The short answer is no. One of the best readily-available ferrites for
VHF use is Fair-Rite type 61. At 6 meters, one core of this material
will look like a resistor of a few ohms in parallel with an inductor
whose reactance is also a few ohms. That combination won't do what
you're asking.

Even if you locate a better material, you'll still only have a few ohms
of reactance for a single core at that frequency, and the Q is likely to
still be not very good. It'll be a long way from making a trap, which is
what you're trying to do.

Roy Lewallen, W7EL

wrote:
Hi Group,

Let's say I have a 15 meter dipole. If I were to take a ferrite core
and place a core along the dipole for the lenght of 6 meters, having
two cores on either side.

The question is would this antenna now work as a dipole on 6 meters but
not on 15 unless the reactance of the core was low at 21 MHz?

Does the core act as a RF block but not as a inductance with a
reactance at 15meters?

If it is a inductive reactance, then reducting the lenght of the dipole
would bring down swr on 15m.

I have seen the ferrite emi cores which clamp around the wire, would
these work for 100 watts?

If I had a way to move the cores along the dipole, I could create a
multiband antenna, true?

I am sure there are better ways to do such, aka trap dipole but I like
to give this some thought.

De KJ4UO