[TowerTalk] ALL THE RIGHT ANGLES ?

[T A RUSSELL]

On Tue, 11 Aug 1998 16:30:02 -0400 Pete Smith <n4zr@contesting.com>
writes:
>
>At 04:00 PM 8/11/98 -0400, w8ji.tom wrote:
>...
>>The "real" optimum angle may be quite different than the measured or
>>modeled optimum angle and varies from day to day and moment to moment 
>and
>>can not be measured or modeled with antennas at one height. After 
>many
>>suggestions wave angle can be measured near earth, I'm glad to see 
>others
>>recognize the serious flaw in that thinking. 
>>
>>Models of wave behavior in complex and esoteric things like dirt or
>>ionosphere need validation or they are just guesses.
>
>Just 2 comments:
>
>First, of course the predictions are just that, and have only 
>statistical
>validity.  They probably won't describe the actual situation if you 
>could
>measure it at any given time, which is why they use the monthly 
>average SSN
>as their key parameter.
>
>Second, in the case of IONCAP and VOACAP, the predictions are *very*
>validated, through a network of observers and observations that go 
>back
>through at least 3 complete solar cycles.  The VOACAP suite also 
>includes
>ICEPAC, which also produces the probability that a given path will be 
>open,
>at a given frequency and time of day, for a given solar flux.  That's 
>a
>pretty useful number for band planning in contests.
>   
>
>73,  Pete Smith N4ZR
>In wild, wonderful, fairly rare WEST Virginia
..................................................................................

N4KG  comments on Propagation Prediction programs:

I have two reservations about most propagation modeling programs.

First, since they are based on AVERAGE solar data, they
UNDER-ESTIMATE  the PEAK  MUF.  The better programs 
are reasonably accurate about the TIME at which the peak 
occurs, but I have often seen 12M and even 10M open 
when the IONCAP monthly predictions shows the MUF 
barely  above 22 MHz.

Second, MOST simplistic propagation programs do NOT
accurately indicate the PRE - SUNSET  and  POST  SUNRISE
peaks on the low bands.   Even CAPMAN, which is a reasonably
accurate HF propagation prediction program, totally misses the
very reliable 40M  LP opening to VK6 and barely shows it as 
a brief possibility on 30M.  In actuallity, VK6 can even be worked
on 80M BEFORE  sunset  in W4 and is a solid 1 hour opening
on 40M.   Forget about trying to predict marginal polar paths
on the low bands with the simplistic programs.

de  Tom  N4KG


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