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From: Bob W5WSS
Date: 08 May 2003
Time: 10:05:37
Remote Name: 64.12.96.39
Thanks Bill,i checked out the w7el site and find it very useful,although admittedly i will need some time to learn to use it!I have been experimenting empirically with this indoor antenna for about 3-weeks and must say it is interesting.Bill if you find time to model this antenna the band of most interest is 20mtr.the feedline is 300 ohm flatline.the exact feedline length is 5'11".velocity factor unknown.the two halves of the doublet are exactly(i measured it today)44'.the wire diameter is 1/16" copper.and as veiwed as a bi-square the open ends are simply moved apart at right angles by about 2".currently i am using this antenna "as is"without the aid of an antenna tuner.The rig is a Kenwood 820s with tube finals and utilizes a pi- network to match the 6146's cathode resistance to the conjugate of the ZO load.Bill this is the first time i needed to think outside the "resonance box" This conjugate match in conjunction with the pi- network is actually happening and really is allowing the antenna to radiate practicaly all of the rigs inherent 100w pep.because the feedline run is so short the losses are so low that the additional losses introduced by the large mismatch is less than detrimental..incidently the rig is running as cool as if it were looking into a purely resistive 52ohm zo.this is accomplished via dipping the plate current and maintaining a rated idling current of 60ma with the transmitter keyed in ssb.this translates to apx.250ma when the ssb transmitter is modulatd.right on spec!as a double check i used an rf wattmeter connected at the antenna and see the additional power(the sum of the two but in reality the output is 100w it really is amazing!this is how i know the rig is actually transmitting 100w.and is the first time i have seen the technique of conjugate match..historicaly i have always been able to make my outdoor antennas surge impedence close to 52ohms.However this case is different.I plan to fabricate an efficient transmatch for the purpose of providing a proper termination for a low pass filter.Bill i will not be able to use higher power levels very often due to exposure issues but i see no reason beyond breakdown tolerances that i couldnt.One area of interest is in evaluating the differences that coaxial cable would present as a very short feedline as opposed to the 300 ohm flatline beyond the obvious of lineloss calculations.i am thinking of comparing the two and will seek the line which minimizes my exposure level since the rig places me right close to the feedline.I am apx 10' from any point along the feedline.I may choose to grudgingly sacrifice some toa for safety!grr.Bill if you are able to model the differences offered by an electrical duplicate of coaxial cable as feedline that would be interesting.Well thanks for the reply and just to be sure i am assuming no moral obigation on your part to model this antenna except out of common interest.regards Bob Morris W5WSS