Re: Antenna Length Calculation...was: "your mail"

[dan_masi@MENTORG.COM (Dan Masi)]

On May 13,  7:32am, Kurt Wesseling wrote:
> Subject: Re: Antenna Length Calculation...was: "your mail"
> Phil said:
> 
> > 
> > The ideal length is a 1/4 wavelength, minus a tad.  For VHF/FM
> > reception, say 
> > of a 93MHz station, the calculation (in metres) is something like:
> >  
> > Speed of light:         300,000,000 
> >                         -----------   /  4    (quarter wave)
> > Frequency:               93,000,000          
> > 
> > So the ideal length is around 80cm, or about 20.5 inches.  
> 
> Ok, now your getting into my area...8-]
> 
> Actually the most accurate, easiest way to figure the length of a
> VHF antenna is to use the following formula:
> 
> 2808/FmHz   ...that is divide 2808 by the frequency in megahertz. 
> This gives us the length in inches. (You metric guys can extrapolate)
> 
> So, with 93.0 mHz we get: 2808/93.0 =  30.1935483871
> 
> I think it will be safe to drop most of the digits after the 
> decimal...hehheh.  So, for 93.0 mHz we're talking about just over 30 
> inches.

Kurt, what was wrong with Phil's calculation?  He calculated,
correctly, that 1/4 wavelength of a 93Mhz signal, in free space,
is about 20 inches.  In real life, we'd slow down the propagation
speed a tad below 300Mm/s, but that would only serve to show the
effective wavelength as a bit *less* than 20". Where does the number
that you use, that gives us 30", come from?

Dan Masi, minister of propagation of non-Audi content
'96 A4Q