To: <towertalk@contesting.com>
>Date: Sun, 11 Apr 1999 17:12:27 -0400
>From: Joe Shuey NE3H <ne3h@access.webcombo.net>
>
>I am building a 6 meter beam. I decided on the Antenna book
>arraingement of feeding this Yagi with a Hairpin match and a 4:1
>balun.
Does the ARRL book really recommend a 4:1 balun with a hairpin
match? I'd expect this to be a 1:1 balun.
>I have 3 baluns on hand. One is an UNADILLA ( unused ), the
>second looks very much like the first, but is used and the 3 is
>one I purchased as part of a 15 mtr monoband antenna with no
>outside markings.
>
>I hooked up my old Network Analyzer and a Directional Coupler. I
>terminated the Baluns with a 200 ohm metal film resistor. When
>swept up to 100 mhz, the best return loss was, perhaps 12db. I
>expected greater than 20db. I thought perhaps, that I had an
>improper setup.
>
>SO I got out the trusty AEA analyzer. I checked on 21 28 and 50
>mhz. The best SWR that I could get was not reasonable. The best
>match I could get was with a 400 ohm load on 50mhz .. and that
>was 1.8:1.
>
>Is it unreasonable to expect a decent reading with such low
>power?
Yes.
>Or should I suspect that all the baluns are bad?
Can't say. Its a possibility. But...
Have you tried them with truly balanced (as opposed to floating)
loads? For example, referenced to a conductive plane, ground the
coax shield at the balun input and connect 100 ohms from each
wire of the balun output to ground?
Are any of them designed for operation above 30 MHz?
Are you sure the Unidilla is supposed to be a 4:1 design?
>
>I expect that I could build a half wave transmission line and
>get return losses of greater that 30db.
>
>What's wrong here?
I wouldn't expect any of these things to work much beter than 12
to 15 dB return loss into a resistor (non-inductive resistor?) at
6 meters due to lead inductances at the balun to resistor
connection.
73, Eric N7CL
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