[Lf] LF antennas & ferrite rods

[Andre' Kesteloot]

Rik Strobbe wrote:

> At 16:12 3/07/00 +0100, G3XDV wrote:
> >Peter, G3LDO, had a worse result and we concluded that the type of ferrite
> >was critical (just try putting a broadcast type ferrite rod inside your
> >loading coil - it gets VERY hot). Possibly a rod made from SMPU cores would
> >work.
>
> I use a ferrite rod inside a part of the loading coil for fine-tuning my
> antenna on 136kHz. I did some testing to minimize losses (and avoid 'melt
> down').
> Conclusions were :
> - Material is (as expected) very important. Although all my rods are
> 'recycled' from old radio's they seem to be made of very different
> materials. When I put the rod into the big (5mH) loading coil and gave a 1
> min carrier with 35 Watt the rods got very warm to extemely hot (burnt my
> fingers on one). I used that method to find the rod (from my +/- 40
> quantity stock) that got least hot.
> - I coupled the rod very 'loosely' to the coil, just enough to get a 0.3mH
> variation in a 1mH coil (by sliding the rod up or down). This 0.3mH
> variation was enough to cover the 'steps' of the big 5mH coil that can be
> tuned in +/- 0.3mH steps (taps).
> With this setup the rod hardly warms up, even with 450W RF power.
>
> 73, Rik  ON7YD