At 04:12 12/2/98 , Scott Neader KA9FOX wrote:
>I have a small city lot with a single 72 foot self supporting tower. I
>would like to get on 160m mainly for domestic contests, but also to play
>with some DXing.
================================>
Scott,
Here is what I did, and I copy the reflector in, just in case others
might find it interesting.
My tower is 65' of Rohn 45.
I got some aluminum tent poles and hose clamped them to the tower
struts so that they projected out as far as possible from the tower. In
the swedged down part of the tent pole that would normally go into the
tent grommet I screwed in insulators (the type with the large lag
screws in the base). They screwed in almost perfectly, just as though
they had been designed together.
Through the insulators, I ran my inverted L wire.
I started at about 10' up the tower.
I bonded the braid to the tower via connecting it to the tent pole.
I ran the wire up the tower as high as I could go and ran the balance
of the wire down at an angle to a tree in the front yard.
In order to get a proper match of 1:1 SWR (down from the 2:1 that the
antenna wound up with) I used some door knob capacitors across the feed
point until I reached a nice match.
I am in the process of adding an RF choke to the feed point (ON4UN
ferrite bead type) just because I want to do so. To date, I have found
no need for same. But, what the Hell, this is ham radio, and I'm a ham.
I also am in the process of putting a vacuum variable capacitor in a
box and putting it at the feed point so that I can tune the electrical
length of the wire to resonate all over the 160 meter band. Similar to
what was recently shown in recent CQ Magazine. Your described capacitor
should work quite well.
BTW,
My antenna plays really quite well, but KZ5MM thinks that a large
contributing factor to my antenna doing so well is the fact that my
tower (and hence my inverted L ground) is all bonded to my swimming
pool grid which is about 4 feet away from my tower. The swimming
reinforcement grid, it is surmised, makes a very nice ground for my
system.
Thinking that you might not have a pool up in North 9-Land , you might
gain some overall improvement by running a single elevated radial. If
no room for a full size radial, then load it with a coil so as to make
the radial an equivalent 1/4 wave. Feed the L antenna via making your
braid connection to only the elevated radial as ON4UN described once
upon a time in an earlier writeup that he did.
The only problem I have now is that the L wire runs up the side of the
tower and creates a logistics problem when I try to turn my second
tri-bander mounted down at the 32' level. Eventually, as you might
understand, the second tri-bander driven element comes up against the L
wire. I am going to run the L wire in a bit at that point so as to
place it closer to the tower and allow for the tri-bander to turn. It
will be interesting to see what happens to the performance when this is
done.
My single tower installation is very heavily loaded, and allows me to
operate all bands. It can be seen on a section of my home page.
If you take your picture, and cram a pool in the back yard, we wind up
with about the same situation; right down to the position of our trees.
Your antenna will do very well in domestic contests, and you will be
surprised at how much DX you will also get.
My next step is to figure out what type of low noise antenna to use
with the new bandpass filter and pre-amp I just got for the band. Looks
like you have room for ewes which is more than I can claim for myself.
Do it.
It will work fine for you.
Use your capacitor, and use your green wire.
73,
N5RP
--
FAQ on WWW: http://www.contesting.com/towertalkfaq.html
Submissions: towertalk@contesting.com
Administrative requests: towertalk-REQUEST@contesting.com
Problems: owner-towertalk@contesting.com
Search: http://www.contesting.com/km9p/search.htm
|