On Tue, Feb 17, 2009 at 7:41 PM, Richards <jruing@ameritech.net> wrote:
> I am not sure what you mean by this... as the Cushcraft MA-160V is only
> 30 to 36 feet tall (adjustable stinger) and only has a 40 kHz bandwidth
> on 160 meters. The 43 footer is taller, and can be worked anywhere in
> the band with a big outboard tuner.
With miserable efficiency! The MA-160V could easily be substantially
better, given the coax and balun losses inherent in the 43 foot vertical
approach, even though, as you point out, the MA-160V is shorter. But top
loading is a good thing for getting radiation resistance. I don't really
feel like modeling the radiation resistance of a 43 footer vs. a top loaded
36 footer... but it might be that the 36 footer wins.
W0MU says: "I wish there were some short miracle antennas for 80 and 160 so
I could put
up some 4 squares easily."
The suggested MA-160V or 43 foot antenna wouldn't be much of an array
antenna if what you're interested in is transmitting gain.
There's not much point in worrying about trying to build a transmitting
array until you're at least within a dB of the maximum gain you could get
out of a single element. If you follow Cushcraft's advice and use 8 radials
under your MA-160V or if you use a 43 foot vertical on 160m with no loading,
you're going to be a relatively huge amount down from 0dBi gain on your
antenna.
You can try to phase them for more gain, but the mutual coupling will tend
to drive the already low radiation resistances down. So you'd do a bunch of
work phasing them for getting the eqivalent of putting down more ground
radials, loading your 43 footer to resonance with a top hat, or any number
of other much easier approaches.
What's the point of phasing four -10dBi installations to end up at -7dBi
when you could just improve your single antenna to near 0dBi?
If you've got the land you need for a 160m transmitting array, you must also
have enough land to put down 60 120 foot radials and put up a 90 foot top
loaded irrigation tubing vertical or something, and you can focus your array
fiddling on being able to hear.
I might be wrong, and I'm sure our resident array experts will let me know
if I am, but I doubt there's much point to building a 160m transmitting
array with anything shorter than, say, 70 or 80 foot top loaded antennas.
You need each antenna to have nearly maximum gain on its own to bother with
the phasing for transmitting purposes.
73
Dan
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