HFU HF Underground

Technical Topics => Part 15 AM and FM Station Operation => Topic started by: k6sti on June 21, 2021, 1202 UTC

Title: 13.56 MHz Legal Power Revision
Post by: k6sti 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: