New FCC RF Safety rules come into effect on May 3 - what you need to know

Discussion in 'Amateur Radio News' started by N2RJ, Apr 27, 2021.

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  1. DO1FER

    DO1FER Ham Member QRZ Page

    Thanks for that video about the new safety rules in the USA. The FCC rules are not the same to the german rules of the BNetzA. And we dont have the difference of the controlled and uncontrolled area. Our calculations are just for the controlled area. If its get over, it is not allowed anymore to transmit anything. At next here in Germany the time of transmitting in the caluclation is more variable. But normaly the 3 minutes are an average time for a calculation within all modes of transmitting.
  2. DO1FER

    DO1FER Ham Member QRZ Page

    That there is no evidence that the human body gets suffered by a electric field, I cant agree with it. In the following link there is a table, what happen by the different levels of a electric field in mA/per squaremeter to a human body. The table is done by a german department for radiation protection and an electricity provider.
  3. W1YW

    W1YW Ham Member QRZ Page

    You bring up an important point on duty cycle. It is key to estimating an accurate 'average' power.

    Averaging has to be defined explicitly for the calculation being sought. Both voice and CW transmissions are only a partial duty cycle . PEP vs so-called average on SSB does NOT include pauses, which thereby shorten the duty cycle. On CW, the duty cycle is closer to 35% or less over the transmission. AM is a high duty cycle, as is FM.
  4. DO1FER

    DO1FER Ham Member QRZ Page

    It seems to be, that this or that is really different. Our calculations here in Germany could be done by hand or with a computerprogram called "Wattw├Ąchter". When you do it manually, you just have to use the basic formula with the average basic terms for the position of E. The average values are

    <= 10Mhz / E=87
    >= 10 Mhz up to 400 Mhz / E=27,5
    >= 400 Mhz up to 2000 Mhz / E=1,375
    >= 2000 Mhz / E=61

    At next you see from the screenshot of the Wattw├Ąchter how to differ the avaible modes and time.

    Formel_Sicher.png screenshot 1
    Wattwaechter.png screenshot2
    K8PG likes this.
  5. G8FXC

    G8FXC XML Subscriber QRZ Page

    "We" as in "Britain" have to follow similar rules now too! I certainly take your point about the uncertainty of coax losses, but the purpose of the simple on-line calculators is to give us an initial estimate of how much more trouble we have to go to... For those of us running 100W into a fairly low-gain antenna, the minimum separation distances are typically a small number of feet - in many cases, there is no need to carry out more detailed measurements because there is so much safety margin. You plug your numbers into the spreadsheet and it tells you that the minimum safe distance is X. If your antenna is 2*X away from your nearest neighbour, then you can realistically claim that you've done everything that is necessary. If it's 1.2*X away from the neighbours, then you probably should take some more detailed measurements...

    Martin (G8FXC)
  6. W1YW

    W1YW Ham Member QRZ Page

    Hi Martin,

    The calculators are not mere 'estimates', but used as tools to 'ensure compliance'.

    K7JEM has a nice inversion of the calculator that conservatively estimates max POWER for a given installation, which assumes, or can assume, lossless coax. So (you know this, others might not) the power can be HIGHER when the actual coaxial insertion loss is measured.

    I am certain that some US hams will not be willing to trade off SINR because of a SWAG estimate, whereas the-- actual-- insertion loss numbers can tell the true power limit.

    Chip W1YW
  7. N2UHC

    N2UHC Ham Member QRZ Page

    I don't know that electromagnetic fields don't harm the human body, but I'm betting that at the power levels we transmit they don't.
    K0VWA likes this.
  8. N1FM

    N1FM Premium Subscriber QRZ Page

    Chip, can you help me with the math on this?

    For example, if I operate a 1500 watt PEP SSB (phone) station that is on for 10 minutes, off for 10 minutes and on again for 10 minutes, I'm operating with 200 watts average power (1500 watts PEP * 20% * 67% = 200 watts average power) over a 30 minute period. In most cases for the 6 minute controlled environment exposure estimate, I should probably assume that it is possible to operate over the entire 6 minute period, so the 1500 watt PEP SSB phone station would be 300 watts average power for controlled-exposure calculations.

    So the duty factor for an SSB signal with no processing is 20%, averaged over a very long-winded 6 minute period = 300 watts. I use resonant dipoles, so that's 2.2 dBi. The distance to the center of my dipole is 9 meters (about 29.5 feet) if standing directly under it (worst scenario in case somebody wanders into the backyard). So, with those numbers, I'm in compliance for every band I operate, with 10 meters being the worst, where distance to compliance is only 7.34 meters or 23.34 feet. I'm using the formulae given in FCC OET Bulletin No. 65 to estimate power density in the main lobe of an antenna, with use of the EPA-recommended ground reflection factor as an option.

    My question: I use 100' of Belden 9913 (RG-8), which exhibits some loss at 10 ten meters. Using this calculator ( ) my loss (worst case) is 0.728 dB at 10 meters. How would I use coax loss to determine a change in my safe distance factor? If I'm losing 0.728 dB in the coax at ten meters, which would reduce my power output into the antenna, wouldn't that make my distance to compliance even less?

    In this calculator ( should I use a lesser number for the dipole calculation, subtracting the coax loss from the 2.2 dBi figure used for dipoles, or would I reduce the average power, based on my coax loss?

    Thanks, de Tom
  9. W1YW

    W1YW Ham Member QRZ Page

    Duty cycle refers to the percent of time 'appreciable' power (nope, not going to entertain any discussions resembling how many angels fit on the head of a pin vis a vis appreciable) is on during the transmission. You cannot include reception. So if you call CQ on CW you have to figure out the average power during the complete transmission, not the complete operating session. You would be within acceptable practice to itself average that over several transmissions. Easy arithmetic. We can handle it.

    You cannot measure coaxial loss to precision of 1/1000th of a dB at HF. If you note that you measure the coaxial insertion loss with an accuracy of, say, 0.1 dB you are compatible with 'ensurance': Look at your thermal and systemic noise in the measurement.

    The average power to the antenna is the desired observable.

    It is simple arithmetic to take the cable assembly insertion loss as dB and then subtract that equivalent in watts relative to the average TX power. That will tell you your average power to the antenna.

    The conversions from and to dB are part of the Tech question set and others--that is, every US ham was asked to master that simple knowledge in order to procure a Part 97 license. MO--not too sympathetic to anyone (else) (US ham) who thinks this simple math is 'yucky':)

    Chip W1YW
  10. W1YW

    W1YW Ham Member QRZ Page


    Decibel-percent converter | Lasercalculator

    0.7 dB coaxial assembly insertion loss means you can increase your TX power by about 15% for a given value of average power to the antenna, compared to the same calculation for that power with no coaxial loss..

    So if you have 1200 watts average TX power as the power limit that takes you outside of the 'safety zone' calculation, done with no insertion loss of that coax, you can actually use about 1375 watts average TX power and be within the safety limit. As an example.

    GIVEN THE AVERAGE POWER ESTIMATE--at the antenna- very few US hams at home locations will encounter a problem on SSB or CW at HF.

    MOBILE HF at medium to high TX power is a very big issue and great care should be exercised to both calculate and execute reasonable distance limits.


    Chip W1YW
    Last edited: May 3, 2021

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