Phil says:
>How can I test it to assure balanced output into my open-wire
>feeders?
Best bet is to measure the current in the two feedwires. If you have 2
identical RF ammeters, put one in each leg and measure the currents. Now
swap over the meters (the one in the right hand leg goes in the left and so
on) and measure again. If the results are the same in each leg, you're OK.
If the answers are unbalanced in both cases, but the unbalance follows the
meters, you're OK.
If you haven't got a pair of ammeters, get some flashlamp bulbs - the really
low power 2.5 volt ones. A couple of clip leads so you can clip them across
about 2 or 3 feet of feeder line, and they'll indicate the current. (i.e. on
the one feeder wire, coonect the bulb between two points two or three feet
apart - not across the feeder line). Fix a bit of wood so you can have the
bulbs with a bit of paper midway between them: put a drop of oil on the
paper, and when (if!) the bulbs are equal brilliance, it will apparently
disappear (the grease spot photometer). If the feedpoint is really high
impedance, and the current too low even at full power to light the bulbs,
put the bulbs in series with the feeder wires.
It may be worth swapping the bulbs between legs as a check that they show
equal brightness at equal currents.
You can also try measuring the voltages with a suitable RF voltmeter, but
that's a more difficult process, especially at high impedance where the
capacity of the voltmeter input can throw things off.
Finally, I wouldn't worry about any unbalance less than 10%, and in
practice, I'd accept up to 25%. Bear in mind that the feeders need careful
dressing for symmetry.
73
Peter G3RZP
> ----------
> From: Phil Clements[SMTP:philk5pc@tyler.net]
> Sent: 21 June 1999 03:27
> To: amps@contesting.com
> Subject: [AMPS] Testing for Balanced Output from antenna Tuner
>
> I have just constructed a copy of the antenna tuner featured
> on the cover of the 1999 ARRL Handbook.
>
> How can I test it to assure balanced output into my open-wire
> feeders? I have never used a "T" type transmatch with the balun
> on the 50 ohm input side before and I want to make sure it is
> truly balanced.
>
> (((73)))
> Phil, K5PC
>
>
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