Alex,
Hi again,
1. .25WL of 70 ohm RG11 coax. Make sure you consider the velocity
factor of the coax when you cut it to length.
If you use RG11 with a VF of .667, then 11 feet is approximately the
correct length. You can cut it a little long, put on a PL259 on one
end and use an SWR bridge (MFJ259 works well) You will find a dip in
impeadance. Trim until you move the dip to 14.15 Mhz. The dip will
be very broad and cover the whole band well. Then put the other end at
the feedpoint of the loop. Discard the gamma match stuff. Coil the
coax so it is in a linear coil. Use a PVC form like a 5 inch PVC pipe to
create the balun.
2. Gamma match, These are a little tricky to get to work with just
wires. Most require a capacitor in series with the gamma wire.
Forget it and use the coax trick to match your loop.
Jay
IZ4EFN - Alessio wrote:
>
> Thanks Jay, you really helped us cause many books talks about this 70-75
> Ohms 1/4 WL balun at the feedpoint, but no one of the time had ever had
> enough courage to try that! :-)
>
> Gonna see tomorrow nigth!
>
> I also wanna ask you this:
> according to a project published in an Italian manual we fixed a gamma match
> on one side of the radiating element.
> It's 89cm long and we introduced in it the central conductor of the coax,
> for all the length of the gamma match, without ANY electrical connection
> with the antenna, as the amnual says, something as a capacitor.
> After that, we connected the ground of the coax to the boom of the entire
> antenna.
>
> Moving the gamma match, the spacings, the legth of the cable inside it,
> never seemed to let the ratio move or change neither in some little low
> ratio (2,5...not so weak...) spikes frequency...
>
> Do you think we doing something wrong?
>
> Thanks and sorry for the bad English!
>
> Alex.
>
> > A single loop will have an impeadance of 110 +j0 ohms at resonance.
> > Use a .25WL 70 ohm transmission line to feed it, coiled as a balun at
> > the feedpoint. and you should be able to get it to become a 1:1 SWR.
> >
> > Jay, WX0B
> >
>
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--
Jay Terleski
Array Solutions
972 203 2008
Military Communications Systems, Phased Arrays, RF Switches, Antennas &
Towers
http://www.arraysolutions.com
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