I played with it a bit and found that converting it to a T from an L
actually reduced the overall gain at 30 deg elevation and did not improve it
below that. I ended up with 73' on each side of the center for the T,
slightly inverted. In fact, I took the inverted L in one of my files
(already constructed) and just added the 2nd wire. I, did, of course shorten
the vertical section to the 42' that I have available.

It did eliminate the overhead radiation, but did not significantly improve
the low angle (which seems impossible), but I'll play some more. So far, it
looks like the Inverted L is the better choice, even for more power at lower
launch angles than the "T". (It is also easier to construct...for a quick
throw it up antenna, you only need a long piece of wire and an insulator at
the top, pullling as much wire as you can get to go vertical and stretching
out the rest.) Then, the real work comes, putting down a good radial field
before the frost.

Thanks for the tip. 73

....hasan, N0AN
"Roy Lewallen" wrote in message
...
hasan schiers wrote:
Now that is interesting, Roy. I was going to put up a 160 m inverted L
this summer. I am limited to only being able to go up about 45 feet, so I
would need about another 90 feet horizontal.

Are you suggesting that it might be a better arrangement to go up the 45'
and then put up the top "T"?

It might be. You might benefit from the radiation from the horizontal
portion of an L, and you might not. But if it's quite low, the radiation
will be mostly straight up, and a fair amount will be expended warming up
the ground. Neither will occur with a T.

If so, roughly how long should the top part of the T be (each side of
center) to get me to 160?

That's just what antenna modeling programs are for! Dust off your EZNEC
and you'll have the answer in minutes.

. . .

Roy Lewallen, W7EL

I found the error, I had to fix two conditions that I had changed in the
model:

Copper wire (for loss)
Ground characteristics

Now that both antennas have the same conditions, the T has ever so slightly
better gain at 20 degrees than the Inverted L. Not enough to bother with the
increased complexity, and the input Z is now down around 5 ohms for the T
and 8 ohms for the L.

Now, is it worth matching the 8 ohms up to 50 at the feedpoint, or just
using the tuner in the shack to take care of it? (coax feed, LMR-400, about
50')

....hasan, N0AN

"Roy Lewallen" wrote in message
...
John Ferrell wrote:
. . .
I am a perpetual antenna student!

And so are we all.

Roy Lewallen, W7EL

Since you are talking about 50 Ohms I assume you are talking about a
transmission line. If that is the case you should definitely match the feedline
to antenna at the antenna feed point. Any attempt to match the feedline with a
tuner in the shack only turns the whole feedline into part of the antenna
system. By doing that you have lost any good work in building the antenna.

Dan

hasan schiers wrote:
I found the error, I had to fix two conditions that I had changed in the
model:

Copper wire (for loss)
Ground characteristics

Now that both antennas have the same conditions, the T has ever so slightly
better gain at 20 degrees than the Inverted L. Not enough to bother with the
increased complexity, and the input Z is now down around 5 ohms for the T
and 8 ohms for the L.

Now, is it worth matching the 8 ohms up to 50 at the feedpoint, or just
using the tuner in the shack to take care of it? (coax feed, LMR-400, about
50')

...hasan, N0AN

"Roy Lewallen" wrote in message
...

John Ferrell wrote:

. . .
I am a perpetual antenna student!

And so are we all.

Roy Lewallen, W7EL

dansawyeror wrote:
Since you are talking about 50 Ohms I assume you are talking about a
transmission line. If that is the case you should definitely match the
feedline to antenna at the antenna feed point.

Why is it definite? What is the loss in 50 ft. of LMR-400 at the
frequency of interest when the SWR is 50/8 = 6.25:1?

Any attempt to match the
feedline with a tuner in the shack only turns the whole feedline into
part of the antenna system.

Simply not true if the currents remain differentially balanced.
SWR doesn't cause feedline radiation.
--
73, Cecil http://www.qsl.net/w5dxp


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On Sat, 27 Aug 2005 15:26:25 -0500, "hasan schiers"
wrote:

I found the error, I had to fix two conditions that I had changed in the
model:

Copper wire (for loss)
Ground characteristics

Now that both antennas have the same conditions, the T has ever so slightly
better gain at 20 degrees than the Inverted L. Not enough to bother with the
increased complexity, and the input Z is now down around 5 ohms for the T
and 8 ohms for the L.

Now, is it worth matching the 8 ohms up to 50 at the feedpoint, or just
using the tuner in the shack to take care of it? (coax feed, LMR-400, about
50')

If you would go he

http://www.qsl.net/ac6la/tldetails.html

download the program and enter your load Z and 50' of LMR400 @ 3.5
MHz, you would immediately see the answer to your question.

If the 8 ohm is real (j=0) then the total loss is all of 0.4 dB and if
the line is 50' long, the resulting input Z is easily matched with low
loss.

On Sat, 27 Aug 2005 14:31:06 -0700, dansawyeror
wrote:

Since you are talking about 50 Ohms I assume you are talking about a
transmission line. If that is the case you should definitely match the feedline
to antenna at the antenna feed point. Any attempt to match the feedline with a
tuner in the shack only turns the whole feedline into part of the antenna
system. By doing that you have lost any good work in building the antenna.

The feedline is -always- part of the antenna system. If it troubles
you to think about matching in the shack, just think of the
transmission line as part of a matching network located at the
feedpoint. In other words, the feedpoint network is comprised of 50'
of coax and coupla LCs in a box. This network then connects to the
transmitter through a non-resonant (flat) coax line.

Let's take the case of a 50 Ohm line and some mismatched antenna. The result is
a combination other then 50 Ohm with most likely a zero complex component. All a
tuner does is match 50 Ohm at the radio to the complex impedance presented to it
at the source of the line.

That the only place with 50 Ohms and zero inductance in the line - antenna
system. The combination of cable and antenna presents something other then R =
50 ohms 0 reactance and the the transmission line see discontinuities. The
result is it radiates.

Dan

Cecil Moore wrote:
dansawyeror wrote:

Since you are talking about 50 Ohms I assume you are talking about a
transmission line. If that is the case you should definitely match the
feedline to antenna at the antenna feed point.


Why is it definite? What is the loss in 50 ft. of LMR-400 at the
frequency of interest when the SWR is 50/8 = 6.25:1?

Any attempt to match the feedline with a tuner in the shack only turns
the whole feedline into part of the antenna system.


Simply not true if the currents remain differentially balanced.
SWR doesn't cause feedline radiation.

I am not sure what you mean by -always-. If you mean there is no such thing as a
perfect coax line then your statement is true but does not add any real value.
If you mean by -always- the feedline is a significant component in the antenna
system then I would have to disagree. When operated at their design point coax
transmission lines do not radiate and are not part of the radiating "antenna
system".

Coax is designed to work in a specific environment as a transmission line. These
transmission lines are designed not to radiate. When transmission lines are
operated significantly outside their design range the radiate. Adding a tuner to
one end only controls the characteristics at that point. It does not 'clean up'
the mismatchs.

Dan



Wes Stewart wrote:
On Sat, 27 Aug 2005 14:31:06 -0700, dansawyeror
wrote:


Since you are talking about 50 Ohms I assume you are talking about a
transmission line. If that is the case you should definitely match the feedline
to antenna at the antenna feed point. Any attempt to match the feedline with a
tuner in the shack only turns the whole feedline into part of the antenna
system. By doing that you have lost any good work in building the antenna.


The feedline is -always- part of the antenna system. If it troubles
you to think about matching in the shack, just think of the
transmission line as part of a matching network located at the
feedpoint. In other words, the feedpoint network is comprised of 50'
of coax and coupla LCs in a box. This network then connects to the
transmitter through a non-resonant (flat) coax line.

Cecil Moore wrote:


Why is it definite? What is the loss in 50 ft. of LMR-400 at the
frequency of interest when the SWR is 50/8 = 6.25:1?


Ok, I need teaching here. Why would the loss change? The loss on the
line is forced to what happens at the nominal 50 ohms doesn't it? The
SWR shouldn't be able to change it unless the voltage limits are hit I
would think. I need an explanation of why it wouldn't be so.

Thanks.

tom
K0TAR

On Sat, 27 Aug 2005 17:49:42 -0700, dansawyeror
wrote:

I am not sure what you mean by -always-. If you mean there is no such thing as a
perfect coax line then your statement is true but does not add any real value.
If you mean by -always- the feedline is a significant component in the antenna
system then I would have to disagree. When operated at their design point coax
transmission lines do not radiate and are not part of the radiating "antenna
system".

An antenna tuner or transmatch, if you prefer, doesn't radiate and is
part of an antenna system. the fact that a transmission line radiates
or not doesn't mean it isn't part of the system.

Danny, K6MHE