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| Subject: | Re: LF: Re: MiniWhip antenna, fiber optic TEST SIGNALS NEEDED on 630m WSPR |
| From: | Stefan Schäfer <[email protected]> |
| Date: | Sun, 14 Jul 2013 01:08:15 +0200 |
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Hello Hideho,Thank you. I hope to continue tomorrow or so. I have prepared a list of experiments that i want to do :-) Am 13.07.2013 20:18, schrieb Hideho YAMAMURA: It depends on the grounding situation. If the whip is grounded at the top of the pole and the pole is connected to a clean RF earth and the coax is connected to a noisy shack earth, then the common mode chokes will probably help. But if the whip is only grounded by the coax in the shack, there will be no difference, at least no significant. And the coupling capacity between the windings of an isolation transformer can easily reach the order of magnitude of the probe, i.e. a few pF....[...] Last year, I made a Mini-Dipole with an instrumentation amplifier AD8429 set at Av=10 (+20dB), which worked fine, and is in current use. The dipole elements are aluminum L shape angles, 50cm long each. I noticed that adding common-mode chokes, LPF on the coax, isolation transformer to the RX gave no improvement of signal to noise ratio, but on the Mini-Whip they slightly did. I interpret this that the mini-DP is more immune to coax induced noise. 73, Stefan/DK7FC |
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