Hi Guys
I have been reading the mail on this subject and would like to offer my
recent experience:
1) The new Cushcraft XM240 does indeed differ slightly from its forerunner -
the 402CD.
It has an insulated reflector element and the 402CD's reflector was at DC
ground potential. According to the design manager for the XM240 antenna,
this modification was made to give the XM240 a cleaner pattern. The two
elements remained at nearly the same lengths as the older 402CD and general
performance characteristics (such as minimum SWR and SWR bandwidth) were
predicted to be similar.
2) I have stacked the XM240 above a new Cushcraft X9 tribander on the same
mast at a distance of **8**feet - in the same plane. Thus the XM240 is at
123 feet and the X9 is at 115 feet. I should note that I did **not** use a
commercial balun nor a coaxial choke of 10 turns at the XM240 feedpoint.
Rather, I made up my own "sleeve" balun to feed the XM240 which consisted of
5 ferrite cores, each about 1" long with a hole in the middle such that they
could be accomodate RG213 passing down the center. These are round and can
be purchased from Amidon or Palomar I think. I purchased mine from KM1H at
Radiokit - but Carl's firm is no longer in business under that name.
The 5 ferrite cores are tightly bunched together, one after the other,
right at the pigtails of the Rg213 feeder - and taped together. To keep
these things (and they are heavy) from fracturing in a wind against the Xm240
boom, I then put the whole mess INSIDE an 18" piece of washing machine drain
hose. The hose just slipped over the ferrite cores - and I then taped up
each end of the hose liberally to seal out water seepage. Finally, the drain
hose was then taped to the side of the boom in several places to prevent
movement. I should note that the 402CD at 66 feet is fed in exactly the same
manner. The X9 is fed with RG213 through the standard Cushcraft balun
(200/50 ohms) that is provided with the X9 by Cushcraft.
The 40M SWR curve is really quite remarkable as follows:
7000 1.3/1
7050 1.1/1
7100 1.4/1
7150 1.6/1
7200 1.8/1
7250 2.2/1
7300 2.4/1
The X9 produces a **typical** X9 SWR curve - as follows:
14000 1.9/1 - dropping to 1.5/1 at 14040 - dropping to 1.3/1 at 14100 and
remaining there up through 14350
21000 1.3/1 dropping to 1.2/1 by 21000 and remaining below 1.4/1 through 21450
28000 1.4/1 dropping to 1.3/1 by 28100 - and staying below 1.5/1 through
28700.
It drops again (due to a dual 10M driven element) above 29.0 - but I never
have used it above 28700. (No need).
I have been using this antenna combination for almost 2 years now with
seemingly excellent results - in DX and contests. 40M is mated with a 402CD
at 66 feet and the X9 is now triple stacked with two lower X9's at 78 and 39
feet. The lower X9's (when fed alone) yield the **same** identical SWR curve
as the upper one - even on 15M.
>From what I have been told and from what I have read, it seems as if the new
XM240 produces differing impacts depending upon what kind of tribander it is
mated with.
For example, K3OO has his XM240 at 18 feet above a new Force 12 C31XR on the
same mast. Initially these two antennas were in the same plane and Rick's
15M performance was a **dog**! Rick then offset the 40 by ninety degrees on
the mast and it cleared his problem nicely. This is not always a cureall for
40/15M interaction as others have noted - but it did cure HIS problem.
It is a royal pain in the rear to have to do this - but it was his only
solution. Rick also had a high SWR problem on 15M with his C31XR. 15M was
resonating LOW and 20M was resonating HIGH. The remedy was to cut 3" from
either side of the 15M C31XR driven element which RAISED the 15M resonant
point while LOWERING the 20M resonant point. I am told that others have
experienced this problem with the new C31XR antenna.
As often happens, the real world results when stacking a 40M yagi and a
tribander on the same mast can be very different. The older TH6 combined
very well at about 10 feet spacing with a 402CD. Usually the 40M yagi was
placed at the top of the mast if I recall.
I have been more than pleasantly surprised with my XM240 above my X9
tribander - in the same plane at a distance of 8 feet. Actually, the real
distance is about 7.5feet and the two antennas have worked beyond my
expectations.
I thought I would pass this along to others - as one combination that
**WORKS** in the "real world" - which is the only one which matters to us
amateurs and Dx'ers.
73 JEFF
K1ZM@aol.com
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