We seek to understand and document all radio transmissions, legal and otherwise, as part of the radio listening hobby. We do not encourage any radio operations contrary to regulations. Always consult with the appropriate authorities if you have questions concerning what is permissable in your locale.

Author Topic: 13.56 MHz Legal Power Revision  (Read 177 times)

k6sti

  • Guest
13.56 MHz Legal Power Revision
« on: June 21, 2021, 1202 UTC »
For years 13.56 MHz experimenters have relied on free-space calculations to estimate legal transmitter power for FCC Part 15 operation in the 13.56 MHz band. Recently I used NEC-2 to calculate legal power for several types of antennas over three types of ground. The power varies with antenna height and ground quality, but in general I found that about half of the free-space value was legal when ground is taken into account.

I've read the FCC rules more closely, including sections that apply but are never quoted by experimenters, and an ANSI document the FCC includes by reference. It seems I've been too conservative in my interpretation of the 30 meter measurement distance that determines maximum field strength. Much higher transmitter power appears to be legal for horizontal antennas than I previously calculated.

The issue is complex. I've started a thread on the LWCA forum to explain everything and promote discussion. It is here:

https://www.lwca.net/mb/msg/11501.htm

Brian