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| To: | <[email protected]> |
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| Subject: | LF: Re: Arcing relays &c. |
| From: | "James Moritz" <[email protected]> |
| Date: | Wed, 12 Oct 2011 09:59:21 +0100 |
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| References: | <[email protected]> <[email protected]> <[email protected]> <[email protected]> <[email protected]> <1849736542-1318171189-cardhu_decombobulator_blackberry.rim.net-208700020-@b1.c11.bise7.blackberry> <FB0006513E634A96AFED8066F7C344C1@JimPC> <[email protected]> <BA4122BA92D44641A1BE5ED27FD763E5@JimPC> <[email protected]> <[email protected]> <[email protected]> <006c01cc87ab$427234c0$4001a8c0@lark> <[email protected]> <834DCCD1D3834F4CB4C171B7C30E85B4@AGB> <004801cc8809$63378d50$4001a8c0@lark> <C141E3F03F9B47FA80F4461CE4B174BC@AGB> <[email protected]> |
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Dear Joe, LF Group, Feeding this into 3 mH (X=2500 ohm at 137.8 kHz) gives 11.2 kV (17 kV peak) so relays in series as suggested by G8FZK and G3NYK should workwell. It is a bit more complicated than that... if you have a number of relays in series, when the contacts are open there will be one or more isolated "floating" sections of conductor linking the open contacts. To ensure that the voltage is evenly distributed between the relay contacts, you would need to take steps to ensure that the potentials of these isolated sections are equal divisions of the total antenna voltage - this would mean adjusting the distributed capacitance in the relay wiring somehow. Also, the relay at the "hot" end will have the entire antenna voltage between contacts and coil, so coil-contact breakdown voltage would need to be much higher than the voltage rating for the contacts. I'm puzzled by the 6pf/metre rule for monoploes. It seems the capacitance of the monopole is much higher. This is a good first-order estimate for wire antennas - it is reasonably accurate for wires up to a few mm in diameter, but if the antenna element is a conducting mast, the diameter will be much larger, and C significantly higher too. Cheers, Jim Moritz73 de M0BMU |
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