Afar Logo
Home arrow Support arrow RF Link Budget Calculator

RF Link Budget Calculator

This 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 Wireless Ethernet Bridges, 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.



You need to enable Java in your computer to run the RF Link Budget Calculator

 

Microwave Link Budget Analysis - Parameters

Overview

The 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 loss

This 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 each of our pulsAR radio models to operate a four different RF speeds.  Lower speeds give you a better sensitivity.  The table below shows you the sensitivity values of each model when operating it at its maximum speed.  Refer to the pulsAR data sheet for the sensitivity values at all the speeds supported:

Model:
AR-9010E
AR-9027E
AR-24010E
AR-24027E
AR-24110E
Maximum Speed (Mbps):
1.1
2.75
1.1
2.75
11.0
Rx Sensitivity (dBm):
-95
-92
-92
-90
-86

 

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 Loss

Free 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.
 
AFAR Communications, Inc | 81 David Love Place | Santa Barbara, CA | USA 93117
T: +1 805 681-1993 | F: +1 805 681-1994