If one has a sealed balun, such as you would pick up at your FLARPS or a
fles market, and the label has disappeared from environmental exposure,
is it possible to easily determine -

1) - if you are sure it's a 1:1 whether it's voltage or current type

2) - given it's totally unknown, anything about it.

Instruments available would be a standard multimeter and an MFJ 259 or
something equivalent.

I think I know the answer to 1), but 2) has me stumped. Yes, dummy
loads are a start, but is there an efficient way to get all unknowns
absolutely resolved.

tom
K0TAR

Tom Ring wrote:
If one has a sealed balun, such as you would pick up at your FLARPS or a
fles market, and the label has disappeared from environmental exposure,
is it possible to easily determine -

1) - if you are sure it's a 1:1 whether it's voltage or current type

Measure between the input terminals with an ohmmeter. A voltage balun
will show a DC short, a current balun an open.

2) - given it's totally unknown, anything about it.

Connect the input terminals together and the output terminals together.
Connect it to your antenna analyzer as a plain series load -- that is,
connect the balun input terminals to the analyzer center conductor and
the balun output terminals to the analyzer connector shell (or reverse
the two -- it doesn't matter). Measure the impedance at frequencies of
interest. You generally need a minimum of around 500 - 1000 ohms for an
effective balun. The angle of the impedance doesn't matter unless you're
running a lot of power, in which case a low angle (that is, a primarily
resistive impedance) might result in objectionable balun heating.

You can also connect resistors of various values across the balun output
and measure the input Z with your analyzer. With a 50 ohm load, you
should see close to 50 ohms in over a wide frequency range. As the load
gets farther from 50 ohms, you'll see more variation between the input
and output Z and it'll change more rapidly with frequency. This can be
corrected if necessary with a matching arrangement.

Instruments available would be a standard multimeter and an MFJ 259 or
something equivalent.

I think I know the answer to 1), but 2) has me stumped. Yes, dummy
loads are a start, but is there an efficient way to get all unknowns
absolutely resolved.

Roy Lewallen, W7EL

"Tom Ring" wrote in message
.. .
If one has a sealed balun, such as you would pick up at your FLARPS or a
fles market, and the label has disappeared from environmental exposure,
is it possible to easily determine -

1) - if you are sure it's a 1:1 whether it's voltage or current type

2) - given it's totally unknown, anything about it.

Instruments available would be a standard multimeter and an MFJ 259 or
something equivalent.

assuming its a wound balun...
attach some alligator clips to a variable resistor, and set it to around 50
ohms or so - then attach it to one side of the balun. and attach coax from
the mfj259 to the other side.
turn on the mfj and adjust the resistor for low swr (you'll have to measure
it later)
turn it off and measure the resistance you had to adjust it to.
Dividing that value by 50 will probably be the balun's impedence ratio
(4-to-1 - or whatever)
Change freqs on the MFJ and go it over again till you determine the
bandwidth.
(If you adjusted the resistor to 200 ohms and it shows SWR of 1:1, then its
a 4 to 1 balun)
my 2¢
Hal
W4PMJ

Correction:

Roy Lewallen wrote:
. . .
Connect the input terminals together and the output terminals together.
Connect it to your antenna analyzer as a plain series load -- that is,
connect the balun input terminals to the analyzer center conductor and
the balun output terminals to the analyzer connector shell (or reverse
the two -- it doesn't matter). Measure the impedance at frequencies of
interest. You generally need a minimum of around 500 - 1000 ohms for an
effective balun. The angle of the impedance doesn't matter unless you're
running a lot of power, in which case a low angle (that is, a primarily
resistive impedance) might result in objectionable balun heating.
. . .

This test works only with a current balun. If done with a voltage balun,
the impedance should be very low.

Although there are ways to test for the proper functioning of a voltage
balun, that is, to test for the voltages at the output terminals being
equal and opposite with respect to the "cold" side of the input, they
don't tell you how effective it'll be in stopping common mode currents
on feedlines. In fact, certain imperfections might improve the
performance of a voltage balun in that application. I don't recommend
using a voltage balun for feeding antennas for the reasons I gave in
http://eznec.com/Amateur/Articles/Baluns.pdf.

I apologize for the error. Thanks very much to Owen Duffy for pointing
it out to me.

Roy Lewallen, W7EL

Roy Lewallen wrote:

This test works only with a current balun. If done with a voltage balun,
the impedance should be very low.

Although there are ways to test for the proper functioning of a voltage
balun, that is, to test for the voltages at the output terminals being
equal and opposite with respect to the "cold" side of the input, they
don't tell you how effective it'll be in stopping common mode currents
on feedlines. In fact, certain imperfections might improve the
performance of a voltage balun in that application. I don't recommend
using a voltage balun for feeding antennas for the reasons I gave in
http://eznec.com/Amateur/Articles/Baluns.pdf.

I apologize for the error. Thanks very much to Owen Duffy for pointing
it out to me.

Roy Lewallen, W7EL

Thanks for the replies, Roy. They were pretty much what I suspected,
but hearing it from you is a nice confirmation. Why don't you make a
small white paper on your site covering this subject?

As usual, I didn't get my original post, and none of the replies, except
for this one. It's nice to have google to pick up what my newsfeed misses.

tom
K0TAR