Seeing the Effect of a Resonant Antenna

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N7AIG
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Joined: 2010/06/17 - 08:10
Seeing the Effect of a Resonant Antenna

This is interesting... This morning I took some old RG-58 Ethernet cable that I had laying around and made a 30m HW Dipole out of it. Mounted outside, along N-S direction, at the edge of our overhanging roof at about 10 ft elevation - in addition to our home elevation on the top of a hill in Tucson at around 2900 ft ASL. (No trees to hang from)

New antenna resonates around 10.3 MHz, but very broad, and has SWR of 1.5 across the entire 30m band. So looks close to the expected values.

[ For reference, the velocity factor in the RG-58 coax shield is empirically determined to be around 0.89, not the 0.95 one assumes for thin-wire. ]

Had been using a junk dipole located about 10 feet from the new one, but resonant at 8 MHz, and slight V-pitch to get some North-South coverage. Old antenna was tuned to 10.140 MHz with a T-network matching unit.

New dipole loses the North-South (to Alaska) somewhat. But overall, I gained about 1 S-unit of background noise quieting, and approximately 10 dB of improvement in beacon reception SNR in the E-W directions. Using the T-network tuner to get 1:1 SWR, but that probably isn't necessary.

Basically, I attribute the improvement to the effects of using a resonant antenna, compared to a non-resonant structure through a matching unit. The resonance helps boost the weak signals coming in. And doubtless, also helps the transmitted signal, but the effects here are less clear since 1 Watt out is radiated with the help of the matching unit, regardless of the antenna resonance.

de N7AIG