[Moon] [Moon-Net] Help With H-Frame & Elevation

Chuck Smallhouse w7cs at theriver.com
Sun Feb 8 18:47:21 CET 2015


Hi Gedes,

My strong recommendations based on many years of experience.

Only utilize square aluminum tubing throughout your "H" frame 
assembly.  It's the only way to assure long term proper yagi 
alignment, especially those that are as long as 5 W/L.  the cross 
boom should be 3-5" square and with 3/16" - 1/4" thick walls.   Even 
so there should be guy wires supporting it in two planes.  The 
vertical risers that support the yagis can be 2" square tubing with 
1/8" walls.   Square U bolts are commonly available in hardware stores.

For vertical/elevation motion using a linear actuator, I've 
successfully used large barn door hinges attached to the thick 
mounting plates that are attached to the square cross  boom and to 
the rotator mast, which can be 2" round tempered  steel  (not 
SS).  The cross boom should be mounted on this mast as close to the 
top of the tower as possible,

One end of the linear actuator can now be mounted to the round 
vertical tube, a ways above the cross boom, and the other end 
attached to the cross boom.  It would 'pull up' the array in this 
configuration.

A very satisfactory elevation indicator system can be made from the 
internals of a digital level, or a weighted pendulum arm, either 
geared to, or directly attached to a Helipot, whose readings are feed 
into a very stable W7IUV bridge circuit, with a digital panel meter 
display.  It is also very handy, and a psychological, benefit, to 
have a very small and inexpensive video camera co-mounted on the 
cross boom.   Its video output can be displayed, in the shack, on one 
of those automobile video screens (~7"), that are used for back seat 
DVD viewing.

BTW, by sightly lengthening the boom, you could now drill it and add 
additional elements and a feed, to make it into a "cross polarized" 
system,  If the yagis are mounted in a "X" (vs +) 
manner/configuration, the booms would not be required to be 
insulated.  The phasing lines could now be dressed along the yagi 
booms and down the vertical risers and along the cross boom to the 
power dividers.  This would result in much less phasing line loss and 
a better mechanical support for them.

You now have the option of selecting H or V polarization in RX and 
TX, or maybe better, TX in both polarizations simultaneously.

GL es 73,

Chuck,  W7CS



At 06:48 PM 2/7/2015, Gedas wrote:
>Hello group.  I am currently working on a 4-yagi 2m EME array using 
>5 wavelength antennas.  I would rather not use a heavy-duty rotor 
>where a center boom runs thru the rotor.  I am required to keep 
>costs to a minimum and I like the idea of using a linear actuator to 
>tilt the array up and down.
>
>I was wondering if someone could share with me some proven designs 
>or ideas or point me to some online resources to help me design and 
>construct the required H-frame and tilting mechanism for such an array?
>
>
>Gedas, W8BYA EN70
>
>Gallery at <http://w8bya.com>http://w8bya.com
>Light travels faster than sound....
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>
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