Balun question

[Vic K2VCO]

I made a simple 1:1 receive-only balun for 160 meters by winding 9 bifilar turns
of no. 24 enameled wire on an FT37-77 toroid.  I connected a 50-ohm resistor to
the output and my MFJ antenna analyzer to the input.  On 1.8 MHz it shows a
resistance of 50 ohms, an inductive reactance of 1 ohm, and an SWR of 1.0:1.

My question is, did I make a 'good' balun?  Are there other tests I should do?

It's job will be to isolate a receiving loop antenna from its feedline, to keep
the nulls deep and reduce noise pickup.

The RANT feature of the K2's 160-meter option has made it possible for me to use
a ferrite loop which is only 21 inches (53.3 cm) long and has a s/n ratio much
better than my inverted L transmitting antenna, even without the balun.  I'll
put details on my website after I finish testing it.

--
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco

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[Don Wilhelm-3]

Vic,

If my calculations are correct, YES you should have a good balun.  The
reactance of the 9 turns is 809 ohms (AL value is 884 mH/1000 turns,
inductance for 9 turns should be 71.6 uH) which is more than 16 times the
impedance of an antenna feedline of 50 ohms.  Greater than 10 times the line
impedance is the value I usually use for an effective chokeing action.

73,
Don W3FPR

> -----Original Message-----
>
>
> I made a simple 1:1 receive-only balun for 160 meters by winding
> 9 bifilar turns
> of no. 24 enameled wire on an FT37-77 toroid.  I connected a
> 50-ohm resistor to
> the output and my MFJ antenna analyzer to the input.  On 1.8 MHz
> it shows a
> resistance of 50 ohms, an inductive reactance of 1 ohm, and an
> SWR of 1.0:1.
>
> My question is, did I make a 'good' balun?  Are there other tests
> I should do?
>
> It's job will be to isolate a receiving loop antenna from its
> feedline, to keep
> the nulls deep and reduce noise pickup.
>

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[Vic K2VCO]

W3FPR - Don Wilhelm wrote:

> If my calculations are correct, YES you should have a good balun.  The
> reactance of the 9 turns is 809 ohms (AL value is 884 mH/1000 turns,
> inductance for 9 turns should be 71.6 uH) which is more than 16 times the
> impedance of an antenna feedline of 50 ohms.  Greater than 10 times the line
> impedance is the value I usually use for an effective chokeing action.

I connected the wires on either end together and tried to measure the
common-mode impedance.  It exceeded the range of the MFJ meter (650 ohms).  So I
guess that theory agrees with practice!

--
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco

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[n6wg]

Hi Vic
You can use your MFJ to measure the impedance of the balun.  Connect one of
of the balun (short both wires together) to the center of the MFJ coax
connector
and the other end, shorted together, to the shell of the connector.
Use the MFJ to measure the impedance of the inductor formed at the frequency
to be used, say 1850 kHz.  If the impedance is 5 or more times the 50 ohm
line impedance, you have a good balun for 160m.  If that is the only band
you
expect to use it on, you are done.

If you expect to use it over more bands, say 80 and 40m as well, tune the
MFJ
to those bands also and make the same neasurement.  With a good core, the
impedance
should hold through these bands as well, or even be higher.

Good luck and 73
Bob N6WG

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]]On Behalf Of Vic Rosenthal
Sent: Wednesday, April 06, 2005 3:39 PM
To: Elecraft Reflector
Subject: [Elecraft] Balun question


I made a simple 1:1 receive-only balun for 160 meters by winding 9 bifilar
turns
of no. 24 enameled wire on an FT37-77 toroid.  I connected a 50-ohm resistor
to
the output and my MFJ antenna analyzer to the input.  On 1.8 MHz it shows a
resistance of 50 ohms, an inductive reactance of 1 ohm, and an SWR of 1.0:1.

My question is, did I make a 'good' balun?  Are there other tests I should
do?

It's job will be to isolate a receiving loop antenna from its feedline, to
keep
the nulls deep and reduce noise pickup.

The RANT feature of the K2's 160-meter option has made it possible for me to
use
a ferrite loop which is only 21 inches (53.3 cm) long and has a s/n ratio
much
better than my inverted L transmitting antenna, even without the balun.
I'll
put details on my website after I finish testing it.

--
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco

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