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| To: | <[email protected]> |
|---|---|
| Subject: | LF: Re: Re: TX system at DK7FC, schematic |
| From: | "James Moritz" <[email protected]> |
| Date: | Sun, 18 Dec 2011 10:58:28 -0000 |
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| In-reply-to: | <002c01ccbd6f$572761c0$0401a8c0@xphd97xgq27nyf> |
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| Sender: | [email protected] |
Dear Mal, LF Group, I can see you resonate your 3mH coild with a motor driven variometer but howdo you match this to exactly 50 ohmz for a SWR of 1:1 to the TXI can see your coil and transformer secondary are in series to earth but noadjustment for matching. Essentially the same arrangement is in use here. The transformer ratio is adjusted to match the antenna resistance to 50ohms. A Q of 1000 is typical for a coil of this size wound using Litz wire. You might increase that somewhat by optimising length, diameter, winding pitch etc. For something big like the Balboa loading coil in Alex's mail, Q can be considerably higher - Watt's "VLF Engineering" has data on this particular antenna system - the coil resistance at 25kHz is about 0.06ohms, and the reactance 225ohms, making the Q about 3800 - it might be higher at 136k, since reactance often increases faster than loss resistance as the frequency goes up. Incidentally, I estimate L of the main loading coil about 1.3mH, so GW0EZY would need the variometer in series as well ;-) Cheers, Jim Moritz 73 de M0BMU |
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