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Author Topic: Cutting Radial length  (Read 810 times)
N6SBN
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« on: April 08, 2013, 02:35:16 PM »


  Antenna  S9-V31.   The vertical wire and radials are attached to an UNUN.   50' of Coax running from the UNUN to the Radio.

  I have 12" of wire running from my UNUN to the radial plate.   Now, I want to cut radials at 8 and 11'.   Do I cut them 7' and 10' lengths, considering the 1' of wire running from the UNUN to the plate?

Thanks in advance.  Craig
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W8JX
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« Reply #1 on: April 08, 2013, 02:50:43 PM »

Why pick 8 and 11 feet? It is a non resonant antenna so radial length is not critical when elevated and does not really matter at all when they are in the dirt.
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N6SBN
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« Reply #2 on: April 08, 2013, 03:05:33 PM »

  I read about people cutting the radial at specific lengths.  My Vertical is up on the roof.  The radials are tapered downward.
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W8JX
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« Reply #3 on: April 08, 2013, 03:15:54 PM »

Length is critical for resonant antennas but with a non resonant one like this fed with a unun and a tuner it is not. 
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N6SBN
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« Reply #4 on: April 08, 2013, 03:18:50 PM »

I plan to put an SGC AT at the Vertical's feed point.  Would that make any difference?
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W8JX
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« Reply #5 on: April 08, 2013, 04:00:13 PM »

Not really other than it will reduce feed line losses that can be present from high coax SWR to a tuner in shack. General you want to use as many radials as practical
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WB6BYU
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« Reply #6 on: April 08, 2013, 04:43:46 PM »

For elevated radials you generally would want them close to quarter wave
resonance, even if not needed for impedance matching.  They help to reduce
common mode current that way.

Unfortunately it isn't a simple matter of subtracting the length of the connecting
wire from the radial length.  I'd have to model it to see, but my guess is that
reducing the radial length by about half the connecting wire length is probably
closer than using the full length.  That would probably get you close enough,
anyway.
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W8JX
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« Reply #7 on: April 08, 2013, 06:14:54 PM »

For elevated radials you generally would want them close to quarter wave
resonance, even if not needed for impedance matching.  They help to reduce
common mode current that way.

Yes normally but this is not really needed nor practical for a non resonant vertical such as this. These types of antennas kinda follows different rules.
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K2OWK
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« Reply #8 on: April 08, 2013, 09:40:27 PM »

I have a S9 31 foot with the same setup. I have radials buried about 2" below the ground. They vary in length between 26' (most of them) and 3' (just a few). The antenna operates first class with no problems. My coax is RG8X about 50' and I can tune the bands 80 thru 6 meters. I am using an MFG Auto Tuner Extender (MFJ-914) for most bands and an MFJ-949E for the rest. The radio is a Yaesu FT-450AT. I have the UNUN mounted on the radial plate with about 4" of braid attaching it to the plate.

73s

K2OWK
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