Wavenet Technology Pty Ltd. BM2900D Benutzerhandbuch
APPENDIX F – Guide to Desense ______________________________ Boomer II User Manual & Integrator’s Guide
Copyright Wavenet Technology © November 2003
138
BM210012WT37
device if it is within 30 meters of the device, assuming that an emission
exists at the channel frequency of the radio.
Networks can assist in the desense problem by offering more than one
channel frequency at which to operate. If the radio encounters
interference on a channel, it can then roam to another.
WAN protocols include retry mechanisms that resend messages not
acknowledged from the subscriber device. These protocols can correct
problems from intermittent noise sources by retrying during a time slot
that does not coincide with noise source interference.
At a certain point, desensitising a wireless modem receiver creates
unacceptable coverage in the network. This usually is in the 10dB
range, though it can vary with networks.
The integrator should consult the technical staff at their target network
for any minimum RF desense performance levels and related
measurement methods that may be required for the device to be
accepted for customer use on that network.
exists at the channel frequency of the radio.
Networks can assist in the desense problem by offering more than one
channel frequency at which to operate. If the radio encounters
interference on a channel, it can then roam to another.
WAN protocols include retry mechanisms that resend messages not
acknowledged from the subscriber device. These protocols can correct
problems from intermittent noise sources by retrying during a time slot
that does not coincide with noise source interference.
At a certain point, desensitising a wireless modem receiver creates
unacceptable coverage in the network. This usually is in the 10dB
range, though it can vary with networks.
The integrator should consult the technical staff at their target network
for any minimum RF desense performance levels and related
measurement methods that may be required for the device to be
accepted for customer use on that network.
Antenna
The Boomer II OEM modem is not equipped with an on-board antenna
and one must be provided externally in the host/terminal.
and one must be provided externally in the host/terminal.
Field Strengths from the Antenna
Field strengths from the wireless modem transmitter can reach as high
as 100 V/M for WAN products. Harden the host/terminal to withstand
these levels. LCD displays and switching power supplies are
particularly susceptible to RF. Capacitive decoupling of sensitive areas
is required. Decouple the reference voltage points on power supplies,
reset lines on processors, and keyboard scanning circuitry.
Field strengths from the wireless modem transmitter can reach as high
as 100 V/M for WAN products. Harden the host/terminal to withstand
these levels. LCD displays and switching power supplies are
particularly susceptible to RF. Capacitive decoupling of sensitive areas
is required. Decouple the reference voltage points on power supplies,
reset lines on processors, and keyboard scanning circuitry.
Antenna Interactions
There are two interactions that can impact the performance of the
antenna. The user, by placing a hand near the antenna can detune the
antenna and absorb energy. Accordingly, the antenna must be
positioned such that interaction between the user and the card is
minimized.
The host/terminal might also interact with the antenna. This is
particularly true for WAN modems, which have higher output power.
An imaginary sphere of real estate should be provided for the antenna
to function. Cabling for other peripherals must not interfere with this
region.
There are two interactions that can impact the performance of the
antenna. The user, by placing a hand near the antenna can detune the
antenna and absorb energy. Accordingly, the antenna must be
positioned such that interaction between the user and the card is
minimized.
The host/terminal might also interact with the antenna. This is
particularly true for WAN modems, which have higher output power.
An imaginary sphere of real estate should be provided for the antenna
to function. Cabling for other peripherals must not interfere with this
region.
Desense Summary
Desense considerations fall into two categories when using a wireless
device and computer as a system:
device and computer as a system:
The impact of the host/terminal EMI on system performance