428f812d   
   From: lumpy@digitalcartography.com   
      
   miso@sushi.com wrote:   
   > Do you mean the tower being like an AM radio type radiator? You need   
   > to isolate the tower from the ground with ceramic insulators...   
      
   Not really. You can shunt feed a grounded tower.   
   It's exactly the same principle as a Jpole antenna   
   or a gamma match on a yagi. Feed the grounded   
   element a given distance from the ground point   
   and you create the desired 50 ohms impedance.   
      
   > Anyway,   
   > there is usually a transmitter shack nearby.   
      
   That's what I wondered about the heft and size   
   of the tower. The transmitter guts could be   
   located inside the tower. With extremly high   
   frequencies, there is no "feedline". The output   
   of the transmitter finals is connected directly   
   to the horn or whatever is doing the radiating.   
   Radar and even the 1200MHz hams do that.   
      
   I suppose it's possible that the internal structure   
   of the thing is more traditionally "tower shaped",   
   that is larger at the base, tapering to the top.   
   And the outside is a fascia. But again, it seems   
   kind of weird to involve all the secrecy just for   
   some kind of antenna tower.   
      
   In terms of engineering tower buildings, is there a   
   point where the thing can be the same size at the   
   base as it is at the top? There are multi story   
   buildings that certainly exist in that manner.   
   They probably aren't as tall as our tower, but   
   they are several stories high and the same size   
   at the base as they are at the top. There are,   
   of course, some that are built opposite. ATC   
   towers, those "golf ball on a T" looking water   
   towers, some dedicated "crows nest" style   
   observation towers are built on a straight "pole".   
      
      
   Craig 'Lumpy' Lemke   
      
   www.n0eq.com   
      
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