Sunday, October 11, 2015

Medium Wave Seasons Change

       We have now passed the Autumnal Equinox.  Days are getting shorter and nights are getting longer in the Northern Hemisphere,  with the opposite happening in the Southern Hemisphere. September 21-22 will mark the equal length days and nights.  The hours of grey line prop are changing and for some of us, the hours of optimum prop are shifting through our days.
       My time traveling to work is now right at sunrise local time. that means my "mobile DX targets" are becoming available again.  In the U-S where many  Medium Wave stations change power and directional antenna patterns between day and night interesting things can happen.
       While power and pattern change times are supposedly adjusted for the " worst case" interference possibilities, there is some averaging.  That means that toward the end of the months in which days are getting shorter, there will be some days when stations are still switching to daytime power while some night time prop is going on. That means the opportunity to hear some stations not usually heard.
       At the beginning of a month, there is also another opportunity brought about by errors.  Often stations are set up to change power and pattern by timer rather than human switching.  If, on the first of the month,  someone hasn't reset a timer, power change might come at the time set for the previous month and a few stations may end up on high power or day directional pattern while night prop characteristics are in place.  Sometimes if the duty of power and pattern change is left to a morning disk jockey or news announcer,  that person might forget about change times coming later and manually change early.  While this may result in fifteen minutes or a half hour interference to some stations, it will provide DX opportunities to the alert tuner of the dials.
       As these " new signals" appear on the band in the mornings, something else swill be noticed that might not be apparent while tuning the Medium Waves when it is already well dark.  Signals at the top of the band will be propping better than those at the bottom. One might not think that there would be that much difference for signals relatively close together in frequency,  but when one looks at the percentage of the bandwidth over the frequency itself,  the situation becomes more apparent. A 500 kHz spread in frequency over a band at 15 MHz might be only a small percentage but at 1 MHz ( or 1000 KHz) its quite a bit!  The D layer that does a lot of the absorbing at  MW frequencies is already starting to form,  and the frequencies at the bottom or even middle of the band are affected much more than those at the top.
       In my drive to work in the morning,  this is really apparent as the Chicago stations on 670,720,780 and 890 though all broadcasting non directionally with the same power are often of very different strengths.  The lower stations may be very weak as the sun is just rising, while 890 will be stronger.  Sometimes the lower ones are inaudible or even covered by other stations from Mexico that are in the same time zone or to the west of me.
       Stations from Mexico City provide another such "barometer".  Usually stations on 730, 900, 940,1000. 1030,1060 and 1220 from Mexico City are audible here. They are a bit to the East as well as being South of here.  Oftentimes the stations on 1000,1060 and 1220 are much stronger than 730 and 900 even though they actually run less power.  This situation is the reverse when the path is well in darkness.
       Other stations from Mexico show similar characteristics, though the comparison is not really as good because they are from different locations and are different distances. The 1050 ( XEG) from Monterrey will be much stronger than the 540 from San Luis Potosi. The 990 will be stronger than the 540 or 730. The 800 from Juarez ( XEROK) will be much stronger mainly because it is from the West of me by several hundred miles ( I am in Waco, Texas) while the 1570 ( XERF) is always the strongest of all, even an hour after sunrise while in the same time zone.  Of course, its is also the closest being just across the border from Del Rio.
       At sunrise, conditions seem to change very rapidly.  A station that is fairly well audible low on the dial when I leave the house at 1140 GMT might be taking heavy QRM hits or be fading down by the time I get to work at 1200 GMT. Stations high on the dial will still be fairly strong.
       Another thing I have noticed this time of the morning.  As the sun begins to creep over the horizon, skip on relatively nearby stations gets shorter. Stations like KMOX from St Louis-1120- will come up in strength,sometimes covering a new daytime station in the Austin area that has just signed on for the day. KWKH in Shreveport, Louisiana--1130--will come up above the Mexican station that sometimes dominates the frequency. KCTA in Corpus Christi on 1030 will come up over Mexico City's XEOY.
       Just as a note, KCTA is an interesting DX target. They are a Christian station that is day time non directional on 1030 KHz. However, because their dominant station, or the station they must protect, is WBZ in Boston, well to the east,  they get to sign on an hour before sunrise Central Time.  They also have a presunrise authority of around 250 watts.  A DX-er to the  West might have a good chance of logging them just before sunrise Texas time if he could null Mexico City.
       In addition to the changes as time passes through sunrise, there are also significant changes day to day due to other conditions.  In years past,  I had sort of assumed that prop in the Medium Wave band was pretty much stable day to day. This thought may have been somewhat reinforced by dealing with construction of stations and being aware of requirements for protection of other stations from interference at night.
       However, over the years I have noticed that such is not the case.  There can be considerable variance in signal strength from night to night, and particularly during the " grey "hours of dusk and dawn.
       It is one thing that I have enjoyed observing as I drive to work each day and even after over fifty years of DX-ing continue to learn.  At the same time on consecutive mornings,  the same station might have considerable different signals, particularly at the low end of the dial. For example, WIBW on 580 from Topeka, Kansas is a regular here just before sunrise.  Some mornings it comes in almost like a local station.  Yesterday, however,  it was almost covered by a Spanish speaking station. ( probably Piedras Negras) Once XEMU goes to daytime power, Topeka is gone. But with the border station on night power, WIBW usually makes it pretty well, though there can be exceptions.
       I have a couple of good barometers for enhanced prop.  Two stations from the Dallas area have relatively low power at night but have directional antenna systems that still deliver fair signals to the South and into Waco, KSKY on 660 and KAAM on 770.  A quick punch to those frequencies as I start the truck up in the morning ( I have preset buttons for them just for this purpose) will give a good indicator if something is up. If they are in with fairly clear signals,  I check the higher part of the band for DX.  However,  if they are being covered or have signals significantly causing them to "hop",  I know there is a chance of hearing something good down low in the band and I can spend the few minutes of driving DX hunting on that part of the dial.
       Other good "barometers" are 880 which is usually KVRN from Nebraska with some Mexican QRM and 980 which is usually Kansas City.
       The thing to note is that even the medium waves are not the same every day. Things can often change radically from day to day,  particularly if there is some kind of major solar activity.  Its worth checking your own "barometer" stations daily to get a clue if it worth checking for possible new logs.
       An example is the past couple of days ( October 9-11) when there was solar activity that totally mangled the upper HF bands but led to enhancement of MW and LW bands. here in Waco, Texas, a semi-local station ( WTAW 1620 in College Station, Texas 90 miles away) is usually audible day and night, though with some co-channel interference heard at night, usually from radio Rebelde in Cuba.  This past Friday night, Rebelde was propping in so strong it completely covered WTAW.  You could not even tell it was there! That led to tuning the rest of the band and logging a half dozen new stations.
       And finally,  I apologize for a lack of posts the past few weeks.  We have been making repairs to our home following a water pipe break that flooded part of the house, requiring a replacement of a wall and removing and replacing the flooring in the room where the radios and computer are located. Luckily none of the electronic equipment was damaged, but all had to be moved out and stored during the repairs.  Happily all is ( almost) back to normal now and hopefully at least weekly updates will be available from here out.  You are invited to scroll back through the archives.  Many articles are not time sensitive and hopefully will provide some entertainment if not useful information about a life behind the lighted dials!  Good DX.

1 comment:

  1. Glad to hear all has been repaired and back to normal.