Tuesday, December 16, 2014

Finished My RF Safety Report

Had a really nice one about 90% finished that I'd been working on for three days.

Then I was editing a section of it this morning (no coffee!), and I NUKED the whole damn document..............RATS!

Just finished a frantic 6 hour push to get at least something presentable printed out.

The question of RF Safety on the Iowa is something that's a bit overblown, as getting to the Disc/Cage antenna on the bow means going through a locked gate that only authorized people have the key for. The public can't get within 50 feet of it.

The Trussed Monopole antenna at the stern is located on top of the Helo Ops shack, and is a good 10' above the deck.

Assuming ZERO feedline loss (we don't have a clue what the line loss is, but I'll bet it's at least 2~3dB), the fact that we run *maybe* 100 Watts out of the transmitter, and the fact that the Duty Factor for SSB is 20%, and CW is 40%, the minimum safe distance for the "Uncontrolled Area" (where the public is allowed) is FIVE feet.

There's just no way we're pumping out enough RF to do anything to anybody.


  1. Maybe you've already done this, but a table showing the minimum safe distances and the distances provided can go a long way with your audience that doesn't understand what you're talking about.

    When I'm doing reports like that, I put the table up front as a summary then put the specific calculations behind that. I'm not sure anyone but a few people read behind the table.

  2. (Forgot to check the "notify" button)

  3. Yep, do a graphic and I'd look at painting a 'safety' line on the deck if they'll let you.

  4. The top people are the ones we have to CYA for. One of them is a Ham, and understands the issue exactly, so no problem there.

    Turns out that the minimum "safe" distance is 5 feet, and that's assuming NO coax loss between the transmitter and the antenna. Considering we're going through well over 100' of coax, the loss there is significant, resulting in less power at the antenna, so we have an even greater margin of safety.

    The stern antenna is mounted on top of the Helo Ops shack, about 10~12 feet above the deck, and the bow antenna is even higher than that off the deck.

    We already knew it was a non-issue, BUT we had to go through the numbers, and give the top people a written report so they could convey the results to the regular crew, most of whom know nothing about this stuff.

    And after our meeting today, everybody was happy, so all-in-all it went quite well.


Keep it civil, please....