Graphic courtesy of Matt, N9NPP
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Purpose of this Page
During conversations and e-mail exchanges with SKYWARN volunteers from various parts of the country, it seems that new technologies with SKYWARN applications are being taken advantage of only sporadically, often in relative isolation. Limited interface from locale to locale reduces the "cross pollination" that might aid in the spread of useful techniques.
The manufacturing technology explosion occurring in Japan has brought many new technologies within economic reach of many SKYWARN spotters. We could do a better job of taking advantage of the opportunities provided by this technology!
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Amateur Television (ATV)
ATV - Amateur Television - This includes both Slow Scan (SSTV) and Fast Scan Television (FSTV).
SSTV uses the narrow bandwidths associated with voice communications and as a result, is limited to a relatively slow image transfer rate. However, SSTV could be effectively used for relaying storm images to the net or for damage assessment (using a secondary frequency). Kenwood has become the leader in affordable slow scan TV equipment usable for mobile applications with the introduction of the VC-H1. Using this device, single video frames can be sent over virtually any circuit suitable for voice communications. The VC-H1 will also save your images as a jpeg file, which could then be sent over the internet or via packet radio.
If you have a PC with a sound card and a shortwave receiver, you can sample HF (shortwave) SSTV by using one of the software programs available on the following pages:
Tune to 28.680 MHz +/- a few kHz for SSTV
FSTV requires considerably more bandwidth, but delivers high quality full motion images similar to commercial television. It is fairly common to hear about weather radar transmitted via FSTV. What is uncommon though, is to hear about over the air spotter training being transmitted via FSTV. It is also uncommon to hear of SKYWARN organizations that train either their net control operators or SKYWARN spotters how to interpret weather RADAR. See: Central Oklahoma RADAR signatures
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Automatic Position Reporting System (APRS) - If there was ever a technology that was a match for emergency communications, it's APRS. Coupled with a RADAR display and mapping software, APRS could allow a net control station to know exactly where spotters are located relative to a storm and effectively direct questions to the spotter most likely to be able to make the needed observation. I am suggesting that all of this information should be displayed on one monitor simultaneously. Has any SKYWARN group already created this capability? Are there any software gurus willing to develop this capability?
In addition, APRS can provide the exact location of storm damage for directing emergency crews during search and rescue operations and later for damage assessment reports. Again, Kenwood is the leader in this technology for amateur radio.
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Amateur Satellites - I have long watched the development of amateur satellite technology with thoughts that some day they might be usable for emergency communications. The new amateur satellites that have been placed in highly elliptical orbits now offer that possibility. Take a look at AMSAT, the Radio Amateur Satellite Corporation's homepage.
Hams have traditionally provided emergency communications after disasters. In many cases, HF communications using the ionospheric propagation was used, especially when the disaster occurred in rural or relatively isolated locations. However, HF communications can be unreliable, depending on Solar-terrestrial conditions, interference and other factors. Long boom yagis can extend the range of 2 meter FM voice, packet or SSB to 100 miles or greater, depending on terrain, transmitter power, antenna height and other factors, but may not always cover the distance needed. Some areas are crisscrossed by repeater networks that can be linked to provide distant connections, but many use commercial electricity with no emergency backup, that may not be available after a disaster.
That brings us to Satellite communications (SATCOM). SATCOM could provide more reliable communications than either HF ionospheric or VHF tropospheric propagation. Even though FEMA and the U.S. military have SATCOM capability, there may be occasions when their resources are either not available or slow to deploy. Amateur SATCOM could fill in the gap.
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HF Communications and Near Vertical Incidence Skywave (NVIS) Communications
Back in the 1960s during a vacation to Yellowstone National Park with my parents, I saw several amateur antenna arrays that caught my attention. We passed by the homes of amateur radio operators in Wyoming who had erected strange antenna systems. These antennas consisted of four telephone poles arranged in a square with wire strung between the poles. The array wasn't large enough to be a rhombic antenna. At the time, I was around 12 years old and was only starting to learn about radio. As a result, I was uncertain what these might be used for.
Several years later after getting my amateur radio license, I decided to copy the idea. Having been exposed to cubical quad antennas as an inexpensive way to build a directional array for HF, I decided that perhaps the horizontal loops that I'd seen several years earlier may have been one wavelength quad loops, with the plane of the loop horizontal or parallel to the ground (i.e., a "lazy quad"). Having studied the ARRL Antenna Handbook, it became obvious that the arrays I'd seen in Wyoming were pointed straight up! So, I put one up for 80 meters. It was only 1/8th wave above the ground, but it worked very well out to about 400 miles or so. Beyond that, my inverted vee dipole and 14AVQ loaded vertical started working better.
The loop was quiet and stations around Texas, Oklahoma and Louisiana were loud! It was a super antenna for "short skip" and worked well for 75 meter Hurricane and traffic nets.
Here is URL to a book devoted to Near Vertical Incidence Communications:
And several more links with valuable information posted:
Yahoo NVIS Search Results
These links should help you get started.
From my perspective, assuming you intend to use the ground as your reflector, the optimum height for your antenna is 1/4 wave. This applies to dipoles and loops. As the height is reduced below 1/4 wave, ground losses increase rapidly. At 1/4 wave, the antenna will exhibit a nice big lobe with the maximum pointed at the zenith (straight up).
A reflector or reflectors may be added to increase efficiency. Antennas erected above poorly conductive soil, such as sand, will benefit the most from the addition of reflectors.
A horizontal "flat top" (not an inverted Vee configuration) dipole is probably the easiest to erect, since it requires at a minimum, two supports, and perhaps three for optimum mechanical strength. However, a one wavelength loop (a "lazy quad"), provides slightly more gain (approximately 1.4 dBd) and immunity from precipitation static.
Inverted Vee dipole configurations will not work as well because they will exhibit a lower angle of radiation.
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Voice Over IP
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Last revised: December 25, 2003