[time-nuts] 60 KHz Receiver
jimlux at earthlink.net
Thu Oct 7 14:26:04 UTC 2010
Bob Camp wrote:
> The one thing that an alternator system had available was *power*. They are fairly efficient and you put lots of horsepower into them. Numbers in the 100's of KW come to mind....
> What we're talking about here is more or less a page from the history of radio in the early 1900's. People that were used to the requirements of a VLF system simply didn't believe that a few watts would get very far at "short wave". It took a bunch of crazies to prove them wrong ...
So even if your antenna system were 1% efficient (which would be doing
well) you could still radiate kilowatts.
There was an article in IEEE Proceedings back in the 70s(?) describing
the VLF comm system and what was interesting is that the propagation
losses were quite low (150dB-160dB, I think), the background noise at
the frequency was low, so you didn't need huge radiated powers to make
the system work. I seem to recall that the big antenna near the Great
Lakes radiated 1 watt, but required something like a megawatt into the
antenna ( a series of buried wires) to get that radiated power.
In the early days of wireless, ships had 500 or 1000 Watt transmitters,
rated by power input to the system. Hence the US amateur radio limit of
1kW DC power to the final stage, so interference was limited. The
amateurs were limited, the ships have a minimum power requirement.
I think a lot of the astounding performance (to folks at the time) on
200m and down wasn't so much because propagation is better, but because
it's easier to radiate the power efficiently when the frequency goes up.
This was back in the days 20s when the long haul RF links were running
at 10s of kHz
I was surprised to see how late it was before the first *wired*
transatlantic phone call was made: 1956 ($12/3 minutes, 36 lines
available). the first Telstar call wasn't that much later in 1962.
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