If you have such a structure IMHO the best thing you can do is to shunt
feed it. It is really easy to do. Just drop a three or four wire
"cage" down from the 60 foot level supported by two pieces of galvanized
water pipe extending each about 24-36 inches from the tower. ..... and
feed the wires at the bottom with a series capacitor or two capacitors
with an Omega match. You can then tap this wire down to the tower at two
foot increments. To prevent having to move a "sweet point" tap up and
down the tower it may be easier to measure the impedance and the
inductive reactance and make a network to match what you have. The
three or four drop wires should be at least 24 inches from the tower and
can avoid changes with wire sway by holding them tight with some nice
hardware store springs after you attach some good porcelain insulators.
In my case I use a flat wound AM BC coil to ground which is tapped from
the ground up and a series vacuum cap from the cage wire to the coil so
i can get a perfect match. This way I can use a single coil and a
single variable and by tapping the coil I can cover a wide range of
impedance. For a really great synopsis of information of shunt feed
methodology just visit W8JI.com and it is all there for you.
herb Schoenbohm, KV4FZ
On 12/18/2015 1:11 PM, Robert Harmon wrote:
Stan,
With shunt feed I would gain the 18 foot mast with the yagis, the
total overall height is 108 feet.
I haven't really considered shunt feeding. I see your point of the
wires with an L in proximity to other
antennas. That was a worry I had with the 40 meter yagi and the L. I
will look into shunt feeding. I have ON4UN's book, probably should
start there to bone up. Any other resources to learn abut shunt
feeding ?
The top band archives probably has a lot of discussions about shunt
feeding also.
thanks Stan,
Bob
K6UJ
On 12/18/15 1:36 AM, Stan Stockton wrote:
Bob,
There is no reason I can think of to not shunt feed the tower as it
is with either ground radials or elevated radials. An inverted L
isn't as good as a vertical for DX and you would just be adding
clutter and horizontal wires in proximity to your other antennas.
Shunt feeding a tower is very, very simple.
73... Stan, K5GO
On Dec 17, 2015, at 8:06 PM, Robert Harmon <k6uj@pacbell.net> wrote:
I am planning an install of a 160M inverted L and would like
critique from you top banders.
I was originally planning a separate tower for 160 but my XYL has
squashed the idea :-)
My tower is 90 feet fully extended with a 18 foot mast currently
used for a Force 12 WARC plus 10/15 beam
on top and a N6BT DXU-32, 2EL 40 and 3EL 20 12 feet below.
At the top of the top section I have a 10 foot fiberglass pole I
plan to extend out to support the vertical, so it will be 10 feet
away from the tower.
I am thinking of feeding the vertical and having 4 elevated radials
at the 14 foot level.
So the vertical wire will about 76 feet long.
I am wondering if I would be better lowering the feedpoint & radial
tie ins down from 14 feet say to 8 feet and have more length in the
vertical portion of the L or better to have the 14 feet elevation
for the radials ?
Also the horizontal leg of the L on top will be about 5 feet below
the 40/20 yagi only 10 feet out from the tower,
do you think this is OK as far as interaction between the yagi and
the 160 L ? Anything else I should consider ?
I have never had a decent 160 antenna, just hoping I can work
something out with my existing situation
thanks in advance,
Bob
K6UJ
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