[TowerTalk] Rotator loops

[Joe Subich, W4TV]

> I assume that most of those turns, as Jim suggests, are for 
> nesting and extending the telescoping mast on the TV truck. 

The commercially available nycoils are on the order of 36 inches 
in diameter when not extended.  

> 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.

If one assumes three turns with 8" diameter at maximum clockwise 
rotation and a clockwise coil, rotating 360 degrees counterclockwise 
will result in two turns with a 12" diameter.  Starting with three 
turns, 8" diameter in a clockwise coil and the antennas at the 
counterclockwise stop, rotating 360 degrees clockwise will result 
in four turns 6" diameter.

One of the problems with commercial nycoil sections is that the 
sizes are limited.  If I recall correctly, the largest tubing 
was 1.25" which limited the capacity to two .405" cables and 
a couple smaller control cables.  It was very difficult to "pull" 
an 80' nycoil (used with the 56' masts) with 2 x .405 cables. 

73, 

   ... Joe, W4TV 
  



> -----Original Message-----
> From: towertalk-bounces at contesting.com 
> [mailto:towertalk-bounces at contesting.com] On Behalf Of Pete Smith
> Sent: Saturday, February 27, 2010 11:31 AM
> To: jimlux
> Cc: Tower and HF antenna construction topics.
> Subject: Re: [TowerTalk] Rotator loops
> 
> 
> 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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