Distance Distance Bandwidth
Ant1
Gain
Ant2
Gain
RF
cables Freq FRSPL
RF
power ERP
Rx
Thrshld
Link
Mrgn
in miles
in km
in kb/s
in
dBi
in
dBi
in dB
in
GHz
in dB
in
dBm
in
dBm
in dBm
in
dB
24.3 39.1 512
31.0
31.0
6.6
5.80 140 20 51 -91 22.5
1.6 2.6 256
14.0
14.0
4.0
2.45 108 20 34 -94 25.2
Table 1: Fade Margin Chart
You can also calculate your own path loss using the integrated radio link margin
calculator included on the Carlson Wireless product CD in a folder called “Calculators”.
This is an approximate calculation – an exact calculation includes factors such as local
weather patterns and must be performed by a qualified engineer.
What’s an acceptable fade margin? The rule of thumb theory is that 10 dB of fade
margin will deliver about 90% reliability and 20 dB will deliver over 99% reliability.
Because there is only a small ground wave component involved in the radio propagation,
the above numbers presume a clear first Fresnel Zone. A fade margin of 20 dB is
suggested to overcome multi-path degradation and polarization. On long paths (over 20
miles) particularly at 4.9 GHz and 5.8 GHz, it is better to have 30 dB of fade margin.
2.1.6 Interference
The 2.4 and 5.8 GHz radio bands are unlicensed and shared. All users in the band must
accept all other signals within the band, interfering or not. Devices operating in this band
can become a source of interference for Trailblazer products. If the interfering signal is
stationary and has a bandwidth less than 3 MHz, it will not create any significant problem
even if it is 100 times (20dB) stronger than the receive threshold. If the interfering signal
has a bandwidth wider than 4 MHz and is 10 times (10dB) stronger than the receive
threshold, it can render channel(s) unusable. If the interfering signal is frequency
hopping throughout the band, such as the LAN bridge device, and is only 1/10 (–10dB)
as strong as the receive threshold, it can cause significant dropouts.
Some examples of these devices are:
Video Transmitters
Video transmitters use analog radios which are usually fixed in frequency, utilize 6 to 10
MHz of bandwidth and are low power with an ERP of less then +10dBm.
Cordless Phones
Cordless phones are narrow band and fixed in frequency (during each use), utilize 1 to 2
MHz of bandwidth, are low power with an ERP of less than +10dBm. It is strongly
recommended to avoid the use of 2.4GHz cordless phones in the vicinity of Trailblazer
products.
Local Area Network (LAN) Bridges
Wireless LAN devices are true spread spectrum devices. They either frequency hop, a 1
MHz bandwidth over the complete band, or utilize CDMA of 16 MHz bandwidth and are
stationary. ERPs can range up to +30dBm.
Trailblazer Installation and User Manual
7
