Where does the power go?
 

Take a dipole, cut for 3.922. Put it up as an inverted V
with the apex at 30' and the ends at 10'. Feedline is 100'
of 450 ohm ladder line/12t 5-1/4" coax balun/30' rg58.

Antenna works nice, esp at night.

Now take the same setup and feed it with an L network
autotuner, say an LDG AT100 pro and run it on 1.825
mhz. Feeding the antenna as a marconi is not an option
due to lack of ground area for radials.

Where does my 100w go? is it lost as heat in the tuner?
(my guess) Is it lost in the feedline due to high SWR at
the apex?

73'd de Ken KG0WX

Where does my 100w go? is it lost as heat in the tuner?
(my guess) Is it lost in the feedline due to high SWR at
the apex?


No; the tuner has fairly good QF components: there is a reason your tuner has
no huge fans or heat sinks.

Some lost as heat in coax from mismatch insertion loss. Much lost from ground
losses; some power now goes straight up rather than at lower elevations.

73,
Chip N1IR

"Ken Bessler" wrote in message
...
Take a dipole, cut for 3.922. Put it up as an inverted V
with the apex at 30' and the ends at 10'. Feedline is 100'
of 450 ohm ladder line/12t 5-1/4" coax balun/30' rg58.

Antenna works nice, esp at night.

Now take the same setup and feed it with an L network
autotuner, say an LDG AT100 pro and run it on 1.825
mhz. Feeding the antenna as a marconi is not an option
due to lack of ground area for radials.

Where does my 100w go? is it lost as heat in the tuner?
(my guess) Is it lost in the feedline due to high SWR at
the apex?

73'd de Ken KG0WX



Hi Ken:

On 1.824MHz, 4.5 db of your power (3db equals 1/2 of the power) is lost in
the feedline. I know that 450 ohm line is supposed to be so low loss that it
doesn't matter, but a 80m dipole on 160m presents such a very bad match that
even open wire line has loss. I would make your antenna as showing a load
of about 10J -1250Ohms. Don't feel bad if you were feeding this with coax
the excess loss due the miss-match would be over 20db. The 4.5db doesn't
include the loss in the coax balun, and the tuner. According to the ARRL
review of tuners on 160 with a SWR like that 25% of the power is lost in the
tuner. These numbers were derived from modeling the antenna with EZNEC and
the TL program that comes with the ARRL handbook. Other people with slightly
different models will get slightly different numbers but the bottom line is
a 80m dipole is a very bad antenna on 160m. You could be losing 1/4 of your
power in the tuner and well over 1/2 of what's left in the feed line. But if
its all you have the use it.


--
John Passaneau, W3JXP
Penn State University

On Thu, 14 Oct 2004 07:01:36 -0500, "Ken Bessler"
wrote:

|Take a dipole, cut for 3.922. Put it up as an inverted V
|with the apex at 30' and the ends at 10'. Feedline is 100'
|of 450 ohm ladder line/12t 5-1/4" coax balun/30' rg58.
|
|Antenna works nice, esp at night.
|
|Now take the same setup and feed it with an L network
|autotuner, say an LDG AT100 pro and run it on 1.825
|mhz. Feeding the antenna as a marconi is not an option
|due to lack of ground area for radials.
|
|Where does my 100w go? is it lost as heat in the tuner?
|(my guess) Is it lost in the feedline due to high SWR at
|the apex?

Using readily available tools, Multinec, XLZIZL.xls and TLDetails.exe,
all available at www.qsl.net/ac6la I computed the following.

Two wires, fed at the junction with a split source:

Wire 1 coordinates (ft):

End 1 End 2
X Y Z X Y Z
0.000 -55.285 10.000 0.000 0.000 33.000

Wire 2 coordinates:

0.000 0.000 33.000 0.000 55.285 10.000

Resonant at 3.922 over average ground. At 1.825 MHz the feedpoint Z =
12.53 -j 1366.

I copied these values to XLZIZL and defined a feed network that
(beginning at the antenna) consists of 100' of Wireman type 553, 35'
of RG-58A, a series capacitor = 1754 pF and a shunt inductor = 2.14
uH.

Now, I don't know whether the LDG tuner will configure itself this way
or not, but this is the optimum solution. The input Z of this mess =
49.19 +j 0.4. SWR = 1.02

XLZIZL gives the total network loss as: ~9.0 dB.

To see where the losses come from we can first look at the L network
and see that with the component Q's I used: Qc =500 Ql =200, the loss
is only 0.09 dB.

The best way to see the line losses is to go to TLDetails and first
select 100' of Wireman 553 and a load Z of 12.53 -j 1366.

The program shows that the total line loss is: 7.7 dB, most of it
attributable to SWR. The input impedance of this line section is 5.58
+j2.11.

If we use this value for the load Z and change the line to RG-58A with
length 35', we find that the loss is ~ 1.35 dB.

As a sanity check, we add the three losses 7.7 + 1.35 + .09 = 9.1 dB,
just as was determined earlier.

So most of the power is burned up in the "low loss" ladderline!