Part 15 vs Part 97

You may read the full Code of Federal Regulation Documents for Part 15 HERE and Part 97 HERE.

Part 15 permits the existence of unlicensed “low signal” emissions and all of the regulations that they are subject to. Part 15 regulates power output by Signal Strength or Maximum Effective Isotropic Radiated Power (EIRP). As a result, you must consider both the Transmitter Output Power and the Antenna Gain for your project.

Part 97 augments section 15 and creates a tiered privilege system among a specific assortment of frequency bands. The three levels of privilege are Technician, General, and Extra. Each level unlocks specific frequency ranges and/or specific modes of operation. Additionally, Part 97 only regulates Transmitter Output, with no limitation upon antenna gain. However, there are other factors to keep in mind.

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Part 15: Radio Frequency Devices

Subpart C: Intentional Radiators is the section we will focus on below.

Within Subpart C are many stipulations and limitations for what we can and cannot do with Radio Frequency equipment. Sections 15.215 through 15.258 define various limits and conditions for specific frequency bands. A few of these are very common bands and are listed below:

15.239 Operation in the band 88-108 MHz.
15.240 Operation in the band 433.5-434.5 MHz.
15.243 Operation in the band 890-940 MHz.
15.245 Operation within the bands 902-928 MHz, 2435-2465 MHz, 5785-5815 MHz, 10500-10550 MHz, and 24075-24175 MHz.
15.247 Operation within the bands 902-928 MHz, 2400-2483.5 MHz, and 5725-5850 MHz.
15.249 Operation within the bands 902-928 MHz, 2400-2483.5 MHz, 5725-5875 MHZ, and 24.0-24.25 GHz.

Sections 245, 247, and 249 differ in how the equipment in the overlapping bands behave.

Section 245(a): Operation under the provisions of this section is limited to intentional radiators used as field disturbance sensors, excluding perimeter protection systems.

Section 247(a): Operation under the provisions of this Section is limited to frequency hopping and digitally modulated intentional radiators…

Section 249(b): Fixed, point-to-point operation as referred to in this paragraph shall be limited to systems employing a fixed transmitter transmitting to a fixed remote location. Point-to-multipoint systems, omnidirectional applications, and multiple co-located intentional radiators transmitting the same information are not allowed…

Section 245, 247, and 249 also differ in the authorized power output.

Essentially, for most cases you are limited to 1 Watt (30 dB) of transmit power plus a 6dB antenna gain. As antenna gain goes up, transmit power must go down to maintain the 36dB radiated power limit.

Section 245(b):
The field strength of emissions from intentional radiators operated within these frequency bands shall comply with the following:

Section 247(b):
The maximum peak conducted output power of the intentional radiator shall not exceed the following:

(1) For frequency hopping systems operating in the 2400-2483.5 MHz band employing at least 75 non-overlapping hopping channels, and all frequency hopping systems in the 5725-5850 MHz band: 1 watt. For all other frequency hopping systems in the 2400-2483.5 MHz band: 0.125 watts.

(2) For frequency hopping systems operating in the 902-928 MHz band: 1 watt for systems employing at least 50 hopping channels; and, 0.25 watts for systems employing less than 50 hopping channels, but at least 25 hopping channels, as permitted under paragraph (a)(1)(i) of this section.

(3) For systems using digital modulation in the 902-928 MHz, 2400-2483.5 MHz, and 5725-5850 MHz bands: 1 Watt. As an alternative to a peak power measurement, compliance with the one Watt limit can be based on a measurement of the maximum conducted output power. Maximum Conducted Output Power is defined as the total transmit power delivered to all antennas and antenna elements averaged across all symbols in the signaling alphabet when the transmitter is operating at its maximum power control level. Power must be summed across all antennas and antenna elements. The average must not include any time intervals during which the transmitter is off or is transmitting at a reduced power level. If multiple modes of operation are possible (e.g., alternative modulation methods), the maximum conducted output power is the highest total transmit power occurring in any mode.

(4) The conducted output power limit specified in paragraph (b) of this section is based on the use of antennas with directional gains that do not exceed 6 dBi. Except as shown in paragraph (c) of this section, if transmitting antennas of directional gain greater than 6 dBi are used, the conducted output power from the intentional radiator shall be reduced below the stated values in paragraphs (b)(1), (b)(2), and (b)(3) of this section, as appropriate, by the amount in dB that the directional gain of the antenna exceeds 6 dBi.

Section 249(a):
Except as provided in paragraph (b) of this section, the field strength of emissions from intentional radiators operated within these frequency bands shall comply with the following:

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Part 97: Amateur Radio Service

Part 97 is an extensively detailed section due to it’s tight regulation of who/what/where/when/why. As a licensed operator, it is beneficial to know most of the regulations that are applicable (hint: many of them are on the licensure exam). For simplicity, only the ones directly contrasting Part 15 or relatable to telecommand/remote control will be detailed below.

Subpart B

Subpart B allows telecommand and telemetry but does not allow encrypted systems, as well as declares identification properties:

97.111 Authorized transmissions.
97.113 Prohibited transmissions.
97.119 Station identification.

97.111(b): In addition to one-way transmissions specifically authorized elsewhere in this part, an amateur station may transmit the following types of one-way communications:
(3) Telecommand;
(7) Transmissions of telemetry.

97.113(a): No amateur station shall transmit:
(4) …messages encoded for the purpose of obscuring their meaning, except as otherwise provided herein…

97.119(a): Each amateur station, except a space station or telecommand station, must transmit its assigned call sign on its transmitting channel at the end of each communication, and at least every 10 minutes during a communication, for the purpose of clearly making the source of the transmissions from the station known to those receiving the transmissions. No station may transmit unidentified communications or signals, or transmit as the station call sign, any call sign not authorized to the station.

97.119(b): The call sign must be transmitted with an emission authorized for the transmitting channel in one of the following ways:
(3) By a RTTY emission using a specified digital code when all or part of the communications are transmitted by a RTTY or data emission;
(4) By an image emission conforming to the applicable transmission standards, either color or monochrome, of § 73.682(a) of the FCC Rules when all or part of the communications are transmitted in the same image emission

Subpart C

Meanwhile, Subpart C specifies what a specific station is and how it may behave. This is the most important section for our needs, as it gives the exemption to 97.113(a)(4).

One key thing is missing however: First Person Video systems are not specifically called out here. As a result, 97.119(b)(4) applies for any video transmitter. This is typically taken care of by adhering or writing one’s call sign within the field of view of the camera. Note that this may be easier said than done for a PTZ type camera.

In contrast to Part 15, note that 97.215(c) only specifies transmitter power of 1 Watt. As such, a high gain antenna can make that work in one’s favor.

Finally, though 97.215(a) exempts identification, when using UART/Serial communication from a microcontroller it is generally encouraged to put the operator’s callsign in the command string going to the modem.

97.215 Telecommand of model craft.
97.217 Telemetry.

97.215 Telecommand of model craft:
An amateur station transmitting signals to control a model craft may be operated as follows:
(a) The station identification procedure is not required for transmissions directed only to the model craft, provided that a label indicating the station call sign and the station licensee’s name and address is affixed to the station transmitter.
(b) The control signals are not considered codes or ciphers intended to obscure the meaning of the communication.
(c) The transmitter power must not exceed 1 W.

97.217 Telemetry:
Telemetry transmitted by an amateur station on or within 50 km of the Earth’s surface is not considered to be codes or ciphers intended to obscure the meaning of communications.

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What the difference means

For Part 15 Wireless Communications, RP-SMA xBee’s are the Go-To tool, but an alternative option is the RF Designs 900X.

xBee Pro 900HP Specifications:
250 mW (24 dBm) @ 902-928 MHz, which allows for 12dB of antenna gain.
Receive Sensitivity is ~ 100 dBm

xBee 3 Pro Specifications:
80 mW (19 dBm) @ 2400-2483 MHz, which allows for 17dB of antenna gain.
Receive sensitivity is ~ 100 dBm

RFD 900X Specifications:
1000 mW (30 dBm) @ 902-928 MHz, which allows for 6dB of antenna gain under Part 15.
Receive sensitivity is ~120 dBm

BUT, if you have your FCC license, then you also have rights to that same 902-928 MHz band.  Because Part 97 only cares about PEP and not EIRP, you can put a high gain antenna on the radio – take that same 1 watt (30 dBm) and throw a 18dB Parabolic Dish antenna on it for 48 dB total. Perfectly legal.

36dB versus 48dB of transmit power can make a big difference in some scenarios.