Why not just measure the RF Voltage on the balanced tuner output or balun
with the antenna connected and the transmitter producing steady carrier?
Much easier to do, no guesswork.
Now this gets into the discussion of "is the antenna a true balanced load?"
Even though the wire lengths are exactly the same, the feed is installed so
that nearby objects do not unbalance it, and the legs of the antenna are
equal distances above ground with no trees, houses and etc between it and
terafirma, it will come close to balance. This also presumes that the legs
are 180 degrees apart.
>From a practical point, don't bother worrying about it. In my case I have 2
Westinghouse RF amp meters, 1 in each side of the balanced feed. Some days
they show balanced currents and some days they show a small difference.
Being blessed with a vector voltmeter, I can measure the RF voltage and the
phase between the two sides of the feedline. As long as the phase stays 180
degrees difference, which it always does, then the balanced tuner or balun
is doing its job even though the RF volts may be different. Station works
just the same either way.
73
Bob, K4TAX
----- Original Message -----
From: "Bwana Bob" <wb2vuf@qsl.net>
To: <tentec@contesting.com>
Sent: Tuesday, July 15, 2003 5:32 PM
Subject: Re: [TenTec] balanced feedline light bulb test
> 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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