----- Original Message -----
From: "Jim Lux" <email@example.com>
To: "Chuck" <firstname.lastname@example.org>; "Merlin-7 KI4ILB" <email@example.com>;
"AA6DX - Mark" <firstname.lastname@example.org>; "Mike Rhodes" <email@example.com>;
Sent: Tuesday, September 19, 2006 10:28 AM
Subject: Re: [TowerTalk] Tower mast..
> At 07:22 AM 9/19/2006, Chuck wrote:
>>Grab the kids old bicycles or any off a junk heap to cannibalize the
>>pedal sprockets. Have the machine shop mill out the center of one
>>sprocket to fit around the mast at window level. Weld the sprocket
>>to the mast. Drill two holes in the window base to allow the chain
>>to run through the window.
>>Take the second bike and cut the sprocket hub off with sections of
>>the bike frame still attached so you can use hose tie down clamps to
>>mount to a flat surface next to the desk. Attach chain and manually
>>rotate the antenna.
> Chain drives aren't so hot for bidirectional loads. You need some
> slack in the chain to account for mechanical movement, stretch, etc.
A dynamic tensioner (spring loaded) is relatively easy to build, but yes
that does add to the complexity of the system and can get down right hairy
for longer chains. You can use a groved spindel or a small sprocket that is
spring loaded. Actually you *might* be able to use the tensioner they use at
the rear wheel. Use an old derailer for support.
The problem with cables or chains is that slack. They need to be relatively
tight BUT a remote actuated brake at the mast might make them doable. The
brake could be a simple flange with a series of holes and a spring loaded
bolt operated by a rope. So what is it has 5 to 10 degree resolution.
Rotate the antenna to peak the signal release the brake and them move the
antenna slightly until the bolt drops in a hole.
Unlike the complicated antenna array that kept getting simpler, when you
start with a simple system it can only get more complicated.<:-))
Roger Halstead (K8RI and ARRL 40 year Life Member)
N833R - World's oldest Debonair CD-2
www.rogerhalstead.com (Use return address from home page)
> so you wind up with backlash in the system. You can put a tensioning
> system in, but that adds a level of complexity. Chain drives also
> have trouble when the chain is running sidewise (if it goes slack, it
> tends to fall off the sprocket, just like a derailleur on a bike).
> But chains work well in other applications, good idea...
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