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From: Bob Morris W5WSS
Date: 02 May 2003
Time: 04:49:40
Remote Name: 152.163.189.173
I built a pretty interesting indoor antenna that is working reasonably well.And i thought i would share the following with all of you fellow antenna enthusiasts!The empirical evolution resulted in a variation that warrants interest.The dimensions are as follows:wire size#22solid copper,wire length apx.80ft. fastened to the point at which the top of the interior wall meets the ceiling.The ceiling symmetry dictated how large a perimeter and the resultant shape which in the final turned out to be a 14X25ft rectangle rather than a true square skyloop.My origional intention was to make this a CLOSEDloop horizontal skywire corner fed.for 10mtr.thru 20mtr and use a very short 5ft 5in. long un-balanced(flatline)feedline,a homemade 1/1 multiband rf choke,an antenna system tuner for multiband operation in conjunction with securing a 52 ohm resistive load for a proper termination of a lowpass filter. since i can not install any antenna outdoors at this apartment complex!my hopes were that it would radiate reasonably and as a closed Horiz.-loop at 25'(second floor)it radiates suprisingly well albeit at a rather high angle which i fully expected.on receive however it is as good as any antenna in the 1/wavelength class fully capable of receiving incoming lowangle waves as well.which admittedly surprised me.I considered an often overlooked technique of linear loading(physically lengthening the wire while maintaining the same footprint)to make this antenna a 2 wavelength loop at 3.5 so that i could take advantage of the multiband even harmonics properties and may try it later,i instead began to focus in on the problems associated with lowering the toa.while being confined to a fixed height!Here is where this gets very interesting.For my next experiment i decided to open the loop opposite the feedpoint and to my amazement something very interesting resulted.while a fellow ham assisted me at the rig to listen to what happened the instant i snipped/opened the loop and moved the ends of the wire an inch apart the existing signals that were weak suddenly intensified dramatically!The challenge is in trying to understand what actually happened.Before jumping to any conclusions, Lets first examine the affects that the "opening up of the loop at the opposite end of the feedpoint" had on the antenna, and on 20mtr.Upon 1st glance the feedpoint instantly moved,from corner to center.Why? because now the antenna may be veiwed as a doublet having two equal sides formed into an L-shape(more on the L-shape later) therefore two horizontal halves,furthermore the halves are long apx 44'ft.this length may be adding gain over and above the origional loop,attributable to the double extended zepp.since opening the loop resulted in instantaneous center feed it also instantly lengthened each half by an additional 5ft 5" because of the open wire that must be included in the total length of a doublet.hence the apx. 44ft a new total.Wow! thats alot of bang in a second!Now for another feasble additional feature that snipping the wire may have included, is in that it also may have lowered the toa as compared to the closed loop, by virtue of the fact that the antenna became a doublet,hence possibly lowering the toa since we can refer to many patterns cases that a doublet generally offers at the same aproximate height as my indoor antenna.But there is more...even though the antenna has changed from a loop to a doublet it may have also become a horizontal bi-square...hmmm.lets remember that even though i opened the loop it still maintains a loop shape,so what exactly do we have here?Remember i mentioned the two opposing L-shaped halves?Does this add or subtract gain,toa,pattern etc.?As i mentioned before a very interesting thing occured indeed!The question is just what is it?Incidently i am working dx with this antenna and low power on 20 meters.Maybe i will write more on this antenna as i further examine what it is doing on all the other bands.So in the spirit of experimentation..73's Bob Morris W5WSS