Saturday, December 4, 2010
Amateur Radio Antennas and Radiation
The very first question I was asked about was, “Will the antennas cause cancer and our hair to fall out?”
If there is a word guaranteed to cause apprehension, it is “radiation”. Amateur Radio uses the word in a much broader sense--radiation pattern, feed line radiation, antennas radiate--and that can be confusing to the layman. It is true that radio frequency energy is a form of radiation, but it is far different from the radiation used for cancer treatment or emitted by radio active materials.
Radiation from antennas is not the same as ionizing radiation from radioactivity. Radio frequencies are not nearly high enough for a photon of radio energy to cause an electron to leave the atom (ionize) as discussed when talking about ionospheric propagation. That is the difference between ionizing and non-ionizing radiation of which radios waves are the latter type.
Before radio ways can be considered ionizing, their frequency would have to be increased far beyond microwaves, through visible light and on the upper reaches of the ultraviolet and x-ray spectrum. The radiation from radioactivity is carried by atomic particles such as the nucleus of a helium atom (alpha radiation), an electron (beta radiation), neutrons, or gamma-ray photons with frequencies even higher than ex-rays. These are billions of time more energetic than the radio waves cause by Amateur Radio Operators.
Biologic (athermal) effects such as genetic damage have never been observed at amateur frequencies and power levels. That requires the energy of ionizing radiation. The only demonstrating hazard from exposure to RF energy is heating (thermal effects) and that occurs only in very strong fields. RF “burns” are caused by touching conducting surfaces that have a high RF voltage present and are a very localized instance of heating that carries no more risk than thermal burns from hot objects.
So, if you are ever approached by a neighbor or some local authority this would be your best explanation to give.
Not only is it true but they will walk away scratching their heads.
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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