Hi all,
Several of you asked for the results of my survey concerning a triangle of
MA160V's (160m vertical from Cushcraft), and the idea of elevating the base to
stay clear of our six foot snow base. Thanks to all of you who took the time to
respond, I appreciate it very much. Here are some interesting points:
1. Everyone agrees that snow is a good insulator. Many hams don't worry about
snow around the base of a ground-mounted vertical. New one on me!
K1FK in Maine pointed out:
Actual measurements with a GenRad 1606B show negligible changes in feedpoint
Z from summer to worst
of winter (yet to come here in N. Maine). Each element of the 40M array has
120 1/2-wavelength
radials beneath it and the big vertical in the middle has 120 1/4-wave (on
160M) radials, and both
systems are well bonded together.
All of my Beverages have been buried beneath snow for last several months ...
no impact whatsoever
on performance.
Another note:
No need to worry about the snow. I have a 4-square for 40 and a 80 meter
vertical ground mounted and during the winter months snow is 4 ft deep over the
bases, has no effect on the performance of the verticals in any way. Snow
apparently is a great insulator, the SWR remains the same regardless of snow
covering the bases or not. Friend of mine is using the MA160V on 160 and lives
in a snow area and has never mentioned any problem.
73 Gary K7OX
One more:
Paul, I have a number of verticals for 160m -> 40m that have the base
covered in deep snow during the winter, and I see no problems at all. I
would not go through the trouble of trying to elevate the base 7' because
of snow.
73 de Peter SM2CEW
2. Many thought it was a good idea that if I was going to raise the mount up
seven feet that there should be a choke at ground level. I think that's a good
idea also.
3. The real "deal-killer" for me was this thought:
Note that the antenna is about 32 feet tall or 1/16 wavelength (wl). It is
center loaded which means the radiating part is 1/32 wl (below the loading
coil). That is equivalent to a mobile antenna on 40 meters, 8 feet tall or 4
feet tall on 20 meters.
In my humble opinion the radiating efficiency is equivalent to 16% of a 1/4
wl vertical or 25% of a normal inverted-L, assuming a reasonable ground
system.
Also please note that Cushcraft has only a few radials so the antenna
matches 50 ohm coax. Most of the 50 ohm antenna impedance is ground loss
further reducting the efficiency to less than 5% of a 1/4 wl vertical.
An inverted-L antenna hung off a tower with a decent radial system is a much
much better choice, as is shunt feeding a tower with a radial system.
YMMV - GL es 73, George K8GG
My conclusion:
Forget the Cushcraft antenna(s)!! Put up one or more 1/4 wave verticals or an
inverted-L, however you need do it.
If I'm going to spend that kind of $$$$ on the phasing network, it might as
well be for decent metal in the air. (I'm a firm believer that more metal =
better antenna:>) I think in my case that another tower is in order, or maybe I
can use a 50' tree I see out there as support for the inverted L. Back to the
ON4UN manual for more head-scratching.
Again, thanks to all who responded. CU on the TB!
73,
Paul
WY7I
San Juan Mtns, of So. CO. (P.S. It's snowing again.)
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