Just put up a 140' dipole with 450 ohm ladderline feed.

I'm using an unbalanced tuner with a Spi-Ro 1:1 balun on the output side of
the tuner. The balun is one of those designed to be used right at the
center feed point of the antenna, with coax as the feedline. I think it
should work out fine being directly at the output of the tuner, with
ladderline going up to the antenna.

However, there is some disconnect between the rig and antenna. I suspect my
balun may be bad internally. What's a good quick and dirty check with an
ohmeter (don't know if these baluns are current or voltage types, so maybe
include a checkout procedure for both kinds).

I'm just starting to fault isolate. Since the balun is a new link in the
chain from rig to antenna, it's my first suspect.

With a current balun, you should have continuity from the feedline
conductors to the antenna conductors just as though the balun were a
couple of pieces of wire connecting the feedline directly to the
antenna. There shouldn't be any continuity from one side of the antenna
or feedline to the other.

A correctly operating voltage balun will show continuity between any
pair of conductors, input to input, output to output, or input to
output, just as though they were all shorted together inside. If there's
an internal short where it shouldn't be, you won't be able to determine
it with an ohmmeter. But you'd be able to see an open connection.

You won't be able to tell a short-circuited current balun from a
normally operating voltage balun with an ohmmeter, either.

Using the balun as you are might cause its destruction. If the impedance
seen at the input of the ladderline is very high (which is particularly
possible if you're using the dipole on multiple bands), the voltage
appearing across the balun might well be more than it's designed to
handle. There are also likely to be common mode impedances on some bands
that will be too high for the balun to be effective. Moving the balun to
the antenna will change the bands where those conditions exist, but
won't necessarily alleviate them -- assuming you're using the dipole on
multiple bands, that is. You might consider taking a look at Cecil's web
site for some alternatives.

Roy Lewallen, W7EL

RB wrote:
Just put up a 140' dipole with 450 ohm ladderline feed.

I'm using an unbalanced tuner with a Spi-Ro 1:1 balun on the output side of
the tuner. The balun is one of those designed to be used right at the
center feed point of the antenna, with coax as the feedline. I think it
should work out fine being directly at the output of the tuner, with
ladderline going up to the antenna.

However, there is some disconnect between the rig and antenna. I suspect my
balun may be bad internally. What's a good quick and dirty check with an
ohmeter (don't know if these baluns are current or voltage types, so maybe
include a checkout procedure for both kinds).

I'm just starting to fault isolate. Since the balun is a new link in the
chain from rig to antenna, it's my first suspect.

Wow! Good info, Roy. Thanks. That should get me going, at least.

Roy forgot to mention / stress that a balun is designed for specific
impedances. If it is a common 1:1 balun, then it is probably designed for
50 ohms. They are designed for feeding a 1/2 wave dipole or similar
antenna, not widely different (from 50) impedances.

Steve, K,9.D;C'I

"RB" wrote in message
...
Wow! Good info, Roy. Thanks. That should get me going, at least.