MicrowaveradiorelaylinkZENITH80
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4.2 CONTROLCALCULATION
Thefollowingrelationshipisvalidforthecalculationofalevelattheoutputofthereceivingantenna,
i.e.,attheinputofthemicrowavereceiver:
P
in
[dBm]=P
vys
[dBm]+G
antV
[dB]+G
antP
[dB]–A
0
[dB]
where:
P
vys
[dBm] isthetransmittedoutputoftheoppositestation
G
antV
[dB] isthetransmittingantennagain
G
antV
[dB] isthereceivingantennagain
A
0
[dB] isthefreeenvironmentattenuation
The following relationship is valid for the attenuation of free environment during good climatic
conditions(withoutrainandfog):
A
0
[dB]=92.44+20log(d[km]∗f[GHz])
where:
d[km] distancebetweenantennas
f[GHz] usedfrequency.
The calculated values P
in
can be comp ared with the values measured by using the RSSI calibration
graph,orbydirectreadingofthevaluesgivenbythemonitoringprogram.
Ifthe constructedconnection has a partiallydisturbed firstFresnel zone thenthe attenuation due to
thedisturbancecannotbehigherthan‐6dBin
comparisonwithafreepath.Theopticalvisibilityalongthe
antenna axis hasto be maintained in anycase. In theopposite case retranslationwould have tobe used,
andthecriticalspotwouldhavetobecircumvented.
The additional attenuation of the path given by the disturbance of the 1st
Fresnel zone by a single
terrain obstacle with a sharp peak is represented by the graph (figure 28). The graph shows the relative
heightoftheobstaclezrelatedtotheellipsoid radiusofthe1stFresnelzone.Thevaluez=0representsthe
edgethattouchestheoptical
connection,i.e.,coveringof50%oftheellipsoidofthe1stFresnelzone.
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