I am surprized no one caught the error! I even gave you a clue in the sentence after the computations.
the formula for 1/4 WL = Vf * 248/Fmhz, not Vf * 492/Fmhz So if you make your 144-MHz phasing line 27 inches of RG-11, it WILL be too long!
It is true that manufacturing variations in Vf occur from roll to roll of coax. If you can measure it, this is prefferable to assuming the mfr's data. But, using the published numbers is fine if you do not have special equipment.
73, Ed - KL7UW
At 09:59 PM 9/19/2008, Edward Cole wrote:
You are making too much of a big deal out of this. Velocity factor is published by coax manufacturers so you do not need instruments to get close. 1/4 WL = Vf * 492/Fmhz in feet 1/4 WL (RG-213) = 0.66 * 492/144 = 2.25 feet or 27-inches
If you are off 5% it will not destroy the circularity. Most hams get it "close enough". Of course if you are off by a quarter wavelength or more it will matter (20-inches at 144-MHz). GL
73, Ed - KL7UW BP40iq, 6m - 3cm 144-EME: FT-847, mgf-1801, 4x-xp20, 185w http://www.kl7uw.com AK VHF-Up Group NA Rep. for DUBUS: dubususa@hotmail.com
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