[TowerTalk] Force 12 C31XR Modeling

[john at kk9a.com]

I have used a C31XR at a station in the Caribbean and seem to recall higher
SWR on 15m. I'm not sure if that is a common issue.

I have a C3S that I brought to WP2AA. Only the 20m element was fed, the rest
of the elements were parasitically connected. With the C31XR, is Romax used
to connect the driven elements?

John KK9A


[TowerTalk] Force 12 C31XR Modeling
David Needham aa4vt wrote:
Hello Towertalkers,

I have built an EZNEC model of the Force 12 C31XR utilizing a single coax
feedline for a friend that is rebuilding a used one. I have a pretty good
model working with EZNEC Pro2+ v 7.0 and AutoEZ, but I had to make an
assumption for the 14/2 Romex with the ground wire removed that is used for
a transmission line from the 10m to 20m Driven Element.

I found that someone had posted a MINNINEC model back in 2010 or so, but
they used separate feedlines and didn't use the transmission line. I came
up with that the impedance of the transmission line must be about 120 ohms
to get the approximate curves with the stock dimensions. Has anyone else
done this and has a better number?

He is experiencing high SWR on 15m, minimum of 1.86 at 21.126 MHz. It would
require drilling out rivets, but I am finding that the spacing between the
15m and 20m element may need to be adjusted, at least according to the
model. Has anyone had this issue and corrected it?

In the JK Antennas version of the C31XR, I see they have changed over to
aluminum angle iron. Has anyone retrofitted a Force 12 C31XR with angle
iron or square tubing replacing the Romex transmission line?

Any help would be greatly appreciated. He is trying to get us ready for CQ
WPX Phone contest at the end of March.

-- 
Thank you!
David Needham, AA4VT (formerly K4AJA and K8AJA)