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
The World Contest Station Database, updated daily at www.conteststations.com
The Reverse Beacon Network at http://reversebeacon.net, blog at
reversebeacon.blogspot.com
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)
>
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