Thursday, May 19, 2011
Congressman King said that he fully understands and appreciates the importance
of Amateur Radio and the service it provides to the community, and that he would see to the modification of the bill so that the 420 - 440 MHz band would be
excluded from the spectrum to be auctioned. The delegation included Mike
Lisenco, N2YBB, ARRL Section Manager for New York City / Long Island (NLI),
Peter Portanova, WB2OQQ, NLI Local Government Liaison (LGL), George Tranos,
N2GA, NLI State Government Liaison (SGL), and Jim Mezey, W2KFV, NLI ARES Section Emergency Coordinator (SEC).
"The Congressman went on to explain that it was never his intention to remove
the 70 centimeter band from Amateur use. He further asked us to `get the word
out' and inform the Amateur Radio community that 70 centimeters is not in
jeopardy," said Lisenco.
Lisenco, Mezey and Tranos spoke about the importance of Amateur Radio emergency communications while Portanova, who is also the local AMSAT representative, addressed satellite and other amateur use of the 70 centimeter band.
The Congressman was very receptive to the group, who also extended an invitation to attend Field Day locations in his District.
(Comment: All expressions are presented in Gaussian electromagnetic units.)
When electromagnetic field propagates x direction, both dipoles will will feel the same field at the same time, and the total electric dipole of the system will be p=2gE. Since the dipoles are not close to each other, the system will also have higher moments (e.g. quadrupole), and its radiation will not be pure dipole radiation. However, the order of magnitude estimate of dipole radiation will suffice in an estimate of the cross section. We note the the power radiated by a dipole must be proportional to p2, since the electric field must be proportional to charge (and thus to dipole moment), and the power is proportional to squared field. From dimensional considerations, the radiated power must be of order cp2/L4, where c is the speed of light. Substituting, expression for p, and dividing the result by the flux of the incoming wave, we find that the cross section is of order g2/L4. (This expression could be obtained directly from dimensional analysis.)
When electromagnetic field propagates z direction, both dipoles will feel field pointing in opposite directions, and consequently the total dipole moment will vanish. However, one can easily convince himself, that non-vanishing elements of quadrupole moment are of order Q=pa=gaE. From dimensional considerations, we can also establish that the radiation of quadrupole is of order cQ2/L6. Substituting, expression for Q, and dividing the result by the flux of the incoming wave, we find that the cross section is of order g2a2/L6. Since L=2a, this expression is of the same order as cross section obtained in the i previous ("dipole radiation").
Those results really should not be surprising: Once we established that cross section must be proportional to squared charges (and thus to g2, and keeping in mind that the units of g are [length]3, we must divide g2 by something with dimensions [length]4 to obtain a cross section (that has units [length]2). Since a and L are of the same order, we can use one of them to get the correct result g2/L4.
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HOW TO READ PROPAGATION NUMBERS
The A index [ LOW is GOOD ]
- 1 to 6 is BEST
- 7 to 9 is OK
- 11 or more is BAD
Represents the overall geomagnetic condition of the ionosphere ("Ap" if averaged from the Kp-Index) (an average of the eight 3-hour K-Indices) ('A' referring to amplitude) over a given 24 hour period, ranging (linearly) typically from 1-100 but theoretically up to 400.
A lower A-Index generally suggests better propagation on the 10, 12, 15, 17, & 20 Meter Bands; a low & steady Ap-Index generally suggest good propagation on the 30, 40, 60, 80, & 160 Meter Bands.
SFI index [ HIGH is GOOD ]
- 70 NOT GOOD
- 80 GOOD
- 90 BETTER
- 100+ BEST
The measure of total radio emissions from the sun at 10.7cm (2800 MHz), on a scale of 60 (no sunspots) to 300, generally corresponding to the sunspot level, but being too low in energy to cause ionization, not related to the ionization level of the Ionosphere.
Higher Solar Flux generally suggests better propagation on the 10, 12, 15, 17, & 20 Meter Bands; Solar Flux rarely affects the 30, 40, 60, 80, & 160 Meter Bands.
K index [ LOW is GOOD ]
- 0 or 1 is BEST
- 2 is OK
- 3 or more is BAD
- 5 is VERY VERY BAD
The overall geomagnetic condition of the ionosphere ("Kp" if averaged over the planet) over the past 3 hours, measured by 13 magnetometers between 46 & 63 degrees of latitude, and ranging quasi-logarithmically from 0-9. Designed to detect solar particle radiation by its magnetic effect. A higher K-index generally means worse HF conditions.
A lower K-Index generally suggests better propagation on the 10, 12, 15, 17, & 20 Meter Bands; a low & steady Kp-Index generally suggest good propagation on the 30, 40, 60, 80, & 160 Meter Bands.
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