We have 3 ways to construct a choke (ie a 1:1 balun).
1. "Ugly Balun" coax wrapped around PVC, etc.
2. A Guanella Balun which is Bifolar wire wrapped around a torrid
3. Simple Choke that is just a bunch of ferrite beads slipped over coax.
What is common in all of these approaches is that the coax is made into a coil. With
enough impedance in series with the outer shield, the common mode currents will
be greatly reduced.
The only difference among them is how this is done: #1 and #2 use multiple turns to
increase the inductance. (#2 can use coax rather than a bifiliar winding of wire.)
#2 and #3 use ferrite to increase the impedance per turn. In all cases the choke
must have sufficient impedance across the operating frequency range to be effective.
Usually the lowest effective frequency is determined by the inductance, and the high
end by self-resonances.
Chokes using ferrite tend to have a wider operating frequency range than those on
an air core, but the ferrite material must be chosen to give enough impedance without
saturating at full output power. Using ferrite and/or multiple turns gives more inductance.
G3TXQ ha taken actual measurements on many different designs, and the results and
recommendations are available on his web site: http://www.karinya.net/g3txq/chokes/
Further reading on how baluns work and why a choke balun really is a balun rather than
an unun in the classic article by W7EL: http://www.eznec.com/Amateur/Articles/Baluns.pdf
There are other types of 1 : 1 baluns as well, though many are more common at VHF/UHF.