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Q2. Which specifications for the tower must be specified by tower buyer/ Communication system designer ?

Ans 2. The buyer must decide/specify the following parameters, before asking for an offer from tower supplier. All the following factors will affect the cost of the tower.
a) Height : Height of tower must be determined by “Line of sight survey”. Normally money spent in survey is more than compensated by savings in tower cost and resulting reliable communications. If height of tower is less than required height, then communication will not take place. If height of tower is more then required height, then signals will overshoot the desired area and create interference and other complications.
While deciding the height of tower, availability of clearspace around tower site should be kept in mind.There should not be any hazardous installation e.g electric pole . inhabited building within falling distance of tower.
If tower is being installed on a roof top then structural strength of building will be controlling factor.
Cost of a tower varies approximately as square of its height.
b) Expected loading on tower – Amount of load on tower will determine whether it is light weight, standard or heavy duty etc. Normally the factors, which constitute major portion of load are
i) Survival wind speed - Doubling the survival wind speed will increase the forces acting on tower 4 times. The metrological data of any area provides the maximum wind speed, which has occurred in that area during last 10 years or 50 years .
ii) No of antennas – their physical sizes, weights, levels on tower and firing angles.
iii)Spare structural capacity for additional loading of antennas in future.
iv) Appurtenances required on tower i.e.
a) Platforms, with /without railing, internal/external, levels on tower.
b) Climbing ladder with safety loops, monkey ladder / staircase.
c) Cable ladder – width required to accommodate required number of cables.
d) Safety climbing devices – e.g Fall Arrestor , if required any.

c) Twist and Sway permitted – when wind blows, the antennas mounted on tower are going to twist and sway. The communication system designer will permit only for a limited amount of twist and sway. Beyond this level of twist and sway, the communications will be lost. Lesser twist and sway will require the tower to be more rigid, therefore tower will be more expensive.
d) Any constraint on geometry of towers – Broad casting towers will require a specified length of tower to be of specified width only. A specified length of top portion is normally required to be parallel to mount the antennas with vertical space diversity. Space available on ground may be constrained due to nearby buildings or installations. This constraint will require the base of the tower to be less than the space available. Buyer may be interested only in 3 legged or in 4 legged tower. This should be specified to get desired offer. The top width of the tower, if required to be of a particular value, it should also be specified.
e) Soil Report - If foundation cost is to be clubbed with tower structure cost to establish a total minimum cost solution, then soil's safe bearing capacity and level of water table should be provided. A regular soil investigation report will be helpful.