Sam (et al),
When it was by itself my XM240 I measured the forward and reflected power using
two different Drake W-4 wattmeters. The SWR in the first two columns below was
caculated by the formula (Pf+Pr/Pf-Pr). The third column was obtained by using
a Mirage SWR meter in the shack. The Drake measurements were at the end of 85'
of new coax but similar readings were measured in the shack through another
100' or so of coax. While I don't believe the actual readings from the Drake
meters, their relative readings seem to show there is little effect on my XM240
by the TH6. The TH6 boom is parallel to the XM240 boom and the TH6 is 10'
below the XM240. I split the CW and LOW measurements on the XM240.
On the other hand, when installed under the XM240, the TH6's minimum SWR point
on 15 meters (I haven't measured resonance yet) moved downward about 200 KHz
from where it was when the TH6 was pointed straight up with the reflector about
20' above the ground. The behavior on 20 and 10 meters was not noticeably
effected. The TH6 was tuned for LO PHONE.
Freq SWR (solo) SWR (w/TH6) SWR (w/TH6 and Mirage SWR meter)
7.0 1.17 1.12 1.3
7.1 1.00 1.04 1.1
7.2 1.06 1.04 1.2
7.3 1.30 1.17 1.6
Based on my results, I don't think I will rotate my TH6 90 degress unless the
TH6 15 meter performance is poor. I have not had time to try the TH6 yet
because I have been busy becoming a grandfather.
73, Brian WA5UEK
____________________________ Reply Separator _________________________________
Subject: [TowerTalk] XM240 interaction - question
Author: Sam Ferris <ve5sf@sk.sympatico.ca> at !SMTP/INTERNET
To: <towertalk@contesting.com>
Date: 10/17/98 10:48 PM
Wonder if any CC 402cd or XM240 owners can give me some advice regarding
interaction associated with a XM240 and a TH7 stacked about 6 feet apart
(that's all the space I reasonably have). Here's the situation.
Put up my new XM240 a couple of days ago - 5.25 hours on the tower
removing the old Hygain 402 BA and pulling and assembling the XM240 up
through a couple of other antennas. The TH7 is mounted at 70 feet just
above the top of the tower and the XM240 is about 6 feet above that. The
booms are perpendicular to each other since that is the way that I had
the hygain 402 mounted previously to reduce SWR impacts on 15 metres on
the TH7. Presently the SWR on the XM240 is a little high, bottoming
out at about 1.55 at 7.050 , 1.8 at 7.000 and 2.0 at 7.125. I set it for
the CW setting in the manual and followed the advice regarding the
measurement mistakes in the manual posted by others - most helpful. In
comparison to the Hygain 402, it seems that impacts on the TH7 are about
the same, the 15 metre SWR curve looks about the same as before and the
SWR on 10 and 20 metres is now actually lower than with the previous 40
metre antenna.
My question is if any others have similar setups with PARALLEL BOOMS, and
if such a change to my system would reduce the impact on the XM240 by
lowering the SWR. Bottom line is I am not all that anxious to make many
more trips up the tower to spin it.
In a continuing note on the new CC product, it certainly seems like a
strudy antenna. The alignment on the predrilled holes on mine were all
fine except for maybe one on the boom which was relatively close. Had to
trim the heat shrink as posted by others. Mine was missing one of the
small right angle mounting plates on the balun, (the one at the coax end
of the balun) so I neded up using a hose clamp to secure one end of teh
balum to the boom. Other than that I am pleased with the structural and
assembly aspects of the antenna.
Any experiences or advice would certainly be appreciated.
... Sam
VE5SF
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