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