Propagation 101

["Kaimbridge M. GoldChild" <kaimbridge@my-dejanews.com>]

With the "skip" and "tropo" season underway, this would be a good time
for a "brief course" on propagation.

     Frequency-MHz        Mode/Assignment
     =============        ===============
      0.550-1.700           MW
      2.000-30              SW
     26.965-27.405    (SW-VHF): CB Ch.s 1-40 (Ch.6 = 27.025)
         30-50      VHF-lo PSB (Public Safety Band: Police, fire, etc.)
         54-88       VHF-lo TV:  2-6  (87.75 = Ch.6 audio)
       88.1-107.9           FM
        174-216      VHF-hi TV:  7-13
        470-800         UHF TV: 14-69 (14-20 = 470-512 = PSB)

     "Tropo": VHF-UHF
     ================
Tropospheric enhancement, scatter, ducting, etc., is weather induced,
with distance range from semi-local enhancement (e.g., Cape and RI
coming in to Boston unusually strong) to central and southern ME and/or
western MA and CT, to bona fide NYC and Philly openings, to major events
(Canadian Maritimes to the north and the DelMarVA Peninsula to the
south).
In this area, almost all notable activity is coastal moisture related
(mostly fair weather fog banks and wind flow inducing "high pressure"
areas--the location of the high generally being where the stations will
be rolling in from <e.g., ME for tropo from the north and the Long
Island Sound to NJ for the south>), with the Grand Daddy Events usually
being caused by tropical storms and hurricanes (when around the
Carolinas is usually the jackpot for us).  The best time for tropo
activity is from evening to early morning.

     "E-skip": 27-108 (rarely up to VHF-hi)
     ======================================
Sporadic-E is the spring/summer event being mentioned recently in B-R-I.
It is a strictly VHF event, starting at the lower end (CB-Ch.6-27.025 is
a good "heads-up" frequency to check--listen for the midwest, KY, VA,
the Carolinas, GA and FL) and working up into TV-Ch.s 2-6, commonly
poking into the FM band.
It is an ionospheric event (originating in the "E" layer, thus "E-skip")
caused by the summer Sun (but NOT--directly, anyways--"sunspots"),
thunderstorm activity and certain solar/geomagnetic activity (sometimes
caused by sunspots and resulting in "auroras"), with a "skip" distance
ranging from about 500-1500 miles or more (for "double hops")--e.g.,
WEDU-3 FL is probably *THE* E-skip "pest" around here (with WESH-2 FL a
close second).  The E-skip season is pretty much May-Aug, with a few
openings usually noted between Thanksgiving and New Years (spill over
from the southern hemisphere's "summer season"?)--though an opening can
happen at any time of the year.  As for time of day, again, it can
happen at any time (some events last a day or more), with the prime time
being 9-noon-ish and again around 7-9pm.
A subcategory of E-skip is "meteor scatter", which is isolated E-skip
"blips" (though some can last a minute or more and *can* reach all the
way up to UHF), caused by meteors.

     "F-skip": SW (poking into VHF during solar cycle peak--like now)
     ================================================================
Strictly a daytime occurrence, it regularly visits the CB band during
the solar peak (check CB-Ch.6-27.025 for LA, TX, OK and even out to CA
and WA!), even reaching VHF-lo (e.g., local CA PDs, or even South
Africa, on 35-45 MHz!).

     "Auroral": VHF-UHF
     ==================
Sometimes morphing as an "E-skip" event, this happening is caused by
auroras, where the signals are peaked by aiming to the north (regardless
of the station's location) and is generally unusable, usually seen as
"hash" and heard as a weak (garbled?) signal mixed in the noise floor.

     "MW Skywave": MW
     ================
The skywave is always present--even during the day--but the reflected
signal is absorbed during the day and *during geomagnetic storms* by an
enhanced "D" layer, causing a blanketing (thus, in the winter when the
Sun isn't strong, some skywave bounce can make it through, even at
midday).  While there is no definitive "season", the shorter days/longer
nights tends to give winter the edge.  Sometimes at the onset of
geomagnetic storms, "auroral" type conditions will occur, resulting in
signal "wowing" and phasing (like you are hearing it from under
water)--locally, WTIC-1.080 Hartford seems to be one of the first
stations to experience this effect, when it occurs--followed later by a
deadening of the band.  During the height of the solar cycle (such as
now), even when there is no apparent geomagnetic activity, the MW band
tends to be dampened more often than not, especially at the lower end of
the dial (thus WSM-0.650, WSB-0.750 and even WFAN-0.660 may appear gone,
but WBAL-1.090, WWVA-1.170 and WQEW-1.560 may still be in full
strength).

This is by no means a thorough discussion of the matter, but should help
the casual dial surfers in B-R-I make sense of what they're hearing and
why.

Class dismissed.     P=)   P=)   P=)

     ~Kaimbridge~

------------------------------