Dan etal,
I haven't been following this thread closely so pardon me if I repeat
something. This note is specifically aimed at 160 meters.
The 43 foot vertical is probably OK on 160 if you have a good radials
system and a low loss tuner right at the base of the vertical.
I have used the Cushcraft MAV-160 and tested it pretty thoroughly. My
first one I gave to PJ5NA and if any of you are 160 people, you'll
know the Jim has a reasonable signal on 160 without high power.
The MAV-160 as per the Cushcraft instruction manual is not very
efficient but does work. Using their recommended radial system using
only 400 feet of wire does in fact give a reasonable VSWR leading one
to think all is OK but it's not efficient.
I had an 80 meter radial system that I use for tests comprised of
about 30 65 foot radials. I mounted my first MAV-160 over it and the
VSWR was pretty poor. I think the measured impedance was about 20
Ohms. The improved radial system lowered the losses. However it
worked fine albeit a high VSWR. Next I placed a shunt inductor across
the feed of about 7 microhenries wound on a PVC tube, slightly
readjusted the top whip for resonance at about 1.820 MHz and voila,
1:1 VSWR with a reasonable bandwidth. My bet is that 30 radials about
30 feet long would still do fine.
How did it work? I worked lots of DX with it. Many stations gave me
comparisons. The worst report was 4 dB below my 70 foot top loaded
tower with 32 foot 1/4 WL radials. Most of the time there was only a
slight drop below my normal antenna and on several occasions I worked
through Pacific DX pileups without realizing I had the MAV-160 on
line instead of the tower!
Now it's not necessarily the recommended best 160 meter DX antenna
but for those of modest means or small lots and 25-30 foot radials as
long as possible, it's surely a good bet to get you on the band and
be able to work DX. The price is now higher than when they were
first announced but still not a bad deal.
73,
Joe, W1JR
At 09:04 PM 2/17/2009, Dan Zimmerman N3OX wrote:
>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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