LigoPTP: LigoPTP-3 FCC EIRP rules

Introduction
New rules

LigoPTP 3 products have been certified under FCC Part 90Z rules. This is a licensed band, which is why the rules differ from Part-15 regarding 900MHz, 2.4GHz, and 5GHz unlicensed radios. First, the power (EIRP) limitations are a little different from part-15. Second, any operators of LigoPTP 3 products must obtain a nationwide 3.65GHz license before operating any equipment. Finally, each individual site must be licensed in the FCC ULS database. For more information on the 3.65GHz licensing process, visit this link.

The main purpose of this article is to outline EIRP restrictions, which LigoPTP 3 products must abide by in order to remain compliant with FCC rules.

Software features

The LigoPTP 3 configuration screen provided below shows a the Antenna Gain (dBi) field. When configuring the LigoPTP 3 radio, the gain of the installed antenna must be entered into this field. Once the gain is entered, the software starts to automatically handle all of the EIRP calculations.

365eirp-radio

Rules

Maximum values

LigoPTP 3 EIRP rules are based on frequency and channel size. Each combination of the two may have a specific maximum transmit power and EIRP limit that must be complied with. The following is a chart showing the maximum limits based on frequency and channel size.

fcc1

The power levels provided in the chart show peak output transmit power. The average/conducted output powers may vary and depend on modulation schemes.
Following the rules

There are three main rules to keep in mind when changing Tx power and antenna gain.

  1. The maximum transmit power cannot exceed the value indicated in the Max Tx Power column provided above, given the frequency and channel size.
  2. The EIRP (radio Tx power + antenna gain (dBi) cannot exceed the value indicated in the Max EIRP column provided above, given the frequency and channel size.
  3. There is no limit to antenna gain, as long as the EIRP index does not exceed the value the Max EIRP listed above.

The software handles these rules automatically and does not allow the setting of Tx power and/or EIRP higher than what is allowed.

There are two important configuration options used to control these settings: Transmit Power (%), and Antenna Gain (dBi)

365eirp-power

If it is a LigoPTP 3-18 device, the gain of the antenna is 18dBi, so the value 18 must be entered into this field.

When setting the Tx power, the software retrieves the frequency, channel size, and antenna gain and generates a range of valid values from the minimum to the maximum possible. The indicated percentage value will be applied to this range and will output a valid single Tx power setting that will be saved to the configuration.

All of this is performed in the background, automatically eliminating all of the tedious work regarding compliance maintenance.