Web Updated;
06/07/2011
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Installation and Adjustments
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The Completed dipole was set up running the length of our
house, and connected to the Radio
Solutions Mini VNA.
The initial reading were approx 1:2.2 on VSWR and 70-72 Z-Ohms. The overall length was too long so I bent back and wrapped around the 2.5mm˛ insulated tails reducing them to a length of approx 1.5m. This brought the antenna to a resonance of 1:1.5 with a Z Impedance of approx 72 Ohms. I thought that this would be good enough for starters, not withstanding that the antenna was fairly capacitive as so close to the ground.
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| The antenna was erected in my loft space which is only 6m
End to End.
This obviously meant that the ends of the antenna needed to be dog legged down to enable the tails to fit! As the impedance is approx 70-72 Ohms I fed this antenna with 75 Ohm RG6/U Satellite cable with 10 turns around a 120mm former at the feed point as a choke. After the tails had been installed onto insulators vertically down from the dipole level I re set the Mini VNA to work. Interestingly, possibly due to the vertical down section of the tails and also parasitic effects from the other antenna within the space the frequency had shifted up band by approx 250 KHz, thus I lengthened the tails to an overall dimension of 1.75m. This brought the resonance down to 7.1MHz with a centre band VSWR of better than 1:1.25 |
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