MT-MR PLATINUM. POINT TO POINT AURAL RADIO RELAY SYSTEM
8
( 1)
α
= K + 20 log
10
f + 20 log
10
d [dB]
Where:
α
= Free Space Attenuation in dB.
f = System frequency in MHz.
d = Straight-line distance between Transmitter & Receiver, in Km.
K = Attenuation Coefficient:
K = 37.83 for Region I.
K = 32.58 for Region II.
K = 33.03 for Region III.
NOTE : Values of K are average values, and can suffer local appreciable variations
depending on the atmospheric conditions of a particular climate.
In order to illustrate the calculations performed, we can apply this and the following expressions to an
hypotetical link of any frequency band, say of the 2 GHz band. Assuming two points distant 32 Km., located at
Radio Propagation Region II. Suppose that assigned frequency is 2038 MHz (Channel V of 1.9 to 2.3 GHz Band). If we
substitute values in Expression (1) , we have:
If f = 2038 MHz
d = 40 Km
K = 32.58
Hence:
α
= 32.58 + 20 log (2038) + 20 log(40)
Solving:
α
= 130.9 dB
It's very interesting to arrive to a conclussive judgement with respect to Expression (1) :
"
Free Space Attenuation between two points increases logarithmically with the frequency used and with the
distance between the two points considered
".
1.3.- Path Profile Analysis.
In order to analyze Terrain's profile along propagation path, in first place we must obtain the Topographic Charts at
1:50,000 covering the whole intermediate region between the two considered points. If it's required, two or more
charts would be joined together at its ends, using transparent tape, to assemble the complete terrain's profile in the
region of interest.
Once Topographic Chart is assembled, it will be covered with a transparent sheet in order to preserve that maps
are not marked. Now we trace a straight line joining Transmitter and Receiver points, and using a rule marked in
Km in the same scale of the Charts used, we mark
the distance between the two points in one kilometer
(or mile)
intervals,
obtaining the true straight-line distance between the two points, as shown in the Fig. # 1 below :
