[TowerTalk] Re: 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> ; DAVID CUTHBERT<mailto:DAVIDNNAN at MSN.COM> 
  Sent: Sunday, December 26, 2004 7:43 PM
  Subject: Even more: Topband: New Antenna


   

    ----- 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 
    3A) wire from the top of the 70' tower (not attached to the tower) towards the top of the 35' pole. Rr = 16 ohms. Fed at the base.
    3B) wire from the top of the 70' tower (not attached to the tower) towards the top of the 35' pole. Rr = 16 ohms. Feed at the 70' level. About 40 ohms.
    4) wire connected to the top of the 70' tower towards the top of the 35' pole. Rr = 17 ohms. Shunt feed.
    5) tower feed. Rr = 16 ohms. Shunt feed with a wire to the top as you proposed.
    6) top load the 70' tower with a coil and a top hat or spike. Rr = 25 ohms. Feed with coax at the base of the spike/top hat. It can be thought of as a vertical with elevated feed or an Isotron.  

    Number 1 looks bad. Scratch that one. Numbers 2-6 all look good from a performance standpoint. Numbers 2, 3A, 3B, 5, and 6 are interesting.  Number 6 can be matched with a 90 degree, 75 ohm coax, as the input R is around 140 ohms.  Number 6 has the highest performance and might be the way to go if your ground system is not very good. You get 9 ohms more Rr at the expense of a couple ohms of top loading coil loss. For ease of getting it to work I would chose 2, 3A, or 3B. 

    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. 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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