First off, thanks to Dan for the modified tubing cutter idea! I'm going to
do some experimenting with that! Just so I'm clear, you "groove" the
elements AFTER you assemble them as opposed to using the "groove" as a stop.
I spoke with a friend years ago about Cushcraft antennas (they rank up there
with Microsoft for me) and their design. Specifically, the "boom effect"
you get from the elements making an electrical contact with the boom. I was
TAUGHT (yes, I can be taught as my wife would say) that "shorted-to-boom" or
"through-the-boom" designs are basically the same other than the physical
length change of the elements due to the "boom effect".
One problem with the Cushcraft design is that over the years the
"element-to-boom" clamp would loosen and allow the aluminum to
oxidize...thus insulating the element from the boom...thus changing the
electrical length of that element...and the performance of that antenna
would degrade.
His (WB9COY) suggestion was to WELD the elements to the boom to eliminate
any chance of the element becoming insulated due to oxidation (or buy his
superior design based on tests done by K1FO). So, you can take a horrible
antenna like a Cushcraft and make it perform as designed for years to come.
We were having problems with our 6-meter Cushcraft Ringo on a repeater here
in Southern CA. Armed with the preceding knowledge, I had a friend who owns
a local weld shop weld every element together and once tuned, weld the
tuning stub to the ring. To this date, the Ringo has performed as designed
(not saying that is good or bad). This antenna will not need to be broken
down. When it comes down, it will be thrown in the trash.
Welding a large antenna is not practical. Welding long elements in 10'
sections IS practical and will eliminate possible failure points. BUT,
before I did that, I would read "Physical Design of Yagi Antennas" by Dr.
David B. Leeson, W6QHS and strengthen those joints as they are never coming
apart again! The rest of the elements could be pop-riveted for future
dis-assembly.
As you can tell, I'm not a big Cushcraft fan...but, you get what you pay
for! I know that a tri-band Cushcraft works better than my G5RV. This is
not to say that the Cushcraft antenna can't be modified to be a real
performer as Leeson's book teaches. I know the there were modifications to
the old 11 element 2-meter beam that made it perform better than out of the
factory by using LESS elements...but that's another story.
I've welded antennas and it has worked GREAT for me! Make sure your welder
KNOWS how to weld aluminum!!! Also, if he is worth his salt, he will TIG
weld you antenna! Wire feed is not a good idea! Weld on those TOP MOUNTED
clamps (that should be bottom mounted) and KNOW they will never
move/slip/oxidize/etc!
Dino...K6RIX
----- Original Message -----
> After having a major project at work that involved a large amount of
> aluminum welding by our fabricator, I started to wonder why I had never
> heard of hams using aluminum welding to _more securely_ fabricate large
> booms and elements (eg. 80m and 40 m full size elements for yagis and
> verticals).
>
> Other than the obvious problem when deconstruction is desired, are there
> any other downsides to welding telescoping aluminum elements?
>
> 73, Scott W3TX
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