I've played a bit with inverted Ls, but I'm going to try one on a 100
foot tower with a TH5 at 100 feet, 28'8" 6-meter yagi at 115 feet and
the UHF and VHF arrays at 130 feet.

By my calculations the tower should be close to a half wave, or
slightly shorter than a half wave.

I know that some tower heights and antennas can pose a problem such as
the 70 feet and a tribander listed in the handbook.

This antenna will be about 80 to 90 feet vertical and the rest
horizontal.

Has any one out there tried anything close to this?

Roger Halstead (K8RI EN73 & ARRL Life Member)
www.rogerhalstead.com
N833R World's oldest Debonair? (S# CD-2)

Roger,
Have you thought about just shunt feeding the tower?
'Doc

Roger Halstead wrote in message . ..
I've played a bit with inverted Ls, but I'm going to try one on a 100
foot tower with a TH5 at 100 feet, 28'8" 6-meter yagi at 115 feet and
the UHF and VHF arrays at 130 feet.

By my calculations the tower should be close to a half wave, or
slightly shorter than a half wave.

I know that some tower heights and antennas can pose a problem such as
the 70 feet and a tribander listed in the handbook.

This antenna will be about 80 to 90 feet vertical and the rest
horizontal.

Has any one out there tried anything close to this?

Roger Halstead (K8RI EN73 & ARRL Life Member)
www.rogerhalstead.com
N833R World's oldest Debonair? (S# CD-2)

Dunno...Offhand, I don't think it will look that long myself. The
largest beam is 30 ft lower than the top. I think that will reduce the
effectiveness as a hat. The beams on top are fairly small per 160m,
and probably won't amount to a whole lot. Unless indicated otherwise
by an analyser, I'd assume it to act just a tad longer than a 1/4
wave. You could add top loading wires if you wanted to raise the
current max higher up the tower. Being the tower is likely grounded,
I'd shunt feed it. You could also probably rig up a linear loaded
sloper also.
But a top hat with even symmetrical spokes would give you a cleaner
vertical pattern, with an overhead null. If you run a wire to only
80-90 ft, and then out horizontal, I don't think the height of the
tower will matter. It won't be part of the antenna, except maybe for
close coupling. Or do you mean running the wire out from the grounded
tower itself? MK

On Sun, 28 Sep 2003 13:39:41 -0500, 'Doc wrote:



Roger,
Have you thought about just shunt feeding the tower?

Mater'a'fact...that's my other option. The problem with shunt feeding
the tower is all the wire antennas hanging from it. Two half wave,
center fed 75 meter slopers and one half wave center fed sloper for
40. That and the tower is only 10 feet from the corner of the
attached garage.

I have some concerns about a 160 vertical and all that house wiring
right next to it. It does have a good ground system with over 500
feet of #2 bare copper just under the surface and 25 8' ground rods
cad welded to it. That's good electrical and safety ground though and
a bit shy for a good ground under a vertical.

However IF I can make the shut feed work then I don't have to find a
support for the end of the inverted L.

Roger Halstead (K8RI EN73 & ARRL Life Member)
www.rogerhalstead.com
N833R World's oldest Debonair? (S# CD-2)

'Doc

(Mark Keith) wrote in message . com...
Roger Halstead wrote in message


But a top hat with even symmetrical spokes would give you a cleaner
vertical pattern, with an overhead null.

Was just thinking...if you had the antenna a 1/2 wave in electrical
length, with long top hat wires, they could radiate a good degree, and
you might not have an overhead null. Still would probably work pretty
well overall though. Ground losses would be less than a 1/4 wave. You
could model that to check. MK

Roger,
I wish I had that kinda problem (LOL). I think I'd
have to give the shunt feeding a try. All the antennas
hanging on the tower should act as capacitive hats (might
try with them both shorted and not shorted, see what the
difference is). As for the house wiring, who knows till
you try it? The part that would stop me would be the trips
up the tower...
'Doc

PS - Former owner of the second most costly Ercoupe in
the world, N415E. Don't ask.

Roger:

Somewhere I believe I read that you have a good ground plane under the
tower, but consider an alternative: I have a 100' tower which has numerous
VHF antennas and a couple of HF dipoles hanging off of it. Tip elevation is
130' AGL. I added 4 elevated radials at 10' and brought all the feedlines
out below that level. I am sure that the dipoles must add some capacitance
loading, but with a gamma match and tuner at the antenna, I get 170 kHz
usable bandwidth (SWR2:1) on 160 meters without retuning.

--
Crazy George
Remove NO and SPAM from return address
"Roger Halstead" wrote in message
...
I've played a bit with inverted Ls, but I'm going to try one on a 100
foot tower with a TH5 at 100 feet, 28'8" 6-meter yagi at 115 feet and
the UHF and VHF arrays at 130 feet.

By my calculations the tower should be close to a half wave, or
slightly shorter than a half wave.

I know that some tower heights and antennas can pose a problem such as
the 70 feet and a tribander listed in the handbook.

This antenna will be about 80 to 90 feet vertical and the rest
horizontal.

Has any one out there tried anything close to this?

Roger Halstead (K8RI EN73 & ARRL Life Member)
www.rogerhalstead.com
N833R World's oldest Debonair? (S# CD-2)

On Mon, 29 Sep 2003 11:33:30 -0500, "Crazy George"
wrote:

Roger:

Somewhere I believe I read that you have a good ground plane under the
tower, but consider an alternative: I have a 100' tower which has numerous
VHF antennas and a couple of HF dipoles hanging off of it. Tip elevation is
130' AGL. I added 4 elevated radials at 10' and brought all the feedlines
out below that level. I am sure that the dipoles must add some capacitance
loading, but with a gamma match and tuner at the antenna, I get 170 kHz
usable bandwidth (SWR2:1) on 160 meters without retuning.

Glad to hear that...My feed lines all come out underground through
conduit and make a good 75 to 80 foot run to the basement wall.

My only concern has been the radiation getting in to the house wiring.
Well, besides matching that is.:-))

Elevated radials are pretty much not an option, due to the shop,
driveways, and flower beds. I'm going to go ahead and play around
with shunt feeding, starting at roughly 70 to 80 feet and maybe a 24
inch spacing, then working from there.

Roger Halstead (K8RI EN73 & ARRL Life Member)
www.rogerhalstead.com
N833R World's oldest Debonair? (S# CD-2)

Roger:

I think you are trying to make a simple task difficult. Think about why you
can't just hook a feeder to the base of the tower. Actually, you can,
except matching it is a bitch because of the verrrry low impedance. So, go
up a few feet (I use 20', as it is a common tubing length), and make it a
gamma, delta, or whatever is convenient. Then use a "tuner" to match
whatever appears to 50 ohms. Mine is a few microhenries of series
inductance, with a few hundred picofarads of shunt capacitance at the 50 ohm
end. I actually use a fixed inductance and a series capacitor instead of a
variable inductor, but that is a construction detail.

--
Crazy George
Remove NO and SPAM from return address

On Wed, 1 Oct 2003 15:11:29 -0500, "Crazy George"
wrote:

Roger:

I think you are trying to make a simple task difficult. Think about why you
can't just hook a feeder to the base of the tower. Actually, you can,
except matching it is a bitch because of the verrrry low impedance. So, go
up a few feet (I use 20', as it is a common tubing length), and make it a
gamma, delta, or whatever is convenient. Then use a "tuner" to match

That's kinda, sorta, something like I'm thinking of doing. Other than
at 160 meters the tap will probably be some where around 70 feet with
a spacing of (SWAG here) of 18 to 24 inches. Then a series matching
cap, just like in a gamma match,

Then check with noise bridge and adjust accordingly.

whatever appears to 50 ohms. Mine is a few microhenries of series
inductance, with a few hundred picofarads of shunt capacitance at the 50 ohm

I'd like to get it set so I don't need any series inductance, just a
little capacitance.

I'm currently trying to finish up a rebuild on the old Henry 2K4 in
the shop, repaint the cabinet on an HT-33 that has a great front panel
and nice chassis, and unfortunately I'm waiting for the wind to let up
so I can let the top mast down to check the antenna hardware as well
as replacing the pigtails. (That means about 6 to 7 hours on the
tower). Oh..I forgot the HyGain AV640 that is ready to go on top of
the 32 foot tower at the end of the shop. (which naturally has a big
tree limb in the way which is too high to reach even with a big
extension ladder)

Roger Halstead (K8RI EN73 & ARRL Life Member)
www.rogerhalstead.com
N833R World's oldest Debonair? (S# CD-2)

end. I actually use a fixed inductance and a series capacitor instead of a
variable inductor, but that is a construction detail.