November 2020 Quiz SOLUTION

November 2020 Quiz SOLUTION

RF Electromagnetic Field Exposure Limits

Here are the correct answers for the November Quiz.

  1. In Canada, the limits for human exposure to RF Electromagnetic radiation are defined by:
    A) Health Canada Safety Code 6
    B) FCC-19-126
    C) The transmitter manufacturer’s User’s Guide
    D) Industry Canada RIB-4
    E) ISED Canada RIC-3
  2. According to the document in Question 1, below what frequency is electric field nerve stimulation (NS) the primary effect of electromagnetic fields on the human body, and therefore the basic exposure limit in that frequency range is specified by the Electric Field Strength?
    A) 1 MHz
    B) 10 MHz
    C) 30 MHz
    D) 1 GHz
    E) 3 GHz
  3. At frequencies between that specified in Question 2. and up to 6 GHz, the exposure limits are defined by the Specific Absorption Rate (SAR) and estimated by calculating the Power Density. At these frequencies the primary effect of RF fields on the human body is:
    A) Genetic Mutations
    B) Skin tingling
    C) Headaches
    D) Thermal effects (heating)
    E) Memory Loss
  4. The Power Density in the far-field (e.g. several wavelengths away) of an antenna can be estimated using the formula PD = EiRP/(4 x pi x D^2) where EiRP is the effective radiated power in Watts and D is the distance from the antenna in meters. In the amateur 2m band, the allowable reference level for Power Density in an uncontrolled environment (e.g. your neighbour’s yard) is:
    A) 100 Watts
    B) 1.291 Watts / square meter  ≤– (only answer with the correct units for power density)
    C) 3.142 W/m
    D) 1 kW
    E) Any power density that does not induce headaches 
  5. Your neighbour, who’s yard starts 10m away from your 1/4 wavelength 2m ground-plane  antenna (0 dBi gain), expresses concern about possible adverse health effects in their yard and house from your 100W FM transmissions.  Which of the following responses would be the most appropriate?
    A) “Don’t worry, radio waves are harmless. I’m exposed to them all the time, do I seem normal to you?”
    B) “The Health Canada allowable power density for the 2m band is up to 1.291 W/m^2 (ref: _____). At your fence, 10m away from the antenna, even if I transmit at my radio’s maximum power of 100 W, the actual power density would only be PD = 100W /(4 x pi x (10m)^2) = 0.08W/m^2. So you see, even in the worst case at the closest part of your yard, the power density from my antenna is only 1/16th of the Health Canada allowable limit. This is a very low power density compared to the safe allowable limit so I wouldn’t be worried at all if I were you. But feel free to have someone independently check my math if you’re still concerned – I’d be glad to answer any questions and cooperate fully.”
    C) “The safe power density is up to 10 W/m and your yard is 10m away, so the power density at your fence is 100/10 = 10 W/m. I’m right on the maximum allowable limit, so there’s nothing you can do about it.”
    D) “It’s the 2m band, which means as long as you keep 2m away from the antenna, you’re fine. You’re just lucky I’m not on 20m or 40m!”
    E) “I have a license for it. If you don’t like it, complain to ISED.”

Congratulations to those who submitted correct answers and I hope this served as a fun refresher.

Correct answers received so far:

  1. Wayne VE2WRH
  2. Rick VE7RY
  3. Malcolm VE2DDZ