[TowerTalk] Rotating Dipole
abowen at nettally.com
Thu Jan 6 09:26:52 EST 2005
At 08:49 AM 1/6/2005 -0500, you wrote:
>I am in the process of putting up a full size rotating dipole for 40 meters..
>I plan to later shorten it to a loaded 40 foot dipole...the ultimate goal is
>to contruct a 2 element beam on 40...I need a source of loading coil core
>forms that are about one inch diameter. Also trying to decide if loading
>the elements or center loading the driven element woud be more efficient..
>any ideas...Dick W4NTG
I have been through the same thought and design process. I have concluded
that Cushcraft's short 40 design is hard to beat. You can scale the
dimensions from their web site. Exact dimensions are not critical.
You can buy fibreglas tubing from Allen Bond, WB4GNT at www.mgs4u.com
I have found that the program MOBILE, which has been included in the ARRL
Antenna Book software for several years, is quite accurate for designing
the elements. As an experiment, I made a half element and used it as a
vertical. I used 1" PVC (1.310 OD) for the coil form. You can use any
dimensions that are convenient, as long as it fits program parameters.
I do not advocate using PVC for the coil form. I used it because it was on
hand and I only intended to run low power to the experimental element.
When I put it up, it was a little off on the HF side, so I just lengthened
the tip and it was right on at 7030. I am currently using it as a backup
antenna over 30 radials. It is very useful when something appears off the
sides of the beam.
To make a rotary element, I just need another element half and a way to
support the 2 halves and mount it on the mast. I will probably use an old
Mosley driven element assembly that has 2 insulators per side. Bond also
sells some heavy wall tubing that may be useful as the center insulator.
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