Rob:
No, you don't actually open up the feedline. Each bulb is in parallel
with a section of feedline. This is a lot easier to do with open-wire
line. With window line, you have to strip the wire at each tap point, or
you could patch in a section of open wire line. A more modern approach
would be to build one of those inductively coupled current probes. I
think they are described in the Handbook and Antenna books.
Bob WB2VUF
"Rob Atkinson, K5UJ" wrote:
>
> Al,
>
> I'm a dim bulb (ha ha). What I think you are saying is get two plain old
> regular incandescent light bulbs, open up the feedline and connect each one
> in series with it, one on each side to force rf current through the
> filaments. Do I have this right? the part about spacing alligator clips is
> throwing me. don't see why that matters as long as the connection on one
> side is the same on the other.
>
> thanks,
>
> Rob
> K5UJ
>
> One extremely easy way to check current balance in the two wires of an open
> wire feedline which is used with balanced tuners is the following.
>
> Connect two pieces of about 12 inches of wire to a twist-on holder for a
> type 43 light bulb. Attach an alligator clip to the far end of each wire.
> Make two such assemblies.
>
> Connect one light bulb to each feedline wire. Start with connecting the two
> alligator clips close together and gradually increasing the spacing along
> the feedline until they start to glow with transmitted power. Make sure the
> spacing is equal on both feedline wires.
>
> You may have to increase the length of the connecting wires to the light
> bulbs or alternately, change the transmitted power in the feedline until you
> get a good indication.
>
> It is easiest to judge equal intensity if the bulbs just start to glow.
>
> CAUTION: Turn OFF the carrier when adjusting the clips along the wires!
>
> Intensity of each light bulb indicates current in the feedline. If both
> bulbs light equally then you have a good balanced feedline with equal
> currents in each leg.
>
> It's an old 1930's trick before the days of RG-8 and when RF meters were too
> expensive for most hams.
>
> 73. Al, w6wqc
>
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