Eric Gustafson wrote:
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.
Yes, read section 18 of the ARRL Antenna Book. It is the 'Optimized
Yagi' for 6 meters
>
>
> >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.
> Why is the answer 'Yes'?
> >Or should I suspect that all the baluns are bad?
>
> Can't say. Its a possibility. But...
I doubted it too...>
>
>
> 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?
I'm not sure what difference this makes. I swept the baluns from 1 to 100
mhz and reported the results at the best point.. abt 30mhz for most.
Worse at all others within that spectrum.
>
>
> Are you sure the Unidilla is supposed to be a 4:1 design?
That is what is marked on the Balun itself.
>
>
> >
> >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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