[TowerTalk] Even more: Topband: New Antenna

[DAVID CUTHBERT]

  ----- Original Message ----- 
  From: DAVID CUTHBERT<mailto:DAVIDNNAN at MSN.COM> 
  To: towertalk at contesting.com<mailto:towertalk at contesting.com> ; topband at contesting.com<mailto:topband at contesting.com> ; WarrenWolff at aol.com<mailto:WarrenWolff at aol.com> 
  Sent: Sunday, December 26, 2004 7:38 PM
  Subject: More: Topband: New Antenna


   
  Warren,

  I thought I had better really simulate the flagpole rather than just dismiss it out of hand. Here are some possibilities:

  1) wire from the top of 35' flag pole to the tower, at the 35' level. Rr = 7 ohms
  2) wire from the top of the 35' pole towards the top of the tower. Rr = 16 ohms 
  3) wire from the top of the 70' tower (not attached to the tower) towards the top of the 35' pole. Rr = 16 ohms
  4) wire connected to the top of the 70' tower towards the top of the 35' pole. Rr = 17 ohms
  5) tower feed. 16 ohms. 
  6) top load the 70' tower with a coil and a top hat or spike. Rr = 25 ohms. The only design that does not need the 35' pole. 

  Number 1 looks bad. Scratch that one. Numbers 2-5 all look good from a performance standpoint. Number 2 looks to be the simplest to implement. This can be fed directly with 50 ohm coax and tweaked with a good antenna tuner at the shack. This is the one I would seriously consider. Number 6 has the highest performance IF your ground system is not very good. You get 9 ohms more Rr at the expense of a few ohms of top loading coil loss. This one needs shunt feeding of the tower and is a lot more complicated to get going than number 2. If your ground system is good I would not bother with the added complexity of this one. 

  These sims are subject to having better inputs (dimensions, ground, radials, etc.) but I believe them to be good for comparison of the different designs. None of these, except for number 6,  requires loading coils. All of the rest are adjusted to resonance by the length of the horizontal wire. 

  BTW, I use a 38' top loaded vertical. It is all I can fit in my antenna unfriendly neighborhood and small back yard. 


       Dave  WX7G


    ----- Original Message ----- 
    From: WarrenWolff at aol.com<mailto:WarrenWolff at aol.com> 
    To: towertalk at contesting.com<mailto:towertalk at contesting.com> ; topband at contesting.com<mailto:topband at contesting.com> 
    Sent: Sunday, December 26, 2004 12:29 PM
    Subject: Topband: New Antenna


    Greetings,
     
    I have a question about choices on 160 meters.
     
    I expect to have a new home at Lake Havasu City next  summer.
    I will have a 60/70 foot fixed tower topped by a couple of  OptiBeams
    (16-4 and a 4-40).
     
    About 100 feet away, I expect to have a 30/35 foot flag  pole.
     
    What is my best way to get on 160 with this arrangement?   A couple
    of ideas come to mind.
     
         1)   Shunt feed the  tower
    2)   Use a wire between the top of  the tower and the top of  the
    flagpole  to use as top loading for vertical wire in the  center
    of  it.
    3)   Extend an arm out from the top of  the tower, say around  6-8
    feet and  drop some kind of vertical element to be base-fed.
     
    Advice is needed; please don’t say I am nuts.
     

    Warren; W5KKW
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