[Elecraft] 600 meters
Ron D'Eau Claire
ron at cobi.biz
Fri Jan 13 15:14:15 EST 2012
In the early 1990's, when CW was still the standard emergency mode at sea, a
radio officer on a ship in the Pacific was alerted by an SOS on 600 meters
(500 kHz). The ship located the signal on their radio direction finder and
headed in that direction. Sparks was unable to raise the ship but got off a
report to a GMDSS rescue and coordination center (part of the world-side
SOLAS - safety of life at sea - rescue system). The signal was coming from a
hand-cranked lifeboat radio. Hours passed as they tried to locate the source
of the signal, but the heading kept changing erratically. And then it
stopped.
Later they learned that the signal was indeed coming from a lifeboat radio.
It had been located and all hands rescued. The bizarre point was that the
lifeboat had been in the Mediterranean sea, not the Pacific Ocean. Some
strange antipodal propagation had produced phantom headings literally half a
world away.
I had the opportunity to interview the radio officer and read his logs when
visiting his ship to do an annual SOLAS inspection.
The lifeboat was probably using a kite antenna which, as noted by others, is
a pretty decent 600 meter antenna when flown to maximum height over salt
water. but the transmitter was running only a couple of watts output. The
signal may have followed the gray line path, but lower atmospheric
absorption typically remains very high for hours after sunset on those
frequencies.
It simply demonstrates that unexpected DX can be obtained on those
frequencies, although far less frequently that one expects at H.F. Indeed,
that might have been the second such surprise since Marconi heard the letter
"S" across the Atlantic at a much more challenging lower frequency using an
amazingly primitive coherer detector.
As for those experts who said a bumble bee cannot fly, all of the world's
scientists in 1890 agreed that radio waves could never travel farther than
line of sight. That's why a took an young Italian man messing about in his
attic with apparatus he constructed himself to prove otherwise. Marconi
often called himself the first Radio Amateur.
73, Ron AC7AC
-----Original Message-----
From: elecraft-bounces at mailman.qth.net
[mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Edward R. Cole
Sent: Friday, January 13, 2012 10:02 AM
To: Elecraft at mailman.qth.net
Subject: Re: [Elecraft] 600 meters
Mike Morrow, KK5F, wrote: "It is damnably difficult to radiate *much*
power on 600 meters unless
one has a lot of transmitter and real estate for antenna and ground."
"Most hams will be lucky to achieve a few milliwatts ERP from a few hundred
watts input power with small antennas not located over salt water."
Well I assume you are talking theory. I have been QRV for over a
year on 600m running 100w RF output to an inverted-L antenna (43ft
high x 122ft long) with large loading coil at the base. My
calculated (EasyNEC2) ERP = 4.15w (not mw). Granted that this is an
antenna efficiency of 0.8% so little RF is effectively radiated (most
is warming worms). I consider my soil as poor and use four radials
of 2-foot wide chicken wire laid on the ground surface. MY signal
has been detected 2800 miles away! QRO and renting a WWV site is not
needed! Some of our participants are radiating 20w ERP using 500w
amplifiers. BTW my 600m radio is my K3 or alternate Rx: SDR-IQ.
BTW I regularly check into the Elecraft 20m-SSB Net with 16w from my
K3/10, with little problem. Again, QRO is overrated. Maybe in a QRM
loaded 20m contest but this does not exist on 600m. Just a handful
of experimenters and enthusiasts finding out what can be done with ERP<20w.
Actually more than you would guess. Out to 300-km propagation is
100% all the time using ground wave. I made a series of GW tests in
summer of 2010 running 4w ERP with +35 dB SNR ( S6-S7) at 100-miles
at my two receiving partners. I wish our station in North Pole (AK)
had been active (300-mi) to gather info at that range.
In the winter 600m acts somewhat like 160m with lengthening DX over
thousands of miles. I have copied a station in Buffalo, NY at about
4000 miles from me, and several instances of copying Vancouver, BC
and Oregon (1300-2000 miles). The biggest limitation is static noise
in the lower-48. It doesn't exist much up here in Alaska.
So, yes, full-size antennas are huge, but a typical 160m antenna, if
loaded, will work pretty good!
BTW I've heard that theoretically bumblebees cannot fly! ;-)
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