Hi. I've heard and read some about ladder line and dipoles.
So what is the basic configuration look like? My impression is
the set-up starts with either a balanced tuner with 400 ohm output
or a 50 ohm tuner with a 4:1 balun to the 440ohm ladder line. The
ladder line then runs to the dipole and that's pretty much about it.

So my EZNEC on my future backyard Vee shows about 60ohm which is about
a 12:1 mismatch at the antenna feedpoint! So do I have something wrong
in the basic config? Or do you all put a balanced impedance
transformer up at the antenna feedpoint?

Just a little confuzed?


jimg
Oregon
USA

jimg wrote:
Hi. I've heard and read some about ladder line and dipoles.
So what is the basic configuration look like? My impression is
the set-up starts with either a balanced tuner with 400 ohm output
or a 50 ohm tuner with a 4:1 balun to the 440ohm ladder line. The
ladder line then runs to the dipole and that's pretty much about it.

So my EZNEC on my future backyard Vee shows about 60ohm which is about
a 12:1 mismatch at the antenna feedpoint! So do I have something wrong
in the basic config? Or do you all put a balanced impedance
transformer up at the antenna feedpoint?

Here's what I did and it works very well.

http://www.qsl.net/w5dxp/notuner.htm

An SWR of 12:1 on ladder-line is acceptable but where did that value
come from? 440/60 is 7.3:1. And your 440 ohm ladder-line (Wireman #554)
is probably closer to 360 ohms.
--
73, Cecil

jimg wrote:

ok, got me. to be accurate, eznec says the feedpoint Z is
32-j68.5...the apex is only 60' in the sky so the feedpoint impedance
is not too high. so that's where the 12:1 roughly came from (i was
playng with the height above ground).

so the question remains, ppl really run a very high swr at the
feedpoint..is there any advantage to matching at both point? i.e.
a fixed balanced impedance transformer up there at the feedpoint, and
then, of course, a tuner down here.



jimg wrote:
Hi. I've heard and read some about ladder line and dipoles.
So what is the basic configuration look like? My impression is
the set-up starts with either a balanced tuner with 400 ohm output
or a 50 ohm tuner with a 4:1 balun to the 440ohm ladder line. The
ladder line then runs to the dipole and that's pretty much about it.

So my EZNEC on my future backyard Vee shows about 60ohm which is about
a 12:1 mismatch at the antenna feedpoint! So do I have something wrong
in the basic config? Or do you all put a balanced impedance
transformer up at the antenna feedpoint?

Here's what I did and it works very well.

http://www.qsl.net/w5dxp/notuner.htm

An SWR of 12:1 on ladder-line is acceptable but where did that value
come from? 440/60 is 7.3:1. And your 440 ohm ladder-line (Wireman #554)
is probably closer to 360 ohms.

jimg
Oregon
USA

On Tue, 17 Jan 2006 01:20:34 GMT, jimg wrote:

jimg wrote:

ok, got me. to be accurate, eznec says the feedpoint Z is
32-j68.5...the apex is only 60' in the sky so the feedpoint impedance
is not too high. so that's where the 12:1 roughly came from (i was
playng with the height above ground).

so the question remains, ppl really run a very high swr at the
feedpoint..is there any advantage to matching at both point? i.e.
a fixed balanced impedance transformer up there at the feedpoint, and
then, of course, a tuner down here.

Jim, you can explore the options yourself. My transmission line
calculator at http://www.vk1od.net/tl/tllce.php will allow you to
specify the load impedance from your NEC model or transformer, and
calculate the losses on Wireman 55x ladder line.

For example, if you used 80' of 551 ladder line on 3.6MHz and the
feedpoint was 32-j70, the loss would be 0.5dB and the Z at the tx end
of the line would be around 380-j1200.

Owen

PS: I am a little surprised how low the R of you modelled feedpoint
is... I would have expected round 60 ohms, give or take.
--

jimg wrote in
:

Hi. I've heard and read some about ladder line and dipoles.
So what is the basic configuration look like? My impression is
the set-up starts with either a balanced tuner with 400 ohm output
or a 50 ohm tuner with a 4:1 balun to the 440ohm ladder line. The
ladder line then runs to the dipole and that's pretty much about it.

Tuners with baluns in them are inferior to true balanced tuners. Let's
look at your Vee for a minute.

So my EZNEC on my future backyard Vee shows about 60ohm which is about
a 12:1 mismatch at the antenna feedpoint! So do I have something wrong
in the basic config? Or do you all put a balanced impedance
transformer up at the antenna feedpoint?

Assuming 50 feet of feedline a design center of 3800khz, and 31 ohms AT THE
RESONANT FREQUENCY (typical of a 90 degree vee), and a balanced tuner (for
the 450 ohm cases), you can expect feedline losses on the following order:

Belden 8240 (RG58) 0.344db
Belden 9258 (RG8X) 0.276db
450 ohm ladder line 0.102db

The coax losses above are at an SWR of 1.67 to 1, while the 450 ohm ladder
line loss is at 7.5 to 1.

Moral of the story. If you're only gonna use the antenna on 75m, use coax
and be done with it. It's not going to make much difference. BUT...

If you plan on using it on other bands, you might want to consider this:

160m (1.83mhz)

Belden 8240 25.61db (SWR 13000 at feedpoint)
Belden 9258 24.63db
450 ohm ladder line 6.69db (SWR a bit more than 1700)

40m (7.15mhz)
Belden 8240 8.4db
Belden 9258 7.52db
450 ohm ladder line 0.221db

Note that, even at the resonant frequency and a much higher SWR, the 450
ohm line has fewer losses (but not enough to matter). But where it really
shows up is when you try to use the antenna on bands well away from its
original design frequency.

Of course using an antenna on a frequency well above the design frequency
causes the pattern to break up. But that's the price of using a single,
untrapped wire on a lot of bands.


--
Dave Oldridge+
ICQ 1800667

jimg wrote:
so the question remains, ppl really run a very high swr at the
feedpoint..is there any advantage to matching at both point?

If you use ladder-line, you generally don't have to worry
about matching at the feedpoint. That's one of the advantages
of ladder-line. Ladder-line handles a 12:1 SWR just fine for
reasonable lengths.
--
73, Cecil http://www.qsl.net/w5dxp

jimg wrote:

Hi. I've heard and read some about ladder line and dipoles.
So what is the basic configuration look like? My impression is
the set-up starts with either a balanced tuner with 400 ohm output
or a 50 ohm tuner with a 4:1 balun to the 440ohm ladder line. The
ladder line then runs to the dipole and that's pretty much about it.

So my EZNEC on my future backyard Vee shows about 60ohm which is about
a 12:1 mismatch at the antenna feedpoint! So do I have something wrong
in the basic config? Or do you all put a balanced impedance
transformer up at the antenna feedpoint?

Just a little confuzed?


12:1 is just about right! What are you worried about? My VSWR on 80
meters is almost 30:1. I get excellent results.

VSWR is NOT bad. I know the Ham Mantra of low VSWR. But, it is a false
mantra. Once the antenna SYSTEM [antenna, feedline] is matched you get
maximum power transmitted to the load.

Hi Jimg,

Do not bother about the antenna impedance if you want to use it as a
multi-band antenna because it will change a lot with the frequency band.

1) First, install a dipole 2 x D, D being the higher length that can afford
your backyard. (2 x 20 m is good for 80m band operation)
http://www.barbaxoops.com/modules/xc...=7&pos=4&pid=4

2) Then you install the ladder (in the middle of the dipole). The ladder
should go straight from the center of the dipole to the antenna tuner (in
the shack). The ladder can be made of electric wires and PVC pipes as
spacers (do not forget to glue them)
http://www.barbaxoops.com/modules/xc...&album=7&pos=5
http://www.barbaxoops.com/modules/xc...&album=7&pos=2

3) Finally, you built an balanced antenna tuner. The F3LG type is the
easiest to built. The MacCoy (see the following pictures) is the most
popular
http://www.barbaxoops.com/modules/xc...&album=7&pos=0
http://www.barbaxoops.com/modules/xc...7&pos=1&pid=47

.... as you know, that antenna is called a "Center Feeded Dipole" .... but
french people say "Antenne Levy"

Contact me if you want more details about it.

Best regards

Jean-Marc
F4DRH
www.barbaxoops.com









Hi. I've heard and read some about ladder line and dipoles.
So what is the basic configuration look like? My impression is
the set-up starts with either a balanced tuner with 400 ohm output
or a 50 ohm tuner with a 4:1 balun to the 440ohm ladder line. The
ladder line then runs to the dipole and that's pretty much about it.

So my EZNEC on my future backyard Vee shows about 60ohm which is about
a 12:1 mismatch at the antenna feedpoint! So do I have something wrong
in the basic config? Or do you all put a balanced impedance
transformer up at the antenna feedpoint?

Just a little confuzed?


jimg
Oregon
USA