Hello Roy -

I will try your suggestions when I build a more powerful power amp.

As the modulation is AM with known 25% there is a interesting measurement
methode possible:
Ramp the amplifier from low to high power and make a curve of the AM
modulation depth at the receiver or just with a measurement coil at the
transmitter ferrite rod. It should show a saturation if the ferrite goes in
saturation. I will try this.
There is an open question what a time constant the ferrite will have if it
goes into saturation or out of it. And if this is very different if iron
powder is used.

- Henry


"Roy Lewallen" schrieb im Newsbeitrag
...
Henry Kiefer wrote:
. . .
If you talk about explosion: What is the power level you mean?
Currently I have a ferrite rod of 9mm diameter and 50mm length, driven
by
40mA against 2Vpp.
Do you think it is impossible to pump maybe 5watts into the rod?

Dunno. If it had to dissipate most of the 5 watts (which is likely), it
would get as hot as a resistor that size dissipating the same power, and
that would be pretty hot. Just how hot depends on how well insulated it
is, how good the air flow is around it, and how much heat is conducted
away through the wires or any other physical connection. The first thing
I'd check would be the Curie temperature of the ferrite. If you reach
that temperature, the material will lose its magnetic properties, so the
antenna impedance will abruptly and dramatically change. At some higher
temperature, the ferrite will fracture, maybe violently.

If that gets to be a problem, a lower loss ferrite might be necessary.
That usually means lower initial permeability, and probably a lower Q
inductor. You'll have to determine what the optimum trade would be.

Shouldn't be any trick to feed some power to one and watch its
temperature with a thermocouple.

Roy Lewallen, W7EL