Ideal Antenna Length (In Theory)

SSTJ

SSTJ

———
Lifetime Supporting Member
Joined
Aug 24, 2019
Messages
3,351
Location
South Carolina
So I've been reading about antennas. It seems that the most common length for a dipole antenna is 1/2 wavelength, with each 'pole' being 1/4 wavelength. But on mobile rigs we only have one 'pole', and the frame acts as the counterpoise in place of a lower, second 'pole'.

So for our 'monopole' antennas, what's the ideal length? Is it still 1/4 wavelength, or something else?
 
Antenna design is really fun, especially the signal patterns. There isn't best, just best for what you want. You might consider learning how to read antenna signal plots so you could answer these questions for yourself. If you have questions about what the plots mean just ask.
 
  • Like
Reactions: SSTJ
Simple answer:

In addition to being relatively short, a 1/2 wave antenna typically does not require a ground plane, which is the primary reason 1/2 wave antennas are so popular in jeep mobile installations,

A 5/8 wave antenna provides additional gain at relatively low angles without a huge increase in length, which also makes them a popular choice. However a ground plane is required with a 5/8 wave antenna.

1/4 wave antennas, while very short and unobtrusive, also require ground planes to perform properly.
 
  • Like
Reactions: Blondie70
Mr. Bills said:
Simple answer:

In addition to being relatively short, a 1/2 wave antenna typically does not require a ground plane, which is the primary reason 1/2 wave antennas are so popular in jeep mobile installations,

A 5/8 wave antenna provides additional gain at relatively low angles without a huge increase in length, which also makes them a popular choice. However a ground plane is required with a 5/8 wave antenna.

1/4 wave antennas, while very short and unobtrusive, also require ground planes to perform properly.
Click to expand...

Interesting, thanks! And just to clarify, on your first point about 1/2 wave antennas. Am I right in understanding that when you refer to 1/2 wave antennas for Jeeps, you're still talking about a 1/4 wave monopole with the frame as counterpoise?
 
SSTJ said:
@Mr. Bills and @pagrey

So, if the wavelength of a CB radio is around 40', why do I see 4' Firestik antennas advertized as "5/8"? Wouldn't 4' be more like 1/10?
Click to expand...

The antenna is wrapped around the stick.

818gNeWgoML._AC_SY879_.jpg
 
I don't think Wikipedia is the go-to or anything like that, just the information is there and the links tend to be pretty stable over time.
 
Top Bottom
Back