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Author Topic: 22' Vertical or Screwdriver Antenna  (Read 957 times)
KB3FFH
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Posts: 161




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« on: July 26, 2012, 07:31:13 AM »

I am deciding between a 22' vertical antenna with remote tuner at base of antenna or a screwdriver antenna. Eighter would be mounted on the roof of my house with wire radials laying on roof. I want 10-80 or 160 meters. Is one better than the other. Thanks Bill
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WX7G
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Posts: 5973




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« Reply #1 on: July 26, 2012, 07:50:10 AM »

Neglecting tuner or loading coil losses the longer monopole will have higher radiation efficiency.

And an antenna with top loading will have about 3 times the radiation resistance as base loading. I think for your situation a Hustler 5BTV with a remote tuner at the base will provide the best performance and it is 21' tall. On 10, 15, 20 and 40 meters the tuner will do little. On 80 meters the 5BTV is top loaded and has a 3:1 VSWR bandwidth of about 70 kHz. The tuner will extend this over the entire band. On 12, 17, and 30 meters the tuner will do the job. For 80 meters you will want to adjust the "resonator" whip to resonance at the center the part of the band you like to operate.

For radials two resonant radials per band run opposite one another is optimum. But by decoupling the remote tuner and control cable non-resonant radials may carry more current than the tuner coax/control cable, which is a good goal. If the tuner has no control cable - the control and power is via the coax - I would install an MFJ-915 isolator at the antenna. Make sure the antenna has no other connection to earth ground.

If the tuner has a control cable both the cable and the coax should be routed through the same ferrite toroid cores. 
   
Several Fair-Rite 5943003801   Cores (Mouser has them in stock) will work. Wrap several turns of the cables through several cores. Do not use an "ugly balun" because they are narrow band and hi-Q. For a good balun or choke we want it to present a high, resistive impedance over a wide frequency range.
5943003801
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W8JX
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« Reply #2 on: July 26, 2012, 08:09:41 AM »


And an antenna with top loading will have about 3 times the radiation resistance as base loading. I think for your situation a Hustler 5BTV with a remote tuner at the base will provide the best performance and it is 21' tall. On 10, 15, 20 and 40 meters the tuner will do little. On 80 meters the 5BTV is top loaded and has a 3:1 VSWR bandwidth of about 70 kHz. The tuner will extend this over the entire band. On 12, 17, and 30 meters the tuner will do the job. For 80 meters you will want to adjust the "resonator" whip to resonance at the center the part of the band you like to operate.


I have used a ground mounted 5BTV for nearly 20 years and NEVER needed a tuner on 40, 20, 15 or 10 as SWR is well below 2 to 1. On 80 I have a bandwidth of about 90khz at 2 to 1 or less. SWR does climb rapidly beyond this so a tuner would be needed if you want to cover a bigger area of 80.
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N4UM
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Posts: 468




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« Reply #3 on: July 26, 2012, 02:41:27 PM »

W8JX  re: 5-BTV " On 80 I have a bandwidth of about 90khz at 2 to 1 or less. SWR does climb rapidly beyond this so a tuner would be needed if you want to cover a bigger area of 80"

That seems awfully broad to me for a 5-BTV.  I would suspect your ground losses are probably fairly high which might account for the "apparent" broadbandness."
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