Re: [TowerTalk] real world formula for the length of a quarter wave transmission line

[Jim Lux <jimlux@earthlink.net>]

On 2/13/13 11:39 AM, n2mm@comcast.net wrote:
> Help,
>
>
>
> I lost my antenna handbook. Does anyone know the formula that is
> fairly accurate for a 75ohm quarter wave tranformer for my 80m quad.
> is it 234xVF     or 246 x VF
3e8 m/sec free space speed of light

300m/microsecond

80m is 3.75 MHz

80meters*VF gives you one wavelength

that's 80*3.28 ft = 262.4 ft

so a 1/4 wavelength is going to be 262.4/4*VF ft or 64.6*VF feet
for 3.5 MHz -> lambda = 300/3.5 = 85.7 meters = 281 ft
for 4.0 MHz -> lambda = 300/4 = 75 meters = 246 ft

So, for a top of 75meters 1/4 wave, it would be 246*VF/4 or 61.5*VF
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