On Sat, 16 Dec 2006 01:22:44 +0000, Jim - NN7K wrote:

Owen is correct- and anyone operateing 10& 6
meters will tell you the same thing!

Good morning, Jim.

What I'm trying to figure out is the effect of sporadic E on the lower
bands, e.g. 75 meters.

I was on a military net on a frequency somewhat above 4 MHz and was able
to work a station 70 miles away, well after dark when the critical
frequency was below 3 MHz. According to everything I know about critical
frequencies and MUF (which isn't very much), my NVIS signal from my
17-foot-high dipole should have gone right off into space, and the
70-mile-away station shouldn't have heard a peep out of me (and vice versa).

I'm trying to figure out if the solar storms of the last few days might
have something to do with why I was able to contact that station when
every indication was I shouldn't have been able to. Sporadic E? I dunno,
maybe, but it seems like quite a stretch...

People are staring to take the computer predictions, simulations and
forecasting too seriously. Atmosphere and ionosphere are very complicated
and are run by Sun and not some wiz programs.
Before the computer models, we used to OBSERVE and LEARN about propagation
from our activities on the bands. Changes with sunspot cycles, time of year,
day etc.
So forget the computer prescriptions and observe and make notes what is
happening when Sub is doing what. One general observation I have found that
with low sunspots in a cycle atmosphere shrinks, angles get lower and
antennas with low angle lobes work better. At High sunspot, atmosphere gets
higher and angles get higher and higher frequencies come to live.
The best, unpredictable and unbehaved band is 160 m, you never know what
happens, just need to be around when IT happens.
Check out http://members.aol.com/ve3bmv/bmvpropagation.htm
on my observations and notes on ducting and refraction.

73 Yuri, K3BU
"C. J. Clegg" wrote in message
news
On Sat, 16 Dec 2006 01:22:44 +0000, Jim - NN7K wrote:

Owen is correct- and anyone operateing 10& 6
meters will tell you the same thing!

Good morning, Jim.

What I'm trying to figure out is the effect of sporadic E on the lower
bands, e.g. 75 meters.

I was on a military net on a frequency somewhat above 4 MHz and was able
to work a station 70 miles away, well after dark when the critical
frequency was below 3 MHz. According to everything I know about critical
frequencies and MUF (which isn't very much), my NVIS signal from my
17-foot-high dipole should have gone right off into space, and the
70-mile-away station shouldn't have heard a peep out of me (and vice
versa).

I'm trying to figure out if the solar storms of the last few days might
have something to do with why I was able to contact that station when
every indication was I shouldn't have been able to. Sporadic E? I dunno,
maybe, but it seems like quite a stretch...

That supposed to be ...starting.... and Sun.... not Sub :-)

Even spellchecker can fail :-)

73 Yuri

Yuri Blanarovich wrote:
Even spellchecker can fail :-)

My spellchecker says that "spellchecker" is
misspelled. :-)
--
73, Cecil http://www.w5dxp.com

C.J. as to the E layer, its effect is probably
next to nil that low in frequency, but, if memory
serves, think that there is a "D" layer, below the
"E" layer, that might have the properties you
speak of? I might have missed some, as I only
download 35 messages at a time, because of all the
junk debates (code-no code, ect). But you raise a
interesting subject as I use on 80, a G5RV, pushed
to its limits (about 15-10 feet off the ground)!
Yet I hear stations that people with higher
antennas cant hear, and it is heard better than
folks with much better antennas than this!
Frankly, this should compare to a wet noodle,
yet consistantly seems to work out to several
hundred miles at night,and on 40 during the day.
The reason it like this is NO TREES in Nevada,
and this property is on bedrock! Not saying this
is an effecient setup , just that it seems to
work! Oh well, sorry for the trouble- thought you
talking about VHF! Jim NN7K



C. J. Clegg wrote:
On Sat, 16 Dec 2006 01:22:44 +0000, Jim - NN7K wrote:

Owen is correct- and anyone operateing 10& 6
meters will tell you the same thing!

Good morning, Jim.

What I'm trying to figure out is the effect of sporadic E on the lower
bands, e.g. 75 meters.

I was on a military net on a frequency somewhat above 4 MHz and was able
to work a station 70 miles away, well after dark when the critical
frequency was below 3 MHz. According to everything I know about critical
frequencies and MUF (which isn't very much), my NVIS signal from my
17-foot-high dipole should have gone right off into space, and the
70-mile-away station shouldn't have heard a peep out of me (and vice versa).

I'm trying to figure out if the solar storms of the last few days might
have something to do with why I was able to contact that station when
every indication was I shouldn't have been able to. Sporadic E? I dunno,
maybe, but it seems like quite a stretch...

Jim - NN7K wrote in
. net:

....
work! Oh well, sorry for the trouble- thought you
talking about VHF! Jim NN7K
....

There seems a theme in some of the postings that Sporadic E is a VHF
phenomena.

Go look at the ionograms from an ionosonde, it can measure the critical
frequency (don't know what that means? consult a text book) of the layers
above itself at the time, and it discovers E and Es layers. The highest
return frequencies indicate the critical frequency, and it isn't
(usually) at VHF, it doesn't need to be to facilitate VHF paths.

If the f0Es is say 10MHz, consider the length of the paths, the virtual
height of the layer and the MUF for the path (approximated by the secant
of angle of incidence * f0Es). If you approximate the earth as flat, a
500km distance to a virtual reflection point at 100km height with f0Es=
10MHz yeilds an angle of incidence of 78deg, sec(78)=5.1, so MUF=51MHz.
The earth is not flat, so a slightly longer path is needed for MUF
50MHz... but the paths commonly worked are 1000 - 3000km, and more. You
don't have to do the calcs, some of the space weather sites will fake up
an oblique ionogram for you, certainly ours can.

Sporadic E is not the only mechanism in long distance VHF contacts, and
contacts are not necessarily dependent on a single mechanism.

But back to the original question, if there is a sporadic E layer
overhead at night, why would it not support NVIS 4MHz contacts?

The maps of f0F2 look pretty, but there is reduction of a lot of
measurements to a single statistic, interpolation and a delay between
measurements and publication that questions their use to prove that the
contacts you had could not happen.

I still ask the question "how can they measure f0F2 when there is such
strong "reflection" from a sustained E layer that no signal returns from
the F layer?".

Owen