RF Link Budget CalculatorThis radio link budget calculator tool lets you quickly compute the Free
Space Loss, Received Signal Strength, Fade Margin ,
Distance and more. You can use it for planning your RF links with our PulsAR-24027 Wireless Ethernet Bridge , or with other radios in any frequency band. It
includes a Coaxial Cable Loss Calculator with pre-loaded loss
parameters for a variety of LMR and Belden coaxial
cables.
The calculator is a Java applet which should work in your browser. If you are not familiar with all the terms used you can
read about the various parameters below the calculator. If you
have any comments or suggestions for improving this calculator send us a message.
Microwave Link Budget Analysis - Parameters
OverviewThe calculator tool assumes a generic RF link between
two sites. Site 1 is viewed as the transmitter and site 2 as the
receiver. At each site you have a radio connected to an antenna
through an RF cable. The calculator assumes you have "line of sight"
between the two antennas. You can use our Fresnel zone and antenna height calculator to help determine if that is the case.
For any set of input values the calculator always computes the Free Space Loss and the Signal Strength at the Receiver. Additionally you choose a third output between the link Distance, Fade Margin , or Transmit Power . This lets you quickly answer the most common questions when designing a radio link:
1. How far can my radio link go while maintaining an acceptable Fade Margin ?
2. What Fade Margin will I get for a radio link of a certain distance?
You can change all the input parameters with the up/down "spinner"
controls. As you change the input the calculator instantly updates
the output values. By seeing the results immediately you can quickly
evaluate trade-offs between different parameters.
Transmit Power
Transmit power at the radio RF connector specified in dBm. If your
radio specifies the transmit power in mW (milli-Watt) you can convert
to dBm using the equation:
Tx power in dBm = 10 * log (Tx power in mW)
Cable lossThis
parameter includes all the losses between the radio RF connector and
the antenna, which include the signal attenuation as it propagates
through the cable and losses in any connectors along the way. The
cable loss calculator at the bottom allows you to compute these losses
for specific cables. Use the drop down menu to select the cable type
or select "other" and enter the cable loss per 100 feet (or per meter)
at the frequency of operation. The calculator assumes an additional
loss of 0.25 dB for each connector in the cable.
Receiver Sensitivity
Minimum signal strength at the input of the radio at which point the
"Bit Error Rate (BER)" in the link is at a specified value. Most
manufacturers use a BER of 1x10-6 (1 bit error in one
million bits) to specify the radio receiver sensitivity. However make sure
you check the specifications when comparing the sensitivity in radios
from different manufacturers.
You can configure the PulsAR-24027 radio to operate a four different
RF speeds. Lower speeds give you a better sensitivity. Use the
appropriate value from the table below:
RF Speed
|
2.75 Mbps
|
1.375 Mbps
|
500 Kbps
|
250 Kbps
|
Rx Sensitivity:
|
-90 dBm
|
-93 dBm
|
-95 dBm
|
-98 dBm
|
Fade Margin
The Fade Margin is the difference between the Received Signal Strength and the radio Receiver Sensitivity
. When you deploy a link you want to have a Receive Signal Strength
that is sufficiently above the radio Receiver Sensitivity in order to
survive signal fading due to a variety of factors. These factors might
include slight misalignment of the antennas, losses due to fog and
rain, etc. As a rule of thumb you should try to get at least 15 dB of
fade margin in your links.
Free Space LossFree
Space Loss refers to the reduction of the signal strength as the signal
radiates away from its source. When there are no obstructions every
time you double the distance the signal is reduced by a factor of 4.
This is equivalent to subtracting 6 dB from your signal strength. The
Free Space Loss assumes no obstructions in the link path which is
sometimes referred to as having "line of sight". However, note that
"line of sight" means that at least "60% of the first Fresnel Zone " is clear of any obstructions. Refer to our Fresnel Zone Calculator page for more details.
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