NEO-D9S - Integration manual
• In-band interference: Although the L-band band is kept free from intentional RF signal sources
by radio-communications standards, many devices emit RF power into the L-band band at
levels much higher than the L-band signal itself. One reason is that the frequency band above
1 GHz is not well regulated with regards to EMI, and even if permitted, signal levels are much
higher than L-band signal power. Notably, all types of digital equipment, such as PCs, digital
cameras, LCD screens, etc. tend to emit a broad frequency spectrum up to several GHz of
frequency. Also wireless transmitters may generate spurious emissions that fall into L-band
band.
As an example, GSM uses power levels of up to 2 W (+33 dBm). The absolute maximum power input
at the RF input of the L-band receiver can be +15 dBm. The GSM specification allows spurious
emissions for GSM transmitters of up to +36 dBm, while the L-band signal is less than -128
dBm. By simply comparing these numbers it is obvious that interference issues must be seriously
considered in any design of a L-band receiver. Different design goals may be achieved through
different implementations:
• The primary focus is to prevent damaging the receiver from large input signals. Here the L-
band performance under interference conditions is not important and suppression of the
signal is permitted. It is sufficient to just observe the maximum RF power ratings of all of the
components in the RF input path.
• L-band performance must be guaranteed even under interference conditions. In such a case,
not only the maximum power ratings of the components in the receiver RF path must be
observed. Further, non-linear effects like gain compression, NF degradation (desensitization)
and intermodulation must be analyzed.
Pulsed interference with a low-duty cycle such as GSM may be destructive due to the high
peak power levels.
4.6.2 In-band interference mitigation
With in-band interference, the signal frequency is very close to the L-band frequency. Such
interference signals are typically caused by harmonics from displays, micro-controller operation, bus
systems, etc. Measures against in-band interference include:
• Maintaining a good grounding concept in the design
• Shielding
• Layout optimization
• Low-pass filtering of noise sources, e.g. digital signal lines
• Remote placement of the L-band antenna, far away from noise sources
• Adding an LTE, CDMA, GSM, WCDMA, BT band-pass filter before antenna
4.6.3 Out-of-band interference
Out-of-band interference is caused by signal frequencies that are different from the L-band carrier
frequency. The main sources are wireless communication systems such as LTE, GSM, CDMA,
WCDMA, Wi-Fi, BT, etc.
Measures against out-of-band interference include maintaining a good grounding concept in the
design and adding a L-band band-pass filter into the antenna input line to the receiver.
For GSM applications, such as typical handset design, an isolation of approximately 20 dB can be
reached with careful placement of the antennas. If this is insufficient, an additional SAW filter is
required on the L-band receiver input to block the remaining GSM transmitter energy.
UBX-19026111 - R07
4 Design
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C1-Public
