Well, as most of you know, I had a bunch of questions regarding the
construction of my new Cushcraft XM-240, 2 element 40M beam.
Unfortunately, my e-mails to Cushcraft's technical support, the
Cushcraft President, and another Cushcraft employee resulted in
ZERO replies.
Thanks to Fred, KG9X, my co-worker, who is also simultaneously building
a new XM-240 for helping me dig further on these issues. He had
a tech support guy try to answer some of our questions. Unfortunately,
the tech support guy called Fred's home number during the day, thus
avoiding further question or clarifications of his answers.
Here is what we have found so far, and any comments from Cushcraft.
1) The three boom sections join with a smaller diameter insert with
four through bolts per joint. If we were lucky, we were able to line
up two of the four (through) holes and the remaining two holes had to
be re-drilled to allow the bolt to pass through. Of course if the
existing holes were nearby, it's quite a sloppy fit. Cushcraft needs
to drill these holes more precisely.
2) No where in the manual do the suggest, recommend, or require the
use of Nolax, Penotrox, or any other anti-corrosion material, nor do
they include any with the antenna. Cushcraft needs to, at a minimum,
recommend the use of such. Cushcraft should include some with the
antenna.
3) There was an error in the manual about one of the element section
lengths. The manual says 41" for section EB. Due to the double walling
of this section, it can only be inserted so that a minimum of 45" is
exposed. I figured this must have been a typo and continued building
with 45". Cushcraft said that 45" is correct.
4) The manual states that the half length of the element, up to the
LCA (loading coil assembly) should be 160". Adding up the lengths of
the sections of the reflector results in 160". Adding up the lengths
of the driven element, plus the 1" from center of the center insulator,
results in 161". I assumed that Cushcraft would have wanted the LCA
at the same physical position so I shortened on of the sections (ED)
1" such that the length was restored to 160". Cushcraft tech support
says that the 160" should be the length of the aluminum only, not
including the length of the center insulator, contrary to the manual
picture. This means that the LCA is one inch further from the boom
than the reflector LCA. Cushcraft needs to correct the manual.
5) The manual says the exposed length of the LCA should be 18.5".
All 8 of our LCA's could not be inserted enough due to the heat
shrink tubing preventing it from doing so. Fred and I assumed the
length was correct and carefully trimmed the shrink tubing to allow
us to do so. Cushcraft tech support says you should trim the heat
shrink tubing. Cushcraft needs to correct the length of the heat
shrink tubing in production to allow the section to be inserted 18.5".
6) The manual lists element half lengths for CW/MID/PH. They do not
include their interpretation of where exactly that means. Is CW 7.000
or 7.050? etc. They also do not include graphs (as they do with their
other products) of SWR versus frequency versus element length settings.
Therefore, we cannot interpolate were we wish to personally tune the
antenna. Cushcraft tech support claims that the SWR graphs are
"proprietary" and cannot publish them although their 1998 catalog
includes SWR graphs for their R7000, R6000, A4S, A3S and A3WS antennas.
The manual for the X9 40M add-on lists center frequencies. The
Cushcraft tech support guy did tell Fred that the frequencies were
7.025, 7.125 and 7.225 MHz for CW/MID/PH, respectfully. Cushcraft
needs to add this in their manual.
7) Aside from assembly issues, the manual states 28dB (maximum) front-
to-back. Is this measured? I'd love to see that data that supports
that. Of all the computer modeling I (and others) have done, 28 dB is
a good figure for a 3-element yagi. 12dB is much more realistic for a
2 element design.
If you have one of these antennas on order, are thinking about buying
one, or already have one on the way, keep this message as a addendum
to the manual. You'll need it.
Good luck!
---
Chad Kurszewski, WE9V e-mail: WE9V@qth.com
The Official "Sultans of Shwing" Web Site: http://www.QTH.com/sos
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