Application Note AN002 - LSR Note AN002 ... This ISM band and modulation technique while amplified...

Application Note AN002

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FCC Primer for Amplified 802.15.4 / 2.4GHz DSSS Applications

An Article by Jason Olson Sr. RF Engineer at LS Research

Abstract

This application note focuses on FCC compliance limits for

2.4GHz DSSS radios being utilized in ZigBee‐compliant and

non‐ZigBee‐compliant DSSS platforms.

Integrated 2.4GHz transceivers and SoC (System on a Chip)

radios allow engineers to quickly implement radio designs

following manufacturers’ data sheets and application

notes. Application‐specific PAs and integrated RF “front

ends” also enable increased performance by mating a PA

or various combinations of integrated balun, PA, LNA and

T/R switch to the single‐chip radio. This produces a simple

yet powerful design.

The FCC limits stated in 47CFR 15.247 allow for a

maximum of 1W conducted RF power output and up to a

+6dBi antenna gain. This document will outline significant

limitations in achieving TX output power to assist the

engineer in investigating relevant factors before bringing

the product to the certification lab.


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Contents Abstract: ....................................................................................................................................................... 1

1 Introduction ...................................................................................................................................... 3‐4

2 Background and Conducted Bench Tests ......................................................................................... 4‐6

3 15.247 Applicable RF Limits ................................................................................................................. 6

3.1 Upper Band Edge Limits and FCC Restricted Bands ..................................................................... 6‐8

3.2 Lower Band Edge Limits ............................................................................................................ 8‐9

3.3 Spurious and Harmonic Limits ................................................................................................ 9‐10

3.4 Harmonic Emissions, Filtering, and Shielding ........................................................................... 11

3.5 Duty Cycle Relaxation ........................................................................................................... 12‐13

3.6 Required Axis Scans .............................................................................................................. 13‐14

3.7 Power Spectral Density (PSD) ............................................................................................... 14‐15

3.8 Occupied Bandwidth (BW) ........................................................................................................ 15

3.9 Conducted Output Power .......................................................................................................... 16

4 15.247 Conducted Limit Summary .................................................................................................... 17

5 Compliance Pre‐Scan .......................................................................................................................... 18

6 Conclusions ........................................................................................................................................ 19

7 Abbreviations and Definitions ........................................................................................................... 20

8 Document History .............................................................................................................................. 20

9 Document References ....................................................................................................................... 20

10 Company Information .................................................................................................................... 21

�


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1 Introduction

The outlined information focuses on FCC compliance aspects of industry offerings in

the 2.4GHz ISM band utilizing Direct Sequence Spread Spectrum (DSSS) at 250kbps.

This ISM band and modulation technique while amplified (greater than about ‐

1.75dBm transmit power output per 15.249) applies FCC limits largely defined

under section 47CFR 15.247. These limits state a maximum conducted output

power of 1 watt in the 2.4GHz ISM band. Other applicable rules are defined in parts

15.35, 15.205, 15.207 and 15.209. This document summarizes these limits to reflect

aspects that can further limit transmit power in the design.

The 802.15.4 (ZigBee) channel allocation consists of 16 channels numbered 11 to

26, starting at 2.405GHz (CH‐11) and ending at 2.480GHz (CH‐26). Bandwidth is

5MHz per channel. The allocated spectrum spans from 2.4000GHz to 2.4835GHz.

Channel numbering, which starts at channel 11, is a continuation of applied

standards in the 900MHz ISM band.

Figure 1: 802.15.4 Channel Spectrum

Figure 1 shows how the 802.15.4 channels co‐exist with the three non‐overlapping

Wi‐Fi (802.11) channels. Note the independence of channels 15, 20, 25 and 26.

Channels 25 and 26 in this application are favored by system designers to help

avoid known potential interference. The ultimate utility of these higher channels is

compromised when increased output power is required.

802.15.4 transceivers are available from a number of chip vendors, such as

Freescale Semiconductor, Ember and Texas Instruments. In addition to these single


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chip transceivers, there are a variety of PAs, LNA and PA/LNA integrated devices

that specifically cater to these applications.

With any power amplifier practically implemented in this application, the limits

across the band will be significantly lower than the 1W conducted due to

constraints outlined in Section 3.

2 Background and Conducted Bench Tests

Since this document is designed to assist the engineer on the bench, it is important

to be able to relate field‐strength units with power.

An electric field in free space can be expressed as:

where (P) is watts, (E) is field strength in microvolt per meter, and the distance (D) is in meters. The 377 term is the characteristic impedance of free

space.

This equation assumes an ideal isotropic antenna with its power spread evenly

across a sphere, with a radial distance given by (D).

The equation is converted from watts to mW (to reference dBm), and the distance

is defined as 3 meters since most limits per 47CFR 15.247 are performed as field

strength at 3m.

P (dBm) = 20 Log (E) – 95.229

If field strength is stated in dBuV/m, then the 20 Log E term (uV/m) can be

substituted for the dBuV/m term.

A full derivation from free‐space impedance and power density in several equations

can be simplified into a single handy statement: ~95dBuV/m @ 3 meters equates to

0dBm conducted output power (assuming the antenna is isotropic and has a gain of

one or 0dBi). Known antenna gain and directional characteristics can be used to

offset the field strength term for adjustment.


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For example, a 3‐meter field strength measurement of 110dBuV/m would equate to

+15dBm conducted power at the antenna port with an antenna gain of 0dBi. The

engineer should expect +12dBm in conducted measurement at the antenna port

given the same with a +3dBi antenna.

Likewise, a restricted band limit (see Section 3) of +54dBuV/m at 3m can be

calculated as:

54dBuV/m – (95dBuV/m) = ‐41dBm EIRP. EIRP (effective isotropic radiated power)

simply implies that the antenna is absolutely uniform in gain in all directions. As no

antenna is truly isotropic, the intended utilization of design applies to the method

of FCC certification (e.g., Duty Cycle Relaxation, Section 3.5).

All field strength references in this document are in dBuV/m at 3meters.

Conducted RF measurements can be performed on the lab bench to evaluate band

edge power and relative limits in other sections of this document. The DUT can be

cabled to a spectrum analyzer through a variable or fixed RF attenuator(s). The

input power to the spectrum analyzer should not exceed ‐20dBm to prevent

creating inter‐modulation products in the spectrum analyzer and resultant error in

measurement.

Figures 2 and 3 give a basic test setup for measuring conducted emissions. The RF

attenuator value is specific to the DUT’s output to achieve the desired input power

to the spectrum analyzer.

Figure 2: Block Diagram of Conducted Lab Bench Measurements


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RECOMMENDED SPECTRUM ANALYZER MEASUREMENT SPECIFICATIONS

SPECIFICATION VALUE

RBW 100kHz

VBW 300kHz

DETECTOR PEAK

TRACE MAX HOLD

Figure 3: Recommended SA Settings for Sections 3.1, 3.2, 3.3 and 3.4

Spectrum analyzer settings that deviate from the above are noted in other sections.

The limits defined in Sections 3.1‐3.4 for a 15.247 device (>1GHz) refer to

conducted measurements using an average detector. From FCC section 15.35(b),

peak limits (utilizing a peak detector) are also limited to 20dB over the average

limit. Measurements utilizing both average and peak detectors are recommended in

initial bench analysis.

3 15.247 Applicable RF Limits

Section 3 outlines the various FCC limits and restrictions applicable to an 802.15.4

device filed under FCC part 15.247. Some of the limits are absolute (Sections 3.7‐

3.9) and some can be varied by applying a duty cycle relaxation factor (applicable to

Sections 3.1‐3.4 and defined in Section 3.5).

3.1 Upper Band Edge Limits and FCC Restricted Bands

The (16) 802.15.4 channels are not centered within the specified bandwidth.

Channel 11’s (Figure 1) center frequency or fundamental is 5 MHz from the lower

band edge. With a 5 MHz channel bandwidth (BW), the lower band edge is

therefore 2.5 MHz away from channel 11. Channel 26’s center frequency is 3.5 MHz

from the upper band edge. The upper band edge is 1.0MHz away from channel 26

given the specified 5 MHz channel BW.


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The FCC further limits RF energy allowed into defined restricted bands. The defined

2.4GHz band resides between two restricted bands with an average limit of 54

dBuV/m. The upper band edge is directly adjacent to a restricted band. These

restricted bands are given from 2 GHz to 24 GHz in Figure 4. Restricted bands

adjacent to the 2.4GHz ISM band are shown in bold text. Higher frequency

restricted bands are also an issue in amplified designs (see Section 3.4).

MHz GHz

2200‐2300 7.25‐7.75

2310‐2390 8.025‐8.5

2483.5‐2500 9.0‐9.2

2655‐2900 9.3‐9.5

3260‐3267 10.6‐12.7

3332‐3339 13.25‐13.4

3345.8‐3358 14.47‐14.5

3600‐4400 15.35‐16.2

4500‐5150 17.7‐21.4

5350‐5460 22.01‐23.12

23.6‐24.0

Figure 4: FCC Restricted Bands 2 GHz ‐ 24 GHz

Restricted bands are outlined in FCC part 15.205.

Figure 5 shows a modulated 802.15.4 signal at 250kbps. The center of the vertical

grid lines is the upper band edge. Note that the modulated envelope is wider on the

bottom; increasing the fundamental transmit power also increases RF energy

outside the channel BW into the restricted band.


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Figure 5: Upper Band Edge

The band edge limit is exceeded by 6dB in the Figure 5 example. Output power on

channel 26 is usually limited under 95dBuV/m or 0dBm for a constant transmission.

Amplified designs often cannot utilize this channel in utility despite its desired place

outside of Wi‐Fi. Practical design modifications such as additional filtering are

ineffective given the close proximity of the signal to the band edge. Any filter that

offered sufficient attenuation at the band edge would also reject part of the

intended signal.

Section 3.5 outlines relaxed limits due to duty cycle relaxation with periodic

transmissions that may be applicable to this section.

3.2 Lower Band Edge Limits

The upper band edge posed a limit on transmit power in the previous section; the

lower band edge will also limit transmit power on channel 11 to a lesser extent.

Recall that the specified channels are offset in the band.

1) The lower band edge is an additional 1.5MHz away from the channel 11

fundamental vs. the upper band edge to channel 26.

2) The adjacent restricted band is also 15MHz below the lower band edge.


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Figure 6: Lower Band Edge Plot

Even though the lower band edge is 15MHz (3x the channel bandwidth) below the

fundamental, the restricted band limit will apply before the band edge limit of

20dB below the fundamental. This is demonstrated in Figure 6, where the band

edge is >40dB below the fundamental but the restricted‐band limit is met.

Notice that in Figure 6, the band edge is slightly over the limit indicated by the red

line. Output power on channel 11 is usually limited under 113dBuV/m or +18dBm

for a constant transmission. This channel may be dropped or utilized at a lower

transmit power if the system design allows.

Section 3.5 outlines relaxed limits due to duty cycle relaxation with periodic

transmissions that may be applicable to this section.

3.3 Spurious and Harmonic Limits

Spurious and harmonic emissions are defined as unwanted emissions outside the

intentional signal. Restricted band limits are referenced in part 15.205 and defined

in part 15.209. For 15.247 devices, emissions outside of any restricted band use a

limit relative to the fundamental defined by:

A 20dB difference of maximum power between the fundamental and the

unintentional emission measured within a 100 kHz BW


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See FCC section 15.247(d) for definition on the limit stated above. Sections 3.1 and

3.4 define 15.247 limits within restricted bands.

One matter of concern is spurs offset from the fundamental by the reference

oscillator (e.g., 26MHz, 32MHz). These spurs may reside on adjacent restricted

bands and limit output power on channels other than 11 and 26. These spurs can

be noted in conducted measurement with a spectrum analyzer.

Spurious emissions not related to harmonics of the fundamental may not apply

the duty cycle correction factor outlined in Section 3.5. A good rule of thumb is to

place the DUT in receive mode on the same channel (frequency) if the spur

remains; a duty cycle correction factor may not be applied.

Figure 7: Example of Spurious Noise Offset from Unmodulated Carrier

Spurious emissions may also be outlined in the SoC manufacturer’s data sheet.


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3.4 Harmonic Emissions, Filtering and Shielding

Harmonics usually are caused by non‐linearity in the construction of the signal and

the PAs used to amplify. In the context of this document, the signal is amplified

internally to the chosen IC (often to 0dBm) and then again externally to reach the

system design goals.

Channel 11’s second harmonic has an average limit of 54dBuV/m, as it is in an FCC‐restricted band. The second and third harmonics of channel 18 (mid‐channel) and channel 25 also fall into restricted bands. Measurements are required to the 10th harmonic of each scanned channel (low, mid and high channel). In contrast to all previous sections, conducted and antenna radiated harmonic

emissions can be controlled by the engineer in hardware design by implementing

a low‐pass filter. Higher order harmonics likely can radiate off the PCB before this

additional filtering and antenna. The following design rules can help:

1) If a shield is implemented, place its boundaries over the entire circuitry,

including the final output filtering.

2) Ensure uninterrupted RF ground and supply decoupling.

3) Route all radio control traces into an inner PCB layer (e.g., PCB layer 3) not

interrupting the ground under the RF microstrip (e.g., PCB layer 2). Examples

of these RF control traces include the LNA and PA enable or bias and T/R

control. Connect back to the component layer with via close to the

component, with #4 below.

4) Place low ESR, in‐band bypass capacitors (e.g., 8pF) near the connection

point of all radio I/O control lines.

5) Ensure that all bypass capacitors have a good connection to ground by

utilizing at least three ground vias close to the component’s PCB ground pad.

Utilize the bottom layer and inner layer grounds with vias.

6) “Stitch” the PCB edge perimeter with vias tying together the PCB ground

planes, especially on small PCBs with RF traces close to the PCB edge.

7) With increased output power and amplifier characteristics, ensure that the

filtering provides adequate rejection up to the higher harmonics by

evaluating its response or the SRF of the discrete components.

Emissions radiated pre‐filter from the device are difficult to evaluate on the

bench. An FCC pre‐scan is recommended to evaluate all radiated emissions from

the device.


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3.5 Duty Cycle Relaxation

All previous sections assume a 100% duty cycle within stated FCC limits. The field

strength limits, in measurement, are a product of an average detector. For

periodic transmissions, a peak detector can be utilized with an associated

relaxation on the peak values. The calculated relaxation factor is applied to the

peak measurement to derive the average value. This correction can be applied to

both the fundamental and all associated harmonics.

This relaxation factor is calculated as:

RF [dB] = 20 log (TX ON [mS]/100mS)

Any relaxation is limited to 20dB. A 20dB relaxation factor equates to only a 10%

duty‐cycle or 10mS transmission within any 100mS window. ZigBee‐compliant

radios implement under a 50% duty cycle and thus an inherent ~6dB relaxation

factor. This can be applied to band edge limits of Section 3.1 and 3.2.

Applicable relaxation factor is defined in FCC 15.35(c).

This is important to note as the DUT is prepared for a trip to the compliance lab.

The test firmware should support the maximum duty cycle the product will see in

the field to evaluate benefit. Often the hardware is only exercised by a chip

manufacturer’s test tool and is not specific to the end application.

Figure 8 outlines recommended spectrum analyzer settings to determine the duty

cycle and inherent correction factor. The center frequency is set to the

fundamental frequency, and the frequency span is set to ZERO. The sweep time

determines the window of observation in the time domain, like an oscilloscope.


SPECIFICATION VALUE

RBW 1MHz

VBW 5MHz

DETECTOR PEAK

TRACE MAX HOLD

SWEEP TIME 100mS

SPAN ZERO

Figure 8: Recommended SA Settings for Duty Cycle Calculation


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Figure 9 provides an example plot of a periodic transmission within a 100mS

window. The transmit time is measured and multiplied by the number of equal

transmit events within 100mS. The sweep time can be shortened to better

resolution on a single transmit pulse. If the pulses are unequal, each transmit

pulse in the 100mS duration should be measured and summed.

Figure 9: Example Duty Cycle Plot

3.6 Required Axis Scans

If the device is to be implemented in a single orientation, only a single axis scan is

required. An example of this would be a tabletop or wall‐mounted device.

If the device is mobile, portable or body‐worn, three axis of scans are required for

all radiated measurements. Three axis of scans are defined by 360‐degree rotation

of the DUT placed in three different azimuthal planes, recording both vertical and

horizontal polarizations. Figure 10 provides an example of three axis of scans or

the required orientation of the same DUT on a fixed turntable.


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Figure 10: DUT Orientation on a Turntable for Three‐Axis Scan

3.7 Power Spectral Density

Power spectral density (PSD) is the power or energy distributed across a defined

bandwidth or across frequency. The power spectral density conducted from the

antenna port shall not be greater than 8dBm in any 3 kHz band per 15.247(e).

Figure 11 notes recommended spectrum analyzer settings when performing this

conducted measurement.


SPECIFICATION VALUE

RBW 3kHz

VBW 10kHz

DETECTOR PEAK

TRACE MAX HOLD

SWEEP TIME 500s

SPAN 1.5MHz

Figure 11: Recommended SA Settings for PSD Measurement

PSD was measured on an 802.15.4‐compliant radio with an output power of

0dBm. Figure 11 utilizing an 802.15.4 design exhibits a peak PSD of ‐14dBm in any

3kHz BW from a conducted output power of 0dBm. Since the modulation

envelope should be fixed, a 1:1 correlation from increased power output should

be expected. Therefore, a 802.15.4 design is expected to be limited to a

conducted output power of +22dBm due to the PSD limit.


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Figure 12: PSD Measurement Example

‐14dBm (measured) + 8dBm (limit) = 22dBm

0dBm (per Figure 11) + 22dBm = 22dBm conducted power output to PSD limit

3.8 Occupied Bandwidth

Since the modulation and data rate are fixed in the transceiver, the occupied bandwidth (BW) is defined as the modulation type and data rate inherent to the core SoC radio. FCC section 15.247 (a) (2) states that the minimum 6dB bandwidth shall be at least 500kHz. With a properly operating 802.15.4 radio, this FCC limit should pose no compliance issues.


SPECIFICATION VALUE

RBW 100kHz

VBW 300kHz

DETECTOR PEAK

TRACE MAX HOLD

SWEEP TIME 5mS / Auto

SPAN 3‐6MHz

Figure 13: Recommended SA Settings for Occupied BW Measurement


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Figure 14: Example Measurement of Occupied BW

3.9 Conducted Output Power

Conducted output power is simply the original +30dBm specified limit per 15.247

(b). Figure 15 outlines recommended spectrum analyzer settings for performing

the measurement on the bench. The previous sections outline defined limits that

dominate in limitation of allowed transmit power.


SPECIFICATION VALUE

RBW 5MHz

VBW 10MHz

DETECTOR PEAK

TRACE MAX HOLD

SWEEP TIME 5mS

SPAN 25MHz

Figure 15: Recommended SA Settings for Conducted Output Measurement


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4 15.247 Conducted Limit Summary

Figure 16 summarizes Section 3 to assist the engineer in bench evaluation.

Test 15.247 Restricted Band Limit

Calculated Conducted Restricted Band Limit

15.247 Non‐Restricted Band Limit

Duty‐Cycle Relaxation Allowed?

Upper Band Edge (2.480 GHz)

54dBuV/m average

detector @ 2.4835 GHz

‐41dBm Ave ‐21dBm Peak @ 2.4835

GHz

N/A; upper band edge is near

restricted band

Defined as 20dB below fundamental

@ 2.480 GHz

Yes

Lower Band Edge (2.405 GHz)

54dBuV/m average

detector @ 2.390 GHz

‐41dBm Ave ‐21dBm Peak @ 2.390 GHz

N/A; upper band edge is near

restricted band

Defined as 20dB below fundamental

@ 2.405 GHz

Yes

Spurious* 54dBuV/m average detector

‐41dBm Ave ‐21dBm Peak

20dB below fundamental

No*

Harmonics to 24.8GHz

54dBuV/m average detector

‐41dBm Ave ‐21dBm Peak

20dB below fundamental

Yes

PSD N/A, in band 8dBm in 3kHz BW No

Occupied BW

N/A, in band Minimum of 500kHz in 6dB BW

N/A

Output power

N/A, in band 1W/ 30dBm No

*Spurious emissions not related to the fundamental (i.e., local oscillator

reference spurs). Figure 16: Limits Applicable to 802.15.4 Devices Filed Under FCC 15.247


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5 Compliance Pre‐Scan

A pre‐scan at the compliance lab can determine issues with harmonics, spurious

emissions, other unintentional radiation, line‐conducted issues or the operation of

the test modes. This initial feedback can help the design engineer evaluate

necessary changes. The optimal time for a pre‐scan is when the hardware is

mature with minimum PCB rework (jumper wires and cut traces) and before the

final “pilot” revision. This allows all potential issues to be addressed before the

final revision and scheduling a full scan. Most design cycles are scheduled within a

fixed number of revisions to product release. A pre‐scan will often reduce internal

costs by addressing previously unknown issues before the final scheduled revision.

Before a device is submitted, the following information should be prepared to

allow the lab to determine required tests and correctly manipulate the submitted

DUT.

1) Provide a short description of the technology: what it is, how it will be used,

and its purpose.

2) Specify how the device is powered: battery and type, AC, DC, wall transformer,

supplied voltage, and so on.

3) Is the device fixed, mobile, or integrated into another system?

4) What channels are utilized? 5) What is the maximum power output? Is the power output variable per

channel? Is the power output fixed but varying across channels? Specify the operation per each channel.

6) What antennas are used and supplied, and what is the specified antenna gain? 7) The unit should be able to exhibit a constant transmit mode to ensure that all

emissions are captured during DUT rotation. 8) The unit should be able to exhibit a pulsed transmit mode representative of

production utility to allow evaluation of the maximum duty cycle of the device and any inherent relaxation to the compliance limits.

9) Is there any cabled communication to the device?

10) Is there a pre‐existing FCC filing for the device?

11) Is the device intended for filing as a module?

12) Will the device be offered in differing variants? Specify any changes to the

device, even those that are non‐RF.

13) How does the EMC engineer exercise the operating and test modes? What

mode(s) are required for each channel?


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6 Conclusions

An amplified 802.15.4 radio requires some background on FCC certification that can

affect initial system design, PCB design, data through‐put, amplifier choice,

shielding, channel allocation and required output filtering.

Investing in an abbreviated compliance pre‐scan with mature hardware before

conducting a ”final” design revision without knowledge of potential FCC issues will

bring the product to the production level, saving cost and time.


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7 Abbreviations and Definitions

SoC “System on a Chip,” defined as a combined radio transceiver and microcontroller

PA Power amplifier for increasing transmit power

DSSS Direct Sequence Spread Spectrum

dBi dB relative to a theoretical isotropic antenna. A 0dBi antenna has no gain or loss.

Front‐End The RF components between the SoC and the antenna

LNA Low noise amplifier for increasing receive gain and sensitivity

Balun A transformer device for impedance matching a differential signal path to single‐ended

T/R switch An RF switch for directing the signal along the transmit or receive paths

Spurs Unwanted emissions outside the intentional signal, excluding harmonics

Harmonics Inter‐modulation products due to non‐linearity of devices

EIRP Effective isotropic radiated power: A field‐strength‐derived value for conducted power assuming an isotropic antenna

SRF Self resonant frequency: the frequency at which parasitic reactance exceeds the intentional

Isotropic Uniform response in all directions

LPF Low pass filter: attenuates frequencies above the pass‐band

BW Bandwidth: the product within a defined span of frequency

PSD Power spectral density: power within a defined bandwidth

RBW Resolution bandwidth: determines the limit in frequency BW that can be resolved

VBW Video bandwidth: determines the limit in frequency BW that can be displayed

8 Document History

Revision Date Description/Changes

1.0 09‐07‐09 Feedback from EMC ENG

1.5 09‐29‐09 Detail on conducted meas.

2.0 10‐07‐09 Initial Release

2.5 10‐12‐09 Edits & missing Diagrams

9 Document References

Document Reference/Date

Code Of Federal Regulations CFR 47, Parts 0 to 19

http://edocket.access.gpo.gov/cfr_2008/octqtr/pdf/47cfr15.247.pdf


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10 Company Information

Headquarters LS Research LLC W66 N220 Commerce Court Cedarburg, WI 53012 Phone: 262‐375‐4400 Fax: 262‐375‐4248 Web site: http://www.lsr.com

Regional Office LS Research LLC 5520 Nobel Drive, Suite 175 Madison, WI 53711 Phone: 262‐375‐4400 Fax: 262‐375‐4248 Web site: http://www.lsr.com

U.S. Sales Offices East Coast Sales Jennifer Fishbein Director of East Coast Sales Phone: 262‐228‐7868 E‐mail: [email protected]

Midwest Sales Ryan Plach Director of Midwest Sales Phone: 262‐228‐7865 E‐mail: [email protected]

West Coast Sales Peter J. Mayhew Director of West Coast Sales Phone: 262‐546‐1731 E‐mail: [email protected]

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Application Note AN002 - LSR Note AN002 ... This ISM band and modulation technique while amplified...

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