Electromagnetic energy may be considered as ionizing and non-ionizing radiation. When radiation is 'ionizing,' it means that it can separate electrons from an atom to create ions. Lower frequency radiation, which includes all amateur radio frequencies, is non-ionizing. Regardless of the power of the signal, the frequecies of VHF and UHF signals are too low to dislodge the electrons. (Gamma and alpha radiation are both ionizing radiation.)

Last edited by jsharris1229. Register to edit

Tags: radio waves uhf vhf safety section5.6

Experimental data indicates the frequencies that are easiest for the human body to absorb are between 30 MHz and 300 MHz. This means that this range requires the lowest exposure or MPE. Since only 50 MHz falls in this range, it is the correct answer. All other frequencies are not within MPE limits.

Tricky question since easy absorption gives 30 - 300 MHz the HIGHEST value, or risk, of reaching a maximum exposure limit.

Additional information and a great chart can be found here.

Maximum Permissible Exposure (MPE) to radiofrequency electromagnetic fields.

Last edited by drfuka. Register to edit

Tags: 6 meter section5.6

Duty Cycle is the ratio of time a circuit is ON compared to the time it is OFF. See the Wikipedia article for a good visualization.

The short answer to this question is that we care how much radiation is absorbed, which is directly relational to how much is emitted. If you emit half as much per transmission time, you can be exposed to twice as many transmissions.

In more depth, the FCC regulates exposure based on Specific Absorbtion Rates, which will depend on factors in addition to the radio's output power, such as the antenna configuration, antenna gain, frequency, physical location relative to the antenna, and geometry of the object absorbing the radiation.

In the Specific Absorbtion Rate formula, the RMS power level of the Electric Field is in the numerator. Because the denominator won't change as long as we're measuring relative to the same object (such as a human), the RMS power level directly relates to the SAR.

How do we connect Duty Cycle to SAR? Well, Duty Cycle can also be written as

D = Average Power / Peak Power

We can then take the Duty Cycle and plug that into a version of the RMS formula for waves:

RMS = Vp√D

Assuming we know the other variables for calculating SAR, we can then calculate the value. Luckily, we don't have to find those values, as the FCC has chosen the standard values for us.

Since most of the values are fixed for amateur radio purposes, there are many online calculators, such as this one from Lake Washington Ham Club that can give you the relevant calculated outputs.

Last edited by zortness. Register to edit

Tags: section5.6

Each of these answers affect a persons exposure to RF energy radiating from an antenna. The frequency of the signal determines how easily the body absorbs the RF energy. As the power level of the signal increases, more energy can be absorbed, increasing the exposure. The distance is important because the power level of the signal drops rapidly with distance. Finally, the radiation pattern indicates the areas where the energy is directed and how it is concentrated.

Last edited by ham_noob. Register to edit

Tags: safety radio waves transmit power frequencies antenna section5.6

As noted in question C02, the body absorbs energy differently at different frequencies. This is because your body has a resonant frequency. (Actually several, depending on the body part.) The other answers listed are not correct. RF field energy does not depend on frequency, lower RF frequencies can penetrate the body and higher frequency RF fields are not transient in nature any more than any other frequency.

Last edited by jsharris1229. Register to edit

Tags: safety radio waves section5.6

All of these are correct. In most cases, either the FCC OET Bulletin 65 (found at http://www.fcc.gov/Bureaus/Engineering_Technology/Documents/bulletins/oet65/oet65b.pdf) or computer modeling are sufficient.

Last edited by bdengle32@yahoo.com. Register to edit

Tags: safety radio waves section5.6

The human body absorbs RF energy and acts like a resistor. A resistor turns electrical energy into heat energy. If the body absorbs too much RF energy, it means that it will create enough heat to damage tissue in the form of a burn, a painful RF burn. Touching an antenna will not cause radiation poisoning because RF is non-ionizing radiation and thus lacks the energy required to cause it.

Last edited by benton. Register to edit

Tags: antenna safety section5.6

RF radiation "radiates" outward from the antenna, therefore, it is the antenna that must be moved. Relocating the transmitter will have no effect, provided the transmitter is connected to the antenna correctly. Increasing the duty cycle would have the reverse effect - it would increase your exposure.

Duty cycle is the ratio of how much time the transceiver spends transmitting to how much it spends receiving; thus, the more you transmit, the higher your duty cycle.

Last edited by cstromc. Register to edit

Tags: safety fcc operating procedures antenna section5.6

Any time you change your equipment, it's a good idea to re-evaluate your station to ensure compliance. You do not inform the FCC because the amateur service is designed to be self-policing. The SWR of your system will only ensure efficient power transfer, not compliance with safety regulations.

Last edited by archigan. Register to edit

Tags: safety radio operation section5.6

Duty cycle affects average exposure level, which is what the Maximum Permissible Exposure (MPE) limits are based on. A person is more likely to tolerate a one- time, high peak exposure of very short duration than a lower exposure over a long period of time. This is where duty cycle is important because it is a measure of the transmit and non-transmit times, which determines the average exposure. Antenna feedline losses and amplifier thermal effects have nothing to do with RF exposure.

Last edited by kabob. Register to edit

Tags: safety radio operation section5.6

The duty cycle is made up of 'on' times and 'off' times. It is defined as the ratio of on-air time to total operating time. A 50% duty cycle means that 50% of the time, the station will be transmitting.

Last edited by kd7bbc. Register to edit

Tags: radio operation section5.6

RF energy cannot break chemical bonds, they don't have the energy required to cause genetic damage.

Source: According to John E. Moulder (Biological Effects of Power-frequency Fields as they Relate to Carcinogenesis, University of Wisconsin, 1995, p. 209:309-324), professor of Radiation Oncology, because non-ionizing electromagnetic (RF) energy cannot break chemical bonds, they don't have the energy required to cause genetic damage.

Last edited by kd7bbc. Register to edit

Tags: none

A good rule of thumb for Amateur Radio -- always -- is that you are responsible for your own emissions. Any time you are transmitting you are responsible for the consequences.

This holds true whether you are talking about RF exposure limits, avoiding interference with other stations or devices, or even having safe harmonics which don't exceed limits on other bands and cause interference there. You should be remembered when you choose a transceiver -- even if you don't know you are causing a problem it is still your responsibility.

Thus you (the station licensee) are responsible for preventing unsafe RF exposure from your station.

Last edited by kd7bbc. Register to edit

Tags: none