[TowerTalk] Rotator loops

[Pete Smith]

I assume that most of those turns, as Jim suggests, are for nesting and 
extending the telescoping mast on the TV truck.  For a ham application, 
with a maximum of 450 degrees rotation between stops, it seems likely 
that a couple of 8-12" diameter turns would probably be enough.  In 
fact, I had such an arrangement for a few years, but then an antenna pro 
while doing some other feedline work re-rigged it in the traditional ham 
style. It was remembering that which prompted me to write.

73, Pete N4ZR

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On 2/27/2010 9:33 AM, jimlux wrote:
> Pete Smith wrote:
>> I notice that typical ham rotator loops involve an unsupported loop 
>> that is perpendicular to the mast, and attached at top and bottom.  
>> It seems to me that this means a lot of flexing through 360 degrees, 
>> and in the wind.  I have also noticed that TV station remote trucks 
>> seem to use another solution for their rotating dishes - they wrap a 
>> few turns of coax loosely around the mast, so that a one-turn 
>> rotation only slightly loosens or tightens the wrap.  Seems like this 
>> would be a better, more durable practice for ham installations too.
>>
> I agree.. they also do this to accommodate the big difference in 
> height as the mast extends, so the coax neatly stacks as it comes down.
>
> But, ZOMG,(<grin>) adding each loop of coax (if about 4 feet in 
> diameter) adds 10-12 feet of coax, and at $.50/ft, that's $5 per extra 
> wrap. And what about the loss? Each of those turns adds 0.05dB at 10 MHz
>
> (actually,all joking aside, if you were on 10m, the loss might be 
> something to contemplate.. an extra 10 turns would start to add up, 
> although antenna gain on 10m is pretty easy to come by.. making up the 
> dB of coax loss is probably not tough)
>