Reliance upon repeaters or repeater systems for emergency communications is not wise. It is not uncommon for a repeater to fail, or be knocked out by some external force (e.g.- lightning, high winds, etc.). Repeaters can also be very "political."
Since the beginning of radio, the focus by most amateurs has been to see how far they can reach out with their signals. While DXing is an enjoyable pastime, it is rarely needed for EMCOMM, DON'T RULE IT OUT COMPLETELY FOR PUBLIC SERVICE! The ability to effectively pass traffic over long distances is often important, even lifesaving!
HF signals propagate either by a) line-of-sight; b) ground-wave (follows the contours of the earth); or c) sky-wave. Line-of-sight is usually good for a few miles.
Ground-wave is usually good from about 20 to 50 miles. NVIS sky-wave takes over at about 50 miles, and depending upon the frequency selected is good out to 500 miles. Beyond that, we are in the general area of low-angle DX.
NEAR AND FAR
Very often, a 40 meter signal at mid-day, can be heard near and far, all three types of propagation at the same time! To explain propagation, whether low-angle DX or NVIS, or somewhere in-between, I often use this illustration: Just as a billiard ball can be bounced toward a particular pocket by controlling the angle that it hits the bumper of the pool table, so do radio signals "bounce" (actually refract is more descriptive) off the ionosphere. Now, envision the earth as a round pool table with the ionosphere as the circumference or boundary. This "bumper" is constantly expanding and/or contracting in concentric circles, and varies in density often depending upon the time of day, the season, recent solar activity and/or the sun-spot cycle. This phenomenon is a science unto itself and is not the subject here. Just know that for local and regional EMCOMM, NVIS HF (usually in the 40 and 75/80 meter bands) can provide reliable communications over mountain ranges and under the most extreme conditions. The big advantage is that we are not dependent upon some remote mechanical device.
NVIS MADE SIMPLE
I (and others) have experimented with simple (1/2 wave doublet, G5RV, etc.) wire HF NVIS antennas as low as actually lying on the ground to 3 feet above ground, and they work amazingly well! A lot depends upon ground (earth) conductivity and how far down below the surface the moisture content may be. However, I recommend that any antenna be at least 8 ft. above the ground to prevent someone from tripping over it.
Remember that the higher you elevate a flat (horizontal) antenna (e.g. a simple wire doublet or G5RV) above earth ground, the more the NVIS effect will be lessened. A little height will allow for better line-of-sight and ground-wave propagation. I find that 25-30 ft above the earth works fairly well both near and far. Also the higher you go, the more directional it will be. An Inverted V antenna, at any height, will be less directional, but the NVIS effect will be less than a "flat-top."
OTHER "REPEATER FREE" OPTIONS
Also, to avoid reliance upon repeater(s), don't rule out VHF simplex. Don't believe the myth that VHF is strictly "line-of-sight!" I routinely communicate PTP (Point-To-Point) over 50 miles on 2 meter FM simplex using only a simple ground plane antenna 20 ft. up...and with a mountain range between my station and the other! And over 100 miles routinely using a 13 element Yagi. I also communicate 300 miles on 2 meter SSB and/or CW using a 13 element Yagi (horizontal polarized). A skilled relay operator in the right location doubles these ranges! Also, consider six meters simplex FM, SSB, CW for EMCOMM.
There are so many variables, regular participation in nets will provide you with the experience and knowledge of what works and what doesn't!
As far as of lack of interest in serious EMCOMM by hams is concerned...I wish I had the answer! All you can do is to try to explain that skilled and disciplined operators become that way and also maintain their skills by regularly participating in regularly-scheduled properly-run (non-repeater) public service nets. If there isn't one in your area...why not start one?
Drawn from: http://www.emcomm.org/archives/EQ/2010/summer2010.htm
Monday, December 13, 2010
Posted by R. Small at 10:23 AM