Frequency formula

[HogDriver]

Two things, first, I’ve heard a formula that you take 468 and divide by the frequency in MHz and you’ll get the length in feet for a half-wave antenna. Second, by doing that, I get 1.09 ft. for 855 MHz. Is a full wave antenna more efficient than a half wave or does it matter?

 

[buddrousa]

The answer is yes but it would only be 100% at 1 frequency and will fall off going each direction not much but a little.

 

[Ubbe]

A 1/4 wave will have the appropriate impedance. Half or full wave needs loading coil for impedance match and probably groundplanes if the direction shouldn't point up in the sky. Dipole half wave are ok as it consists of two 1/4 waves.

The radiowave travels 300 000 000 meters per second so in metric you divide 300 by the frequency in MHz to get a full wave. 855Mhz are 35cm which are 1.15ft for a full wave. Then the material of the antenna where the radiowave travels over will delay the signal by 5% for most metals so the antenna for a full wave are 1.09ft. The formula you use are correct for getting a full wave.

/Ubbe

 

[vagrant]

Whatever the calculation result, make it a little longer and then cut down/tune to size. For example, a recent UHF antenna I was cutting and tuning in the amateur 70cm band was trimmed one mm at a time on the sections and it made a difference on the analyzer each time. I was fine tuning it for a specific frequency and not a range, but you get the idea for an antenna at 800 MHz.

 

[jhooten]

468 takes into account the velocity of propagation of the radio wave in other than a vacuum. It is a starting point for antenna construction. 492 is the number for a halfwave in free space.