Is there a means of testing a 9:1 or 10:1 balun to make
sure it is the correct impeadance before connecting it to
an antenna or tuner?

"Radio Man" wrote in message
news:XVo3d.473$C8.256@trnddc05...
Is there a means of testing a 9:1 or 10:1 balun to make
sure it is the correct impeadance before connecting it to
an antenna or tuner?

If at a low frequency , put a resistor across the high impedance of the
balun equal to the design impedance and check the swr. Frequency does not
really have anything to do with it, just it is sometimes hard to get a
resistor that is not reactive and is acting like a resistor at the higher
frequencies.

Build 2 of the baluns and connect them back to back and put a 50 ohm dummy
load on the second one, assuming you are going from 50 ohms to the 450 or
500 ohm impedance unbalanced. Then measuer the swr.

Dont know how useful this would be but it might be worthwhile measuring
the RF power on the input and output side of the balun in the back to
back exercise. That will give you an idea of loss and as you increase
power, saturation.

Cheers Bob VK2YQA



Build 2 of the baluns and connect them back to back and put a 50 ohm dummy
load on the second one, assuming you are going from 50 ohms to the 450 or
500 ohm impedance unbalanced. Then measuer the swr.

I had not thought of the losses that can occur in terms of db I wonder what
sort of losses occur due to the use of baluns?
Art

"Bob Bob" wrote in message
...
Dont know how useful this would be but it might be worthwhile measuring
the RF power on the input and output side of the balun in the back to
back exercise. That will give you an idea of loss and as you increase
power, saturation.

Cheers Bob VK2YQA



Build 2 of the baluns and connect them back to back and put a 50 ohm
dummy
load on the second one, assuming you are going from 50 ohms to the 450
or
500 ohm impedance unbalanced. Then measuer the swr.

I guess you could say that once they saturate magnetically more power
from that point on will be a loss grin

Resistive wire losses as well. ie the balun gets hot (Altho saturation
also leads to temperature rise)

I am not that knowledible of baluns but note that the number of turns is
a compromise of sorts. The Xl is suppose to be some multiple of the Zo
and Zi (10x I think is a good number) Too high a number of turns and it
saturates at a lower power, too low and resistive losses become a factor..

I am prepared to be shot down on this.. I learn as I need to!. ie When I
need a balun I'll read up on them...!

Cheers Bob VK2YQA


wrote:
I had not thought of the losses that can occur in terms of db I wonder what
sort of losses occur due to the use of baluns?
Art

Radio Man wrote:

Is there a means of testing a 9:1 or 10:1 balun to make
sure it is the correct impeadance before connecting it to
an antenna or tuner?

Couple ways-- Requires non inductive resistor -- If have a
MFJ-259 (ect) or a Noise bridge, connect your resistor to the X9
output side of the balun, connect the input side of the balun
to the MFJ, and sweep the frequencies, -- the meter should
stay FLAT, at 1:1 (or close to it) over the range it is designed for.
or, the noise bridge noise level should remain unchanged (same consider
ation). or, (this requires a POWER, NON-inductive resistor),
with a SWR bridge, XMIT into it (again on various freqs)!!
SWR should be flat over the range you want to use! Jim NN7K

Couple ways-- Requires non inductive resistor -- If have a
MFJ-259 (ect) or a Noise bridge, connect your resistor to the X9
output side of the balun, connect the input side of the balun
to the MFJ, and sweep the frequencies, -- the meter should
stay FLAT, at 1:1 (or close to it) over the range it is designed for.
SWR should be flat over the range you want to use! Jim NN7K

That's the way I have checked impedence transformers in the past.
I have found that a Variable resistor works pretty good for testing with a
MFJ-259.
Used it for half-wave coax baluns, as well as wind-it-yourself transformers.
Set the variable resistor to the expected value to match, then check it with
the MFJ-259,
it worked for me - on hf and 2-meters. Didn't try it on the uhf freqs.
I used to like to use 300-ohm twinlead because the weight didn't make the
dipole sag as much as coax.






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