6M ground plane

[74IN]

I have googled it and I see pages that say the radials should be longer than the radiator.

I made a 2M ground plane and the radials were a 1/4 wave, like the vertical radiator. Worked great.

What's the real deal?

 

[W5LZ]

Which site says they should be longer? Sounds like they might be a little 'off', or maybe have some other reason for it. It can make a difference if those radials are on the ground or above the ground (elevated antenna). The radials used for a ground mounted vertical are not all that critical as far as their length is concerned, longer is better to some ridiculous degree. And since the current in those ground radials drops to zero before it ever gets to the end of them, they can be shorter than 'normal' too.
The radials used with an elevated ground plane antenna ought to be at least as long as the vertical element. That's typical for a 1/4 wave length antenna, doesn't matter what band it's for.
So the short answer would be that I don't know why 'they' would say that. The long answer is that 'they' may have had a reason for it.
- 'Doc

 

[74IN]

6 meter calculations

Them.

 

[W5LZ]

One thing I noticed about the calculations is that when finding a 1/2 wave, 492 is the 'magic' number being used. Nothing wrong with that as long as you remember that the diameter of that conductor isn't being taken into consideration. For average sized wire dipoles, the 'magic' number is much closer to 468 than to 492. That takes the diameter of average sized wire into consideration. That diameter thingy is commonly referred to as 'k', as in (492 x k)/F(in Mhz) = feet formula. Two ways of finding that 'k'. One is by doing the calculations referred to in the Amateur Hand Book Antenna section. The other way, as cited on that web site is by cutting an antenna till it's resonant at a particular frequency. Then, divide 492 by that frequency. Divide the experimental length frequency by the '492' length and you have 'k' for your resonant antenna's positioning, height, environment, etc, etc. The resulting 'magic' number will be less than 492 or 468, probably. That 468 number is really a good one cuz' it allows some fudge factor in the resulting lengths, a little extra, which is better than a little too short, sort of. A very rough 'ROT' (rule of thumb) is that for the lengths specified on that web site, if you multiply them b y 0.95, it's will result in a length closer to what you normally see for the length of a particular antenna. Hey, it ain't 'perfect', but it's close enough, sort of.
- 'Doc

That '492' number deals with the perfect, 'free-space' type antenna length. That '468' number deals with 'down-here-on-earth' type antenna lengths for 'average' sized wire antennas. Has to do with velocity factor, speeds of an electron in space and in air and in metals (it's a secret thingy, don't tell anybody!).
[The only B.S. in all of that is the last 7 words in parenthesizes.]

 

[Wire Weasel]

It generally shouldn't hurt anything to make GP radials a bit longer than the radiator, just don't make them any shorter. for a 1/4 wave Ground Plane anyway.

Good luck on the project!

 

[W5LZ]

Ditto the above.
- 'Doc

 

[Marconi]

74IN, try this article on radials.

http://www.comportco.com/~w5alt/antennas/