station has changed frequency several times since then)
The same can be said for watching what happens with KSKY, 660 in Dallas, 90 miles in the other direction. On their reduced nighttime power, they are marginally audible even at night, but some mornings or nights other stations cover them, others they don't. On this one, unlike WTAW where there is one dominant station that threatens to cover it, on 660, different stations may appear over them on different days, showing heightened prop in slightly different directions from one day to the next at the same sun time.
On other frequencies, skywave differences can be more dramatic. In the mornings, on 890 some mornings WLS from Chicago will dominate, while on others some station from Mexico will cover it. At night, it might even be a Cuban, depending on the band conditions.
In fact, the Chicago station "skyline" can offer some real comparisons. There are 50 kw stations that are capable of good signals into central Texas on 670, 720, 780, and 890. If prop is good from the north, they will all be audible. Other mornings, there may be stations either sharing the dial spot with them or completely covering them up. It is interesting to note that at sunrise, the lower frequency ones will disappear first, often with WLS on 890 being the only one " left standing" as the sun comes up.
The sunrise effect also shows up on the stations from Mexico as well, with the lower dial position stations such as 540, 730, 900, 940, 990 disappearing in that order while 1000, 1030, 1050 and 1060 and particularly 1570 still booming in even after the sun is fully up.
Sometimes the band just before sunrise will show what amounts to "directional" characteristics, with all of the Chicago stations coming in well and the western stations such as KHOW, KOA and KSL being below par. Some mornings it will be the opposite, even from one day to the next at the same sun time.
It must be cautioned that in all this comparison, signals of different stations on different frequencies not be compared directly to other stations on other frequencies because there can be notable differences in facilities, power, or directivity of transmitters. However, what can be noted is the relative difference between the signal strength of each station with what it appears to be on other days and noticing the different " amount of difference" between each when compared with itself.
For example, to show a difference in band conditions that is frequency dependent, one might note that the Chicago 780 station might be a tremendous difference ( say four of five s-units down in looking at a meter) while the 890 Chicago station might be only down three s-units from what it was the day before.
Or perhaps the 890 Chicago might be very low compared to the day before or even covered by Mexico while KSL Salt Lake on 1160 might be much stronger than it had been the day before at the same time.
Sometimes aurora can cause some really unusual effects, such as the more northern stations disappearing completely, leaving new or previously unheard stations from other directions in the clear.
On a drive-to-work day noticing is about all that can be done as there is really no time to tune around and check other frequencies. If one is home or otherwise has the time to tune around it might be different.
In any event, checking the "regulars" can be a clue whether its worth the effort to look around or spend the time doing something else, perhaps tuning around on HF.
For me here in Central Texas, there are several either/or frequencies to check. On 560, is it semi locaI in Beaumont or Denver? On 630 is it San Antonio or Denver. On 580 is it WIBW or XEMU?
Is there anything showing up behind KLIF Dallas on 570 or behind KTRH Houston on 740? On 940 is it Midland or Mexico City? You get the idea. If things are out of the ordinary, it might be time to fill up the coffee cup and dig in.
There is one other "beacon" I use here to determine how I spend my predawn time on the weekends. I tune up to 2850 khz and check on the strength of the 50 kw station in Pyongyang, North Korea.
Many might not even know such a station is even audible in the US. However,it can be counted on to at least be detectable almost every morning. Some mornings it will be very strong. If it is strong enough clearly hear speech and music, it is worth spending time to check for trans-Pacific stations on MWcoming through.
I am not sure how all DX-ers are fixed for time but I am sure most find other things that compete for their time. For me, it is a full time job, family, household chores, contract work and writing (do I write for this blog or play with the radios!!) For others, there are surely other things that vie for your attention. Sometimes a little scouting about may help you decide how the time available might be spent. Do you look for MW DX, tune up through the shortwave bands or if its really bad, give up and turn on the telly (nooooooooo!!!!)
Even on the bad days there are things the died-in-the-wool DX-er can do, but we can look at that another day. Until then, good listening!!!