Re: [Elecraft] Re: may have it wrong
In a message dated 6/17/05 11:03:26 AM Eastern Daylight Time, [EMAIL PROTECTED] writes: Jim N2EY wrote: On 40 meters, the feedpoint impedance will look like a resistance of a few ohms and a reactance of several hundred ohms or more. Will the matching network be able to handle that, and do it without undue loss? The impedance at the center of a 33 foot doublet on 40 meters will be about 12-j850 ohms. Yes but what was described wasn't a doublet up in the air. IIRC, he wasn't using a feedline, so one end of the wire is close to the ground and the rig. More like a semivertical with one radial. 73 de Jim, N2EY ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
RE: [Elecraft] Re: may have it wrong
Wayne N6KR wrote: ...what you described won't work very well, because both wires need to be about 33 feet long at this frequency. By cutting one 33-foot piece of wire in half, you've made a 20-meter antenna :) A modeling program like EZNEC predicts that a 33-foot center fed wire will show a gain of about 6.9 dbi on 7 MHz and about 7.1 dBi on 14 MHz. That's essentially no difference at all. That's at a height of about 30 feet where the antenna's main lobe is straight up for short skip work on 40 and down around 30 degrees on 20 - useful for DX ing. The difference remains on the order of 0.1 or 0.2 db between 40 and 20 all they way down to under 15 feet, where ground absorption will start to show a significant loss on 40 due to the low height of the antenna. That miniscule difference in performance between a half-size and full size doublet agrees with what many handbooks, including the ARRL handbook, has claimed for many years. Of course, that assumes no difference in matching network losses, which I'd not expect a KX1 user to see using such an antenna without a feed line. (Of course, if a coaxial feeder is used, then some means to holding down the SWR on the feedline is very important to avoid losses there.) I was concerned that the tuner in the KX1 wouldn't be able to handle the high impedance of a 1/2 wave (33 ft) wire on 20 meters. Ron AC7AC ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
Re: [Elecraft] Re: may have it wrong
In a message dated 6/17/05 2:12:37 AM Eastern Daylight Time, [EMAIL PROTECTED] writes: Wayne N6KR wrote: ...what you described won't work very well, because both wires need to be about 33 feet long at this frequency. By cutting one 33-foot piece of wire in half, you've made a 20-meter antenna :) A modeling program like EZNEC predicts that a 33-foot center fed wire will show a gain of about 6.9 dbi on 7 MHz and about 7.1 dBi on 14 MHz. That's essentially no difference at all. Of course, that assumes no difference in matching network losses, which I'd not expect a KX1 user to see using such an antenna without a feed line. (Of course, if a coaxial feeder is used, then some means to holding down the SWR on the feedline is very important to avoid losses there.) There's more to it, though: On 40 meters, the feedpoint impedance will look like a resistance of a few ohms and a reactance of several hundred ohms or more. Will the matching network be able to handle that, and do it without undue loss? 73 de Jim, N2EY ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
RE: [Elecraft] Re: may have it wrong
Jim N2EY wrote: On 40 meters, the feedpoint impedance will look like a resistance of a few ohms and a reactance of several hundred ohms or more. Will the matching network be able to handle that, and do it without undue loss? The impedance at the center of a 33 foot doublet on 40 meters will be about 12-j850 ohms. I would expect the KX1's ATU to match that without problem. However, Wayne pointed out off the reflector that I was making a rash assumption: Mike did *not* say he had an ATU! Without the ATU it's very important to provide a decent match to the KX1 output of course. That's why Wayne said to use a self-resonant 66 foot dipole. So Mike, if you didn't include the KXAT1 internal ATU or a T1 external ATU, maybe this is the time to add one! It's not a requirement, but if you don't use one you'll need to make sure to have a low SWR at the rig with any antenna you use in order for it to work very well. Ron AC7AC ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
