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Old 08-10-2011, 08:52 PM
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Question Building 2.4Ghz Omni antenna, have questions

Hi

I recently became interested in building Onmi antennas and have decided on building the antenna from the guide you can find on google searching "Easy Homemade 2.4 Ghz Omni Antenna"

I however have chosen a better quality cable (LMR-400, Solid Core). I have determined my segment measurements to be 5.219655660 (52.2mm) each. I am having trouble on some things and need answers to some questions.


Per the instructions from a different antenna I found searching google for "Omni-Gain Vertical Collinear for VHF and UHF", i found one said to bend the last center conductor over and solder to Shielding.


1.) Is there any specific length this center wire should be before folding over?


2.) Is it required to have an N connectors or can I have the fly lead ran without having to cut away more? i.e. Last Segment runs direcly to Router, but with adjustable Toroids or De-coupler to get final 1/4 Wavelength?

3.) I bought LMR-400.... Not a math wiz, did I calculate correctly 52.2mm per segment correctly? (the velocity (%) says 85) per rfparts dot com

4.) Will the spacing between segments remain the same as those mention on site at the beginning of this post?

His calculations
37 +6 +6 +1 = 50mm of cable for each sector"

Mine corrected
52.2 +6 +6 +1 = 65.2mm of cable for each sector"

5.) With the LMR-400 will my whip length change from 31mm as per the same guide as mentioned in question in 1st paragraph


6.) How do I calculate a 1/4 wave?

Again search google for "Omni-Gain Vertical Collinear for VHF and UHF" (1st result) Step #7 simply says to use 1/2 of the 1/2 wavelength.

where This site paragraph ones site says The 1/4 wave element is not adjusted by the Velocity factor...

Confused.....


Thanks for any guidance!
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Old 08-11-2011, 12:18 AM
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wavelength in air, measured in meters = 300/frequency in mHz

1/4 wavelength in air = wavelength / 4

1/4 wavelength in coax = ( wavelength / 4 ) * Velocity Factor
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