Absolutly a great find. Explains in a language even I can understand.
Sent from my Sprint Samsung Galaxy® Note 4.
-------- Original message --------
From: Travis Burgess via BVARC <[email protected]>
Date: 10/11/2015 7:33 AM (GMT-06:00)
To: [email protected]
Cc: Travis Burgess <[email protected]>
Subject: [BVARC] Those Confusing Numbers
This was posted today on the GQRP Yahoo group.
TravisK5HTB
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Hello Group ...
The propagation figures can be confusing and so here is a quick explanation:
HF Propagation Terms Explained If you are looking for overly technical
explanations, this might not be the best read for you, I like to keep things
simple. It’s possible that the information presented may not be completely
accurate, it’s only my interpretation of lots of things that I have read, or
heard. I can say that I have used this understanding of HF Propagation,
balanced against real monitoring over a number of years and found that what I
think should be happening looking at the numbers is usually about right. I do
however urge you to delve a bit deeper than this so you might better understand
HF Propagation.
SOLAR FLUX INDEX or SFI
SFI is a figure derived from the number of active sunspots visible on the face
of the sun based on observations of thermal and radio noise received at a
wavelength of 10.7cm. (2.8GHz). Thermal noise is related directly to the amount
of plasma trapped in the magnetic field in active regions of the sun, this is
related to the amount of magnetic flux generated by these active regions. The
higher the SFI the better for dx'ing on the higher HF bands.
SUNSPOTS
A SUNSPOT is an area of intense magnetic activity on the surface of the sun
which is cooler than the rest of the sun’s surface. Sunspots are vital for
long distance radio communications, linked as they are to the ionisation level
of the F layer. The more active sunspot groups, the more sunspots the better
the dx'ing on the higher HF bands.
SMOOTHED SUNSPOT NUMBER or SSN
When we plot the daily sunspot numbers, it's goes up and down all over the
place. so smart people came up with a way to average out the bumps, called
smoothing, which gives us the SMOOTHED SUNSPOT NUMBER or SSN. In the years
where there are few sunspots, propagation on the higher bands can be
nonexistent. It's not all bad news though as things on the low bands tend to
improve with decline in solar activity. Again larger SSN numbers mean better
conditions on the higher HF bands.
SOLAR CYCLE
Every 11 years or so the sun goes through a cycle of events. At the start of
this cycle, some new sunspots begin to show up on the blank solar disc. With
this first few sunspots things start to improve on the higher HF bands. More
and more sunspot groups show up over the years of the cycle, with continuing
improvements in HF activity. 11 years for the cycle is just an average, really
it can be from 9 to over 15 years. Solar activity refers to a combination of
the amount of sunspots, and the solar geomagnetic activity's effect on the
earth's magnetic field. For the higher HF bands more sunspots usually means
improved conditions.
A and K INDEX
When talking about the solar cycle the numbers are based on smoothed numbers,
this means the monthly average rather than the figures for each day. Using
'smoothed' numbers gives more accurate results, daily solar activity varies
dramatically, making accurate results difficult. A and K INDEX are measurements
of the magnetic field activity that are used in predictions.
The K index is a reading of the magnetic activity as compared to a quiet day
made from various locations. This index in the range 0-9. The K index is the
average of of these readings.
K = 0 Inactive
K = 1 Very quiet
K = 2 Quiet
K = 3 Unsettled
K = 4 Active
K = 5 Minor storm
K = 6 Major storm
K = 7 Severe storm
K = 8 Very severe storm
K = 9 Extremely severe storm
The A index relates to geomagnetic stability and is calculated from K indices
for the previous day.
A = 0 - 7 Quiet
A = 8 - 15 Unsettled
A = 16 - 29 Active
A = 30 - 49 Minor storm
A = 50 - 99 Major storm
A = 100 - 400 Severe storm
A quick example of the A & K numbers
If we are waiting for excellent conditions on the HF bands, then we are looking
A and K indices of 0 lasting for a few days. Combined with a high SFI.
If your interests are the lower HF bands, low A and K indices with very low SFI
numbers would be the go.
In the real world generally propagation conditions are OK when the A index is
10 or lower, and the K index is 3 or lower and the SFI above 90.
However there are countless stories about surprises on supposedly dead bands.
Basically:
The A index [ LOW is GOOD ]
· 1 to 6 best
· 7 to 9 is OK
· 11 or more not so good
K index [ LOW is GOOD ]
· 0 or 1 best
· 2 is OK
· 3 or more not so good
· 5 is really terrible
SFI index [ HIGH is GOOD ]
· 70 not good
· 80 good
· 90 better
· 100+ best
Dave, G4AKC http://www.qrz.com/db/g4akc
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