On Aug 6, 9:23 pm, Roy Lewallen wrote:
Sal M. Onella wrote:
. . .
What's the record for max BCB power?

Dunno, but some of the SW BC stations sure are impressive. I had the
opportunity to see the Deutsche Welle facility at Wertachtal, Germany a
couple of years ago. It has, I believe, 12 ea. 500 kW transmitters, and
the antenna consists of several miles of curtain array with reflector
grids on both sides for reversibility, arranged in a pattern of three
long radials from a central building. It can also be electronically
steered to some degree. Modulation could be heard at about a half mile
from the antenna, apparently from vibration of some of the antenna feed
components. That facility leases time to many other international
broadcasters.

Roy Lewallen, W7EL

No wonder, then, that they can put a 0dBm signal into a decent ham
antenna on 7MHz on the US East Coast. Still, I'm always in awe of the
efficiency of propagation through the air, bouncing between the
ionosphere and the earth/oceans. On the same roughly 5000 km path
through a piece of dry air insulated minimum loss copper coax 1/3
meter diameter (a bit over a foot diameter; about 5 millidB/100feet
loss@7MHz), fed 6 megawatts at the input, you get an undetectable
signal out the other end, over 800dB loss yielding an output less than
-700dBm. [6 megawatts at 76 ohms is 21kV rms, so a line that large
should handle the voltage, but at the transmitter end, such a line
would dissipate about 60 watts per foot.]

Cheers,
Tom