Use line of coax appr. 2 m long for 400 Mhz. Power it up from Generator
(CV). Attach quarter wave radiator on another end (bare piece of wire).

You expect to have power running back along the outside of the coax shield.

How to see it - make a detector: pick up coil - several turns of wire small
radius. Load it on diode (LED works too). Measure voltage across the diode.

when you move detector along the coax, you will see nulls and maximums,
approximately half wave length from each other (may vary considerably
depending on your setup.)

now add ferrite choke at the antenna end of the cable. Observe change of
amplitudes you see with detector. Add more ferrite.Observe how efficiency of
your choke improves when it's length increases.

....
it is all fine up to here - you observed operation of the ferrite choke. Is
it a good balun - depends. Unlike coaxial sleeve the ferrite choke absorbs
the energy - it is not sending it back to the antenna.

Andrey





"MikeN" wrote in message
...
How could one measure the effectiveness of a ferrite bead used to
decouple a feedline from a driven element at 70cms, with simple
equipment which could be built by a homebrewer, and what would that
simple equipment be.

Thanks MikeN