[TowerTalk] Propagation / Beam Headings Responses

[n4kg@juno.com]

Sylvan,

Propagation prediction tools are useful IF you recognize their
limitations.

First, since they are based on AVERAGES, they typically
underestimate peak MUF.  If you are pushing the MUF limits,
it is wise to look for openings above that shown by the programs
at the TIMES when the programs show MUF peaking, i.e., if 
your program shows a peak MUF of 22 MHz, chances are good 
that 12M (24.9 MHz) may also be open on a good day, 
and perhaps even 10M (28 MHz).

Second, I have NEVER seen a propagation program that 
correctly predicts the enhancements seen on the Low Bands 
BEFORE SUNSET and AFTER  SUNRISE.  

Also, I have NEVER seen a propagation program which shows 
the SKEW Paths or Long Paths with skewing which thrill us with 
non-direct path openings to the opposiste side of the globe
around sunrise and sunset on 160, 80, 40, and 30M.

Propagation on 160M is very hard to predict.

Propagation peaks on 80M are VERY consistent, peaking
just BEFORE  SUNSET to the East and just AFTER SUNRISE
to the West, starting approximately 10 minutes after and lasting
until 30 minutes after, then dropping off for another 30 minutes.
(I have often listened to 3B8CF on 80M until 1 hour past his
sunrise).  Grayline peaks along the terminator can last from
just a few minutes up to 15 minutes bringing in those exotic
signals from SE Asia to Eastern and Central USA.

DX Propagation on 40M begins well before sunset to the East
and can last all night during medium to high sunspots.  In the
morning, signals to the Pacific and Asia peak 30 minutes after
sunrise and can last up to 3 hours past sunrise.  During LOW
sunspot activity, SE Asians can often be worked aiming SSW
along the terminator at sunrise.  This path is occassionally
open on 80 and even 160M with better than usual signal levels.

Note that Sunrise and Sunset are defined as when the 
Center of the Sun is on the Horizon, NOT first / last light.

Some propagation "experts" have done the DX community
a serious disservice with inaccurate low band propagation
information based on unproven theoretical predictions and
totally ignore recommendations of EXPERIENCED DX'ers
who have WORKED many exotic DX stations aiming their
antennas along the terminator to the SOUTH at sunrise
and sunset.

I remember one DXpedition to SE Asia whose operators
adamantly refused to activate the Low Bands at / after
East Coast sunrise, saying "don't tell us when to show
up for the East Coast, we KNOW when the bands are
open" (based on their _inaccurate_ propagation program
information that showed the low bands peaking before
sunrise and after sunset).  

Foreign DX spots of this DXpediton on the OH internet 
cluster showed them working their way up from 80 to 40 
to 30 M  BEFORE each of those bands peaked to the 
Eastern USA, filling up with signals from DU, HS, 9M2 etc.
The operators totally ignored the evidence and worked
few if any eastern USA stations, claiming that the bands
just never opened.

VK0IR worked ZERO eastern USA stations on 80M until
day 6 when they finally agreed to listen AFTER their sunrise.
80% of their USA contacts on 80M were made after daylight 
on VK0 as shown in the band breakdown data in their book.

Theoretical models of ANTENNAS have been shown to be
accurate.  IMHO, simplistic propagation prediction programs
leave a LOT to be desired.  Theory must be backed up by
observation and confirmation.

I  LIVE for those short non-direct openings on the low bands !

de  Tom  N4KG   (9BDXCC = 2830+)


On Fri, 15 Sep 2000 Sylvan Katz <jskatz@sk.sympatico.ca> writes:
> 
> Thanks to all who responded to my request for the algorithm for
> producing beam headings. I have the formula that I need.
> 
> The reason I asked for this information is that I maintain and 
> develop code for Gwyn William's, Vice-Chairman of the RSGB 
> Propagation  Studies Committee, to produce the propagation 
> table published each month in
> RadCom. He also uses the software it to prepare propagation tables 
> for DXpeditions
> 
> (eg see http://WWW.DXTECHNOLOGY.COM/ZD9ZM/zd9prop.htm )
> 
> and our own website
> 
> (see http://www.g4fkh.demon.co.uk/ ).
> 
> At the moment  I am in the process of doing a major rewrite of the
> frontend that drives the commercial propagation package. I need to
> compute the beam headings so I can pass the information to the
> propagation softwares.
> 
> Again thanks for the assistance.
> 
> --
> Sylvan Katz
> Saskatoon, Sask
> VE5ZX & G0TZX
> --
> 
> 
> 
> 

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