TopBand: Need info on vertical with top loading

[George.Guerin@kellogg.com (George Guerin)]

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     Hi Leon:
     
     What you describe below would be resonant on 80 meters, over a decent 
     radial system.  Since it is top loaded, the impedance at resonance 
     will be less than 36 ohms, maybe 30 ohms with little top loading.
     
     ON4UN's Low Band DXing books show his linear loading for a taller 
     vertical.  I guess you could put up a "hairpin" full height and come 
     close to resonance on 160.  Linear loading is typically 70 percent 
     efficient if done at the feed point.  However, the impedance will be 
     very low at the feed point.  Some sort of matching network will be 
     needed to get to 50 ohms.
     
     Another approach:  make an inverted L out of it.  Make a trap for 80 
     meters, using coil stock, or wire wound on a piece of UV resistant PVC 
     conduit or pipe.  2-1/2 inch PVC is actually 2-7/8 OD, which is a good 
     size.  Use two door knob ceramic capacitors, totalling 150 to 200 pfd 
     to make the trap resonant at about 3525 Khz.  Put the trap about 20 
     feet out from the top of the mast to get 80 meter resonance and then 
     extend the wire out for 160 resonance.  The trap will give you some 
     inductive loading so you will be about 15 feet shorter than a total 
     length of 128 feet from feed point to end insulator beyond the trap.  
     The antenna probably needs a 9:4 UnUn to get the impedance on 160 up 
     close to 50 ohms.
     
     George, K8GG.
     
     
______________________________ Reply Separator _________________________________
Subject: TopBand: Need info on vertical with top loading
Author:  Leon <leon0@ibm.net> at BC_INTERNET 
To: <topband@contesting.com>
Date:    11/4/97 1:01 PM
     
     
Hello all,
     
Thanks for reading this.
     
I want to put up a 40-50 foot aluminum tower with about 20 feet of 
     
top loading for 80 and 160 meters. I may also linear load it for 160.
     
I was interested in any comments anyone may have or how they may have
     
went about this.
     
Thank you,
     
Leon WA7ZXZ
     
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