Hi Martin, You are using twinlead! A twinlead always acts as a transformer we call it lecher system, my dictonary believes you call it the same :-)
If you have a given impedance at one end, the impedence at the other end is depending on frequency and length of the Lecher wires. E.G. If the lenght of the lecher wires is exactly an electrically quarter of the wavelength, an open ended twinlead will show a short= Zero Ohms at the other end. Draw the current curve above the wire and you will understand it easier: A halfwave has zero current at the ends (0 current = high voltage = high impedance) and high current in the middle. At any point along the line you will have another impedance, thats the result of the transformed impedance at the feed point. By the way, thats the reason why lots of twin lead frieds use to have a 2-3m extra piece of twinlead in their bag if they are portable. If by chance the impedance on one band is transformed to a value the ATU cannot handle, they make the twinlead a little bit longer with this reserve piece and - bingo- the tuner now can handle the impedance. 72 de Peter, DL2FI www.qrpproject.de > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of Martin Gillen > Sent: Thursday, January 05, 2006 7:43 PM > To: elecraft@mailman.qth.net > Subject: Re: RE: [Elecraft] T1 Antenna Considerations > > Hi, Peter. > > Please excuse my ignorance I'm fairly new to amateur radio ;) > > But I have a question: > > > The only reason that the "use the nearby bushes" > > construct now can be tuned by the T1 is that the impedance goes low > > because a part of the antenna is lying "on the floor" now, > giving high > > capacitance against ground which allways lowers the impedance. > > Yes, I understand that; any radiation from the counterpoise > is effectively lost into the ground. > > However another antenna I have used is a 66ft length of wire > at 15feet, fed in the centre with 300 ohm twinlead. > > In this case, the driven half of the wire is still 33ft long > - but I get really low SWR om 20m and have worked DX with it, > > So why does that work? Is the feedline doing something to > help me out here? Or is a dipole just a completely different > scenario altogether? > > Thanks, > Martin. > > > > ___________________________________________________________ > Yahoo! Exclusive Xmas Game, help Santa with his celebrity > party - http://santas-christmas-party.yahoo.net/ > _______________________________________________ > 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 > _______________________________________________ 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
