Wavelength forumlas

[MarkEagleUSA]

There seems to be 2 sets of factors used to determine antenna lengths at various wavelengths. The first set is based on the fact that radio waves travel at 984 million feet per second (984/Mhz). The second set is about 5% less (936/mHz). Can someone explain under which conditions which set of factors are used and why they're different?

Wave	Set A	Set B
------	------	------
Full	984	936  (<factor>/mHz=length in feet)
7/8	861	819
3/4	738	702
5/8	615	585
1/2	492	468
3/8	369	351
1/4	246	234
1/8	123	117

 

[kf4lne]

The first set, based on 984/freq is the theoretical formula, it is only a good reference point, the set that is 5% different, 936/freq is the actual formula used for building antennas, it takes into account things like velocity factor and end effect and all kinds of other technical details, so when building an antenna you can use either formula, but the 936/freq based formulas will be better to use for reality antennas wheras the 984/freq formulas are for determining wavelength in freespace with nothing else around

 

[MarkEagleUSA]

Thanks... someday I might actually understand some of this stuff.

 

[kf4lne]

For now just stick with the 936/freq formula set and when building antennas shoot for the middle of the band you want to scan, so if you want to scan all of low band, from 30-54MHz, cut an antenna for 42MHz