Fielding questions for wireless
manufacturers is one of the many activities that we perform at ACB. PACKETS
provides an overview of just a small portion of the communiqués that
run in and out of our office. This PACKETS focuses on unlicensed transmitters,
particularly digitally modulated devices
by far one of the more active
areas in wireless product launches.
Band edge correction factor: Is it possible to use a correction factor
for compliance with the Band Edges testing?
When a signal is pulse-modulated, a correction factor could be used per FCC
rule part 15.35. We must consider the worst-case duty factor in any 100 ms period
in any mode of operation. This correction factor could be used for example for
a DSSS transmitter, if one can prove that when the unit is set to a maximum
duty factor, it would not be exceeded due to the unit inherent function.
Co-located transmitters: What condition produces co-located transmitters
and what tests are required?
Co-located transmitters exist when two or more transmitters are installed less
than 20 cm apart and all transmitters transmit simultaneously. An MPE estimate
for mobile configurations is performed using the RF Exposure limits from OET
Bulletin 65: Evaluating compliance with FCC-Specified Guidelines for Human
Exposure to Radio Frequency Radiation, and Subpart I of Part 1 of the
47 CFR: Radio frequency radiation exposure limits and 47 CFR paragraph
2.1091: Radio frequency radiation exposure evaluation: mobile and unlicensed
devices. If either of the transmitters require SAR evaluation due to a portable
configuration, there will be additional considerations that must be taken into
account during this testing. For example, the area of highest SAR must be evaluated
twice. Once with the second transmitter turned on and again with it turned off.
SAR evaluation: We have a 2.4 GHz PCMCIA transmitter card that is used
in a portable configuration. Do we need SAR evaluation and can this device be
approved by a TCB?
Whether SAR evaluation is required depends on the peak output power (both conducted
and EIRP) and spacing between antenna and user under all expected applications.
(a) If the PCMCIA card is considered for use in a variety of host devices,
then < 2.5 cm operation must be assumed since devices such as a notebook
computers may be used while located in the users lap. To avoid SAR testing,
the peak conducted and EIRP levels must be less than 24 mW. If the conducted
or EIRP is greater than 24 mW the device will require SAR evaluation. SAR should
be evaluated with the transmitter installed in the slot(s) producing the maximum
SAR values. The minimum number of positions that must be evaluated for notebook
computers and body-worn PDAs are bottom-face of the host device in parallel
and in contact (0 cm) with flat phantom, and device perpendicular to phantom
with recommended spacing of 1.5 cm. If the peak conducted or EIRP output power
exceeds 100 mW, SAR testing will be required using a minimum of three hosts
within each platform type (i.e. three PDAs, three notebooks, etc.). TCBs
may approve these devices unless the peak output power (conducted or EIRP) exceeds
368 mW. Portable 2.4 GHz devices exceeding 368 mW may only be approved by the
(b) When the distance from the transmitting antenna is é 2.5 cm, the
device will require SAR when the peak conducted and EIRP level is é 49 mW. TCBs
may approve these devices unless the peak output power exceeds 368 mW (in which
case may only be approved by the FCC). Note that portable configurations may
only be classified as é 2.5 cm where it can be shown that the device can maintain
the 2.5 cm distance in all expected applications.
RF exposure evaluation: How does the FCC evaluate the RF exposure distance
for a steering beam antenna?
Classical equations are not appropriate for a steering beam antenna, due to
the beam, which is fully focused at the location of the intended receiver. The
surface power of the beam using phased array antennas is very low at the vicinity
of the antenna. However, the FCC is still considering an approach to calculate
the exposure distance for this type of antenna. Previously the FCC has accepted
the use of equation 11 given in OET Bulletin 65 for applications using such
antennas. Nonetheless, if you are developing a steering beam antenna, please
inform us about it. We could, on your behalf, contact the FCC and consider their
position depending on the antenna gain and the maximum power output of the unit.
The usual far field MPE estimation formula is probably not appropriate here.
OFDM: Is an OFDM (Orthogonal Frequency Division Multiplexing) device considered
a spread spectrum device?
Indoor and typical short-range RF communications in the unlicensed bands must
allow for multi-path fading and the presence of other unlicensed radios (and
interferers). The three main techniques for this requirement are: frequency
hopping, direct sequence (spreading techniques), and orthogonal frequency-division
multiplexing (OFDM). Although OFDM is similar to frequency hopping and direct
sequence, it is not technically a spreading technique. Transmitters operating
under FCC Part 15.247 have specific spreading requirements and the FCC recently
allowed OFDM to operate in the 2.4 GHz band as a DTS modulation type.
Question: OFDM Devices Continued
FCC Subpart C, Part 15.247 only covers 5725-5850 MHz bands. Where does
5150-5350 MHz spread spectrum/OFDM devices fit?
OFDM signal is considered as a type of spread spectrum signal. However, for
a unit that falls under the frequency band 5150-5350 MHz and 5725-5825 MHz,
this unit would have to meet 15.407 subpart E.
Question: UNII Devices
The freq band 5150-5350 MHz and 5725-5825 MHz bands are also covered under
the U-NII Subpart E, Part 15.401. Does this part cover spread spectrum devices?
OFDM modulation is considered as a part of 15.401 subpart E. This unit could
be tested and approved in the Spread spectrum band, but there is some restriction
for each band 5150-5250 MHz, 5250-5350 MHz, and 5725-5825 MHz, with respect
to the authorized power output, and antenna radio connectivity. If both UNII
and DTS approval are required, a composite application is necessary.
One of the requirements in this section is 15.401(d), wherein the transmitting
antenna shall be an integral part of the device.
Consider the following two cases:
Case 1: (Separate LAN Module + Separate Antenna Module) both integrated
inside a Laptop. Need to remove screws of laptop to see and get to the LAN &
AE modules. Fixed in laptop by manufacturer, and not portable by user.
Case 2: (Integrated LAN and AE module) inside a Laptop. Need to remove
screws of laptop to see and get to the integrated LAN & AE module.
Are both these cases acceptable under this section 15.401(d)? Are there any
special labeling requirements?
FCC Part 15.407(d) states precisely that the antenna should be an integral part
of the unit to avoid the changing or modification of the antenna to avoid any
interference. This area of the frequency spectrum is very sensitive as part
of the band is used by satellite communication. However the FCC has stated that
an antenna that attaches with a connector inside of the case is acceptable,
provided that there is no need for the users (or OEM integrators in the case
of modular approvals) to ever open the case. The antenna connector portion of
the product may only be accessible to the original manufacturer.
Regarding the label aspect, it would depend on whether the unit would be integrated
directly on the laptop and could be sold as a stand-alone. In the first configuration,
there should be a clear statement that a radio is installed in the laptop. In
the second configuration, the FCC ID should be listed on the unit itself.
New rules have been published
affecting the measurements and compliance of Cellular equipment (WT Docket No.
§22.917 Emission limitations for cellular equipment.
The rules in this section govern the spectral characteristics of emissions in
the Cellular Radiotelephone Service.
(a) Out of band emissions. The power of any emission outside of the authorized
operating frequency ranges must be attenuated below the transmitting power (P)
by a factor of at least 43 + 10 log(P) dB.
(b) Measurement procedure. Compliance with these rules is based on the
use of measurement instrumentation employing a resolution bandwidth of 100 kHz
or greater. In the 1 MHz bands immediately outside and adjacent to the frequency
block a resolution bandwidth of at least one percent of the emission bandwidth
of the fundamental emission of the transmitter may be employed. A narrower resolution
bandwidth is permitted in all cases to improve measurement accuracy provided
the measured power is integrated over the fully required measurement bandwidth
(i.e., 100 kHz or 1 percent of emission bandwidth, as specified). The emission
bandwidth is defined as the width of the signal between two points, one below
the carrier center frequency and one above the carrier center frequency, outside
of which all emissions are attenuated at least 26 dB below the transmitter power.
(c) Alternative out of band emission limit. Licensees in this service
may establish an alternative out of band emission limit to be used at specified
band edge(s) in specified geographical areas, in lieu of that set forth in this
section, pursuant to a private contractual arrangement of all affected licensees
and applicants. In this event, each party to such contract shall maintain a
copy of the contract in their station files and disclose it to prospective assignees
or transferees and, upon request, to the FCC.
(d) Interference caused by out of band emissions. If any emission from
a transmitter operating in this service results in interference to users of
another radio service, the FCC may require a greater attenuation of that emission
than specified in this section.
Amendment(s) published December 17, 2002, in 67 FR 77191
Effective date(s) February 18, 2003