The American Radio Relay League reminds all amateurs that in case you've missed it, the new RF exposure rules take effect on Monday, May 3rd.
The FCC has announced that rule changes detailed in a lengthy 2019 Report and Order governing RF exposure standards go into effect on May 3, 2021. The new rules do not change existing RF exposure (RFE) limits but do require that stations in all services, including amateur radio, be evaluated against existing limits, unless they are exempted. For stations already in place, that evaluation must be completed by May 3, 2023. After May 3 of this year, any new station, or any existing station modified in a way that's likely to change its RFE profile - such as different antenna or placement or greater power - will need to conduct an evaluation by the date of activation or change.
I did a fairly deep dive into the requirements last May, before I had my Ham Radio Series, so they're not on that separate page, but the first part is "A Little Radio Safety Techno-Geekery", and some examples of how to go about the calculations are in the second part, "A Little More on RF Power Safety and Ham Radio." Besides my writings, the league itself offers things to help you.
"RF Exposure and You" is available in PDF format for free download from ARRL at,
ARRL also has an RF Safety page on its website at,
The ARRL also has a worksheet that helps in the process.
Here's the odd part. There are no instructions that this is to be filed with the FCC or anyone else. I suppose that means you're expected to do the calculations, and keep them on file in case you're questioned at some point. I would presume that would be if a neighbor complains you're interfering with their TV or Stereo or other form of entertainment and an investigation is started. Thankfully, with the switch to HDTV and cable, those complaints seem to be fewer than back with analog TV.
As the ARRL points out, the major change in the rules is that before now, hams were generally exempt from this requirement. That exemption goes away.
There is no preferred format stated for the analysis, but sticking with that ARRL worksheet might be a good thing.
As a quick review, let's look at table 1 in the first of my two posts. This shows the power at the antenna that requires analysis:
The next table in that article tells you the distances (in meters) from an
antenna with one of four gains where the power is expected to exceed the FCC
power density limits. Always use the "Unc." column, for uncontrolled
exposure - note those are always farther away, which means lower power.
The "Con" column, controlled exposure, is for people working in the industry,
expected to be more aware of the need for caution.
If I reduce the 100W power to 85% to account for the transmission line (following the example in the second article) that leaves 85 watts at the antenna. If I reduce that to 30% for the transmitter duty cycle, it's now at 25.5 Watts, far short of the 75 W that requires analysis by the first table. Notice that each frequency band calculates the powers for four different antenna gains. In the very simple cases, say your 12m antenna has 3 dB gain. That means the distance from the antenna where the power exceeds the safety limit is 3.8 meters, or 12-1/2 feet, in the direction the antenna is pointed. If nobody is closer than 3.8 meters from the antenna, you're good.
That's even below the power to the antenna that requires analysis for the 10m band.
I think that between the various resources I've linked to here, both the
ARRL's handouts and my articles, you should have what you need to determine
how to do the analysis for your station. As a general approach, there's nothing wrong with making worst case assumptions. Saying you're delivering the full 100 Watts to the antenna - or a full 100% duty cycle. That way you know you're always delivering less power to anyone near the antenna and that they're always safer than the limits.