In a message dated 11/28/2006 8:02:22 P.M. US Mountain Standard Time,
vr2bg@harts.org.hk writes:
If this is an older SteppIR & therefore came with
the original tubes, something to remember...
Apparently the dielectric constant of later tubes
is different than previous ones.
Mixing old & new tubes is something I am not sure
how to accommodate with the controller. If only
change one tube for a new one, guess it is best that
it is used on the driver, as can easily find/fudge how
far to extend the strips.
Likewise a whole element - better to put the new
tubes on the driver than a parasitic element.
What to do if >1 element has new tubes & the
rest are old, I dunno.
My dipole has broken the element housing
instead of the tubes with winds not to different
than reported above. Not sure which I would
prefer to sacrifice. ;^)
73, VR2BrettGraham
Brett raises the needed concerns about mixing element vintage. In my case
here, my 3 element SteppIR (erected March 2003 by TowerTalk moderator K7LXC)
survived a 71 mph wind in July 2003 but a 80+mph wind in August 2006 broke a
driven element half. That necessitated replacement of the "older style"
element
support tube with the newer style.
The 3 el SteppIR here is mounted about 8 feet above a 3 element 40m yagi.
That puts it out of reach for me to do the replacement, even standing on the
40m antenna boom. My good friend KC7V, who is quite a bit taller than I am,
was
kind enough to do the repair. He could reach it ok, but put a temporary step
on the mast to make it easier. He replaced the half driven element tube only.
This mix of element vintage did shift the low swr points up in frequency
slightly, but certainly not enough to get excited about. A simple driven
element
length tweak brought things back into play nicely.
I did not notice any performance problems during either mode of CQ WW this
season. F/B remains excellent as before and I was pleased, as usual, with how
it played in the contests, since I take that aspect of our hobby quite
seriously.
I will eventually rebuild the entire antenna using the newer tubes. They are
stronger. That will probably happen sometime next year and be done with a
crane with man basket. It will be an easy one man job and I wont have to
dismantle the 3 el 40 yagi to get to it. At that time, I will changeout the
firmware to keep everything constant.
73,
Bob K8IA
Arizona USA
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|