On 9/14/2010 5:09 PM, Owen Duffy wrote:
"Ralph wrote in
m:

...
That is what I am using on a home built version. Using a 4:1 voltage
balun at the feedpoint and the ferrite bead type about 20 feet down
from the feedpoint.

The ferrite choke is doing something as it gets warm while running
around about 1 KW to the antenna. Doesn't heat up when going into a
dummy load.

I am not surprised at your results with a dummy load. If it is a well
screened unbalanced dummy load, you should expect zero dissipation in the
balun cores.

The fact the balun cores are heating in the antenna scenario indicates
there is some common mode current. You probably have no idea of the
current.

Something to keep in mind is that the average power of uncomressed voice
SSB is about 3% of PEP, so if your 1kW was uncompressed voice SSB, the
average transmitter power might be more like 30W, or half that in a 50:50
over scenario over the long term.

Another thing is the ferrite toroids heat and cool very slowly, so the
operating temperature might still be rising half an hour after the
transmitter is applied (so long as you haven't exceeded their Curie
temperature).

It would not surprise me if the common mode choke consumes a significant
portion of transmitter power on some bands, the portion will depend a lot
on your own scenario.

Owen

Even worse than that! A lot will only consider the loss in the
transmitted signal of such an antenna, perhaps even call it "trivial."
However, the received signal will suffer from exactly the same losses
.... while even losing 500 watts of a 1KW signal can be considered
"trivial", losing 50% of ones received signal is NOT!

Regards,
JS