TopBand: Re: YB0ARA/9 and SUNRISE EFFECTS

[T A RUSSELL]

On Thu, 26 Mar 1998 11:12:30 -0500 "James S. Danehy" <w9vne@fuse.net>
writes:
>Scott Long wrote:
>> 
>>YB0ARA/9 had a nice signal again this morning, running about 449 here 
>>in Central Ohio.  Strange how this band works, yesterday morning I 
>>heard W8JI  (in Georgia)
>> working him, but he was not even as much as ESP here, and now this 
>morning  he was good copy with some QSB.  
>
>snip<
>
>That would indicate to me that the Terminator is giving us the 
>propagation to Phil. That would mean that it is coming from the east.
(NOT!)
>Could someone please explain that for me ? Is Phil's signal coming out 
>of the south and up the Terminator ? What does the Equator have to do 
>wiht propagating his signal ?
>
>snip<
>
>Jim W9VNE
>Cincinnati
>

There are TWO effects which take place at sunrise and sunset.

GRAYLINE effects refer to locations along the terminator, encircling the
globe
along a great circle route.  The GRAYLINE provides a low loss path of
varying
width and duration depending on frequency.  On 160 and 80 meters, these 
openings may last only a few minutes (and are NEVER shown on computer
predictions to my knowledge).  At the other end of the spectrum, there
are
also LP openings along the terminator on 10, 12, and 15 meters.

SUNRISE  ENHANCEMENT accounts for the peak associated with signals
coming from the westerly directions, NOT on the GRAYLINE but often
mistakenly
refered to as grayline.  This appears to be a focusing effect resulting
from
refractions from the normal  F layer propagation plus another refraction
from
the E-layer which combine to produce significant gains (on the order of 6
to 10 dB, sometimes even more) ranging from a few minutes on 160 meters,
10 to 20 minutes on 80 meters, and 30 to 60 minutes on 40 meters.  These
enhancements always occur AFTER sunrise on 40 and 80 meters and tend
to occur at sunrise +/- a few minutes on 160 meters.

SUNSET  ENHANCEMENT accounts for the peak associated with signals
coming from the easterly directions, NOT on the GRAYLINE.  Again, this
appears to be a combined F and E layer condition, occuring BEFORE 
sunset with durations similar to those of the above mentioned SUNRISE 
enhancement.

It is my OPINION that most computerized propagation programs DO NOT
account for the SUNRISE and SUNSET effects on the LOW  BANDS, which 
REQUIRE the presense of daylight at one end of the path to produce the 
signal enhancement.  I recall years ago there was a propagation column 
in Ham Radio Magazine in which the author ALWAYS indicated that signals
on the low bands peaked BEFORE  SUNRISE  ( NOT ! )  which told me he
had never listened to the low bands during his pre and post sunrise
times!

On 80 and 40 meters, signals ALWAYS peak AFTER  SUNRISE to the west
and BEFORE  SUNSET  to the EAST.   On 160M, signals can peak at sunrise
and sunset and can also peak during darkness.  160M is the LEAST
predictable
band in the amateur spectrum.

To my mind, most computer propagation programs are USELESS for predicting
optimum times for LOW  BAND propagation, especially the Sunrise and
Sunset
enhancements.  One recent SE  Asia DXpedition utilized such programs and 
regularly appeared on low bands between 10 and 12 GMT, BEFORE  USA
sunrise, and predictably worked few eastern USA stations, promptly
leaving the low
bands at east coast sunrise when their neighbors in DU, HS, 9M2 appeared 
with good signals into the eastern USA between 12 and 13 GMT.  (Just
because
someone is a good operator, experienced DXpeditioner, and uses computer
propagation predictions does NOT mean they will be productive LOW  BAND
providers on the difficult POLAR PATHS.   Dedication and experience is 
required.  The BEST example is the German team from VK9CR, VK9XY, S21XX,
ZL7DK, P29VXX.)

Again, in my OPINION, most computer propagation programs UNDERESTIMATE
MUF by a significant percentage.  IONCAP will often predict the MUF to
Europe
to be just above 21 MHz and yet we find 12 and even 10 meter openings. 
These
predictions are useful for indicating peak TIMES on the HIGH BANDS and
when
the HIGH  BANDS will open an
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d close (i.e. they pretty well know when the
sun
comes up and goes down) and their MUF numbers at least track actual MUF
even if they are not very accurate.  As you can tell, I am not a big fan
of computer
predictions.

The BEST tools for the serious LOW  BAND  DXer include a good mapping 
program (The DX  EDGE, GEOCLOCK, MiniProp by W6EL,  etc.) and/or 
accurate tables indicating SUNRISE and SUNSET.  It should be noted that 
the definition of SUNSET and SUNRISE is when the CENTER of the sun is 
at the horizon  (NOT first light or last light).

Remember,  it  takes a little LIGHT for the low band enhancements to 
materialize!

de  Tom  N4KG



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