BL2 Balun Question

[Terry]

I have the BL2 Balun and use it for balanced lines to Coax.  Occasionally,
when I am using a wire and counterpoise to the BNC binding posts, I try to
match a shorter wire for 80 meters than what I really should due to lack of
space in RV sites.  I believe I am connecting the Balun correctly; hooking
the long wire to A and the counterpoise to B on the Balun inputs.  I can get
a shorter wire to tune that way.

 

My question is:  what is the purpose of the GND connection on the Balun?
Does it need to be grounded when in use?  Looking at the circuit diagram in
the manual, I don't think the counterpoise should be attached to the ground
connection?

 

I'd be interested in how others hook up their BL2 Baluns.

 

Thanks and 73's,

 

Terry de N7TB

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[Bob McGraw - K4TAX]

Your operation is similar to one I encounter when operating from our RV.

A balun has several primary and in may cases mutiple functions. Some,
all or none may be contained in the specific balun design:

(a) operation between a balanced and an unbalanced circuit. Hence BalUn
meaning balanced to unbalanced.  This is typical where the coaxial
unbalanced output of a transceiver is connected to a balanced load such
as a balanced antenna which is fed with balanced line.

(b) a balun can offer impedance transformation characteristics such as
found with a 4:1 or 6:1 or other transformation ratios. In the case of a
4:1 balun it transforms a 200 ohm balanced load to a 50 ohm unbalanced
source.   Optimum results attained here would with a folded dipole
design offering some 200 to 300 ohm load being transformed into a 50 to
75 ohm source.

(c) Correctly designed a balun should offer some degree of common mode
current rejection.  Thus the reduction of common mode currents induced
into the feed line thus flowing back into the station equipment.

In your case the use of the balun between the transceiver to the
balanced feed line is correct.  Then the "ground" terminal should be
connected to the transceiver reference ground point.  Ideally a driven
ground, although in a RV perhaps just the metal framework of the
vehicle.   As to using a wire, yes connect the random length of wire to
terminal A and If you use a counterpoise, be it elevated on on the
ground as in a radial field, then it can connect to terminal B.  In this
case the counterpoise should be connected to "ground".  The application
of the balun in this configuration is then simply to prove some
impedance transformation as in a 4:1 balun and to control common mode
current.   That is provided the balun is correctly designed for such.

In the case of the BL2 balun, it is switchable between a 4:1 ratio and a
1:1 ratio.  Your specific application will likely require the use of
either at one time or another depending on your antenna configuration.

My personal reference for this discussion and balun designs in detail
can be found at the DJ0IP website. http://www.dj0ip.de/balun-stuff/
<http://www.dj0ip.de/balun-stuff/>


73

Bob, K4TAX


On 6/8/2017 11:47 AM, Terry Brown wrote:

> I have the BL2 Balun and use it for balanced lines to Coax.  Occasionally,
> when I am using a wire and counterpoise to the BNC binding posts, I try to
> match a shorter wire for 80 meters than what I really should due to lack of
> space in RV sites.  I believe I am connecting the Balun correctly; hooking
> the long wire to A and the counterpoise to B on the Balun inputs.  I can get
> a shorter wire to tune that way.
>
>  
>
> My question is:  what is the purpose of the GND connection on the Balun?
> Does it need to be grounded when in use?  Looking at the circuit diagram in
> the manual, I don't think the counterpoise should be attached to the ground
> connection?
>
>  
>
> I'd be interested in how others hook up their BL2 Baluns.
>
>  
>
> Thanks and 73's,
>
>  
>
> Terry de N7TB
>
> _

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