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Satellite amplifiers, to rack mount or hub mount them?

In the design of a teleport or even a VSAT terminal, one of the important decisions is whether to mount the amplifier safely in an air conditioned control room, or place the amplifier on, or very close, to the antenna in the open air.

The outdoor mount, is most commonly called a hub mount option. The disadvantage to this method is that the amplifier must be made to withstand, heat, rain, snow or dust storms and still continue to function for many years. The additional armor plus more rugged components adds to the cost of the amplifier.

To offset the higher purchase price, the feed to the amplifier (which is most commonly a BUC) is L-Band, and the L-Band IF signal can be carried over long distances with very little loss using a cheap cable. Because the amplifier is mounted only a few feet from the antenna feed, there is very little loss of the RF power traveling such a short distance.

The disadvantage of hub mount BUCs is that the seldom come in the higher power range required by many teleports, the high power is normally provided by tube based amplifiers called TWTAs and most TWTAs require the environment that can on be provided by an air conditioned operations center.

There is another difficulty to using indoor or rack mount amplifiers, their output is RF and connecting this high frequency to the antenna can be expensive. The two most common methods of the amplifier to the antenna is by a rigid rectangle of metal called waveguide. The per foot cost of the waveguide is high and a complete support structure must be manufactured to hold the waveguide firmly in place.

In the case of large teleports they will often build an outdoor shelter as close to the antenna as possible, so that the waveguide run is minimized.

There are loss calculations to be made, because whenever RF frequencies are carried from point to point there is always signal loss in each foot of the cable or waveguide.

To summarize there is no clear answer to rack mount or hub mount question, each case must be taken on its own merits, and the best decision arrived at.

Redundant antenna mountingImage of redundant Terrasat amplifiers
Rack Mount Amplifierimage of MT5000 Amplifier