Hi all...
I had a 15m failure on my C31XR. It's not the usual initial challenges
many have experienced, as this antenna was working correctly on all bands
when originally installed years ago. Nothing has changed with nearby
antennas and installation, and the SWR curves look fine on 10m and 20m -
just not seeing anything looking like resonance on 15m (no dips at all
between 15-27 MHz).
For those not familiar with the older C31XR, this is in the single
feedline, "open sleeve" feed arrangement. The balun (current choke)
connects at the 10m driver feedpoint, a close-spaced parallel wire
transmission line extends a couple feet to the 20m driver feedpoint, and
there is a matching coil across the 20m driver feedpoint. The 15m meter
driver is a few inches away from the 20m driver, but there is no direct
electrical connection to the 10m & 20m drivers. The 15m driver is shorted
at its feedpoint by a short jumper.
Visually, the elements all look fine, and I don't see anything wrong with
the center jumper on the 15m driver nor the feed system / matching
coil. The 10m and 20m SWR curves are fine, which also implies that the
10m-20m feed system is not the problem.
Maybe the center jumper is open on the 15m driver (looks OK from the ground
and seems unlikely). If the jumper is open, I'm not sure how that would
affect the behavior, so I can't test that hypothesis from the ground
(anyone know?).
Another possibility is that a nested/riveted joint between tubing sections
on the 15m driver isn't making contact, but that feels unlikely. Has
anyone ever had that problem before with a yagi (especially with riveted
elements)? Wouldn't a problem with the 15m driver also throw off the 20m
SWR?
To test DC continuity, I'll have to drop the antenna (15m driver isn't
reachable from the tower). Of course, once on the ground, RF performance
can't easily be checked, so if things check out at DC I'll still be lost.
Any other ideas/thoughts before I suck it up and put it on the ground to
test?
--Bill N7VM
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|