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Texas Instruments Debugging Communication Range Application notes
Application Report
SWRA603 – March 2018
Debugging Communication Range
Torstein Ermesjo
ABSTRACT
In a RF system having the best possible range is important in many cases. There are many factors that
can cause poor range. This application report provides a step-by-step guide on which parts of the design
could cause shorter range than desired.
Table 1. Definition of Terms
Term
Conducted
Radiated
CW
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2
3
4
5
6
7
Definition
The DUT is connected via cable directly to the instrument.
Over the air
Carrier Wave (tone)
Contents
Step 1: Calculate the Theoretical Range .................................................................................
Step 2: ........................................................................................................................
Step 3: Measure the Conducted Sensitivity .............................................................................
Step 4: Measure the Conducted Output Power..........................................................................
Step 5: Antenna Measurements ...........................................................................................
Step 6: Still Issues? .........................................................................................................
References ...................................................................................................................
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2
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3
3
3
4
Trademarks
SmartRF is a trademark of Texas Instruments.
All other trademarks are the property of their respective owners.
SWRA603 – March 2018
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Debugging Communication Range
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1
Step 1: Calculate the Theoretical Range
1
www.ti.com
Step 1: Calculate the Theoretical Range
1. Read Achieving Optimum Radio Range. This document describes the fundamental equations used to
estimate range and some of the most important factors that impact range.
2. Calculate line-of-sight (LOS) range using the excel sheet linked to Achieving Optimum Radio Range
with your radio settings.
a. Output power
b. Chip and data rate used
c. Heights of antennas above ground
d. Operating frequency
3. Are there any objects between the LOS of the transmitter and the receiver?
a. If yes, add a suitable absorption material that can represent the object blocking the LOS.
4. Choose an antenna gain that is realistic for your project.
a. Achieving 100% efficiency is not possible. Example: Typical efficiency would be – 4 dBi for a good
433 MHz antenna for a handheld product.
2
Step 2:
If the range is not meeting the expected distance based on the results in Step 1, the root cause needs to
be determined:
Poor range could be caused by one or more of the following factors:
• Poor sensitivity in the receiver
• Poor TX output power
• Poor antenna design (matching)
• Not optimal settings
The measurement methods depend on what type of equipment you have available.
It is highly recommend for the measurements to use SmartRF™ Studio to control the DUT. If that is not
possible, use unmodified settings and code from the software or unmodified code examples before testing
with the settings that are used for the product. This is to ensure that the testing of the hardware is done
with good known software.
3
Step 3: Measure the Conducted Sensitivity
1. Disconnect the antenna and perform conducted measurements at the SMA connector or solder a semirigid coax cable at the 50 Ω point.
2. Preferred: Use a signal generator that is capable of sending data packets. If the signal generator
cannot send data packets, just send preamble data.
3. If a signal generator is not available, use an EM/Launchpad as a transmitter. Use coax cables and
attenuation between the EM SMA connector and the 50 Ω point on the custom board.
NOTE: It is difficult to get an accurate number using this method since the exact values of output
power and attenuation are normally not known.
a. Some energy will also travel over the air from the EM to the DUT. In addition, background noise
could impact the results. To get more accurate results, the receiver should be placed in a shielded
box.
4. If the conducted sensitivity is poor:
a. Are the settings the same as the recommended values from SmartRF™ software? If the sensitivity
is good when using SmartRF Studio and not with the settings used for the project the settings has
to be evaluated.
b. What is the frequency difference between the DUT and the signal source? Ensure that the RF
frequency of the DUT sending a CW is as expected given the tolerance on the xtal used.
2
Debugging Communication Range
SWRA603 – March 2018
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Step 4: Measure the Conducted Output Power
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c. Is the schematic according to the reference design including all component values?
d. Is the layout according to the reference design?
4
Step 4: Measure the Conducted Output Power
1. Disconnect the antenna and perform conducted measurements at the SMA connector or solder on a
semi-rigid coax cable at the 50 Ω point.
2. Preferred: Use a Spectrum analyzer. MSP-SA430 or similar does not have the required accuracy. Use
1 MHz RBW for measuring output power and unmodulated carrier on the transmitter.
3. If a SA is not available, then use an EM or Launchpad with a SMA connection point.
a. Add a known RF attenuation block between the transmitter’s SMA connector (50 Ω point) and the
EM/Launchpad connector.
b. Use SmartRF Studio and set the EM/Launchpad in continuous RX and read the RSSI
4. If the conducted power is poor:
a. Is the schematic according to the reference design?
b. Is the layout according to the reference design?
5
Step 5: Antenna Measurements
If the conducted sensitivity and conducted output power are as expected, and the range is poor compared
to the estimated range, the antenna efficiency is likely poor. The required tuning is a function of the
ground plane size and the casing meaning that even if the antenna is copied directly from one of our
recommended antenna designs the tuning could be not optimal. The Antenna Measurements section in
the Antenna Selection Guide contains a more detailed description on how to measure antennas than the
summary below.
• Preferred: Use a Network Analyzer (VNA) to accurately tune the antenna. Some mini VNAs are
available on the market with a reasonable price tag if a full featured VNA is not available or cannot be
rented.
– Disconnect the radio and add a semi-rigid coax cable or SMA connector at the 50 Ω point towards
the antenna matching network and antenna.
– Compensate for the length of the semi-rigid cable or SMA with port extensions so they are not
included in the antenna measurements.
– Always measure the antenna in the final casing, otherwise the tuning will be invalid.
– Always measure the antenna as it would be used in the application. If the device is placed on a
metal shelf, the tuning must be made in a similar environment.
– Measure the resonance of the antenna and make sure the matching is better than VSWR 2.
– If the resonance is not correct or the matching is greater than VSWR 2, the antenna design has to
be reviewed again.
• If measurements with a VNA is not possible then use an EM or Launchpad with a known good
antenna.
– Measure the resonance frequency by sweeping the frequency of the transmitter; measure which
frequency the receiver reads as the highest RSSI.
6
Step 6: Still Issues?
If you still have issues post a question on E2E.
The minimum post on E2E must contain information about:
• Which chip was used
• Settings
• Software used
• Results from Step 1 through Step 5
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Debugging Communication Range
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3
References
7
References
•
•
4
www.ti.com
Antenna Selection Guide
Achieving Optimum Radio Range
Debugging Communication Range
SWRA603 – March 2018
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Copyright © 2018, Texas Instruments Incorporated
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