|Member News & Views|
Member News and Views is that portion of the ECARS Website set aside for members to present amateur radio related topics of a technical, operational, or administrative nature.
If you have anything to share for the good of ECARS members please send your comments or concerns to Troy, WB2FNG. Articles posted on this page, do not necessarily reflect the views or opinions of ECARS.
a. For those Hams that are looking for other HF Nets to check into when ECARS is not on the the air, "Click Here" (posted 01-18-2016)
b. For those Hams looking for hard to find radio parts, or who need out dated equipment repaired, here's a website to check that may help solve your problem. " Click Here "
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ECARS depends mainly on NVIS propagation in the daytime for communications within the ECARS normal service area.
NVIS propagation normally depends on the D layer to reflect signals back to earth from high angles and cover the area our NCS need to hear and to reply.
For some time now the SUN has been emitting X-RAY radiation from a large coronal area on the Sun's surface.
The X-RAYS travel at somewhat slower speed than light. Depending on the angle of emissions from the Sun, it can take different time intervals to reach the Earth's outer F layers and create a total ABSORPTION in the D layer area. That means no reflections back to earth at high angles. When this happens your signals get absorbed buy the layer that results.
However at low angles there is reflections back to more distant points much of the time out of ECARS coverage areas. This is evident by listening to Mid Cars and South Cars out of area. When this happens we hear the mid western and states farther away and to the south and even Canada.
Variations of the propagation conditions show up when an NCS on the edge of the coverage area can hear stations on the opposite edge of the coverage area without hearing closer in the middle areas.
Very good NVIS conditions show when two stations less than 50 miles apart can hear each other.
As well, as the day progress and we revolve (move) under the sun, the conditions change. This is what we usually call the Band getting longer. As just noted, the band does not really get longer; its that we are moving under the sun. The layers over head change from morning to afternoon to nighttime conditions that change when some layers disappear and cause propagation changes.
For best NVIS communications at high daytime angles, a horizontal antenna some what less than one quarter wave length in height or less then 33 feet is most often more useful. This is due to its pattern being mostly upwards and angles up to 45 degrees off the vertical.
A low dipole is very nearly an Omni directional antenna and does not show very much directivity favoring any direction. A Vertical antenna very often is not the best or preferred antenna because its pattern is mainly low angle and not the best for NVIS high angle use. Of course there are exceptions at times. Its not all attributed to the eleven year sun spot cycle. We are at the mercy of the Sun in any event so hang in there for hopefully better times.
A good indication that tracks most of the time is the WWV Solar Indices near the bottom of page 2 of the ECARS Website.
Take a look and read the info under the Graphs.
I hope this offers some insight on why we have a problem with running the net over the last couple years.
Good luck to everyone.
16 May 2017
I strongly disagree with the statements made about the D-Layer and propagation on the 40 meter band.
I believe the D-Layer basically does very little to reflect signals below 10 MHz.
I believe the main feature of the D-Layer is that it diminishes signals due to absorption.
During the summer months and periods of strong solar activity the D-Layer is at its strongest.
This strong solar activity causes brown / black outs due to a super-charged D-Layer (High absorption).
During the winter months (Tilt of the Earth's axis) the D-Layer is less active (Lower absorption).
(The two equinoxes come into play and define the Earth's ~21 degree tilt.)
A 40 meter signal needs to be reflected back to earth from the E, F1 or F2 Layers. (Excluding Ground Wave.) Passing through the D-Layer and returning to Earth, sometimes becomes impossible below 10 MHz. This is due to the wave being absorbed during the upward path, and even further reduced coming back down. The D-Layer appears in sunlight and dies at sunset, which explains night time DX on the lower frequencies.
It's as simple as that!
NVIS (< 1/4 Wavelength high) antennas only add a small amount of an advantage due to their high take-off angles. Much of the advantage of the low height / high angle of radiation is lost due to "Ground Loss". (Worms like it.) Higher mounted horizontal antennas will still have an NVIS component and have the ability to launch straight up. Higher mounted horizontal antennas (above 1/4 wavelength) will work almost as well when the D-Layer is weakly charged.
NVIS antennas are liked by the military because it keeps the troop from being shot while erecting a tall antenna. It keeps the troops from being spotted by the enemy from a distance. It slightly keeps down longer distant QRM operating on or near a close channel. (Or being heard by the distant Enemy.) It is liked by lazy people that don't want to, or can't , erect a good antenna. (HOA / CC&R's)
I would not be silly enough to physically compare the two, but to ponder a guess I bet an S-7 signal on a tall antenna... would be an S - 7 1/4 on an NVIS system! (If the band was average to good.) We live in a divided world, but take a look at how well stations like K2CGH work short distances with antennas at 80+ feet!
73 / Len / N8AD
PS: Best of 73's is redundant!
15 June 2017