[600MRG] Radio Amateur’s Sub-9 kHz VLF Signal Detected Across the Atlantic [W4DEX - WD2XSH/10]
Ralph Wallio, W0RPK
W0RPK at netins.net
Sat Jun 7 04:15:33 CDT 2014
http://www.arrl.org/news/radio-amateur-s-sub-9-khz-vlf-signal-detected-across-the-atlantic
Radio Amateur’s Sub-9 kHz VLF Signal Detected Across the Atlantic
06/06/2014
How low can you go? A signal on 8.971 kHz has spanned the Atlantic, from
North Carolina to the UK. Running on the order of 150 µW effective
radiated power, very low frequency (VLF) experimenter Dex McIntyre,
W4DEX, transmitted signals on June 2 and 3 that were detected by Paul
Nicholson, an SWL in the UK. Earlier this year, Nicholson detected
McIntyre's WH2XBA/4 Experimental Service VLF signal on 29.501 kHz.
McIntyre needed no FCC license to transmit on 8.971 kHz, since the
Commission has not designated any allocations below 9 kHz — dubbed “the
Dreamers’ Band.”
“I’ll probably make more transmissions on 8.9 kHz when there is no
chance of thunderstorms,” McIntyre told ARRL this week. “Then, maybe
sliding down in frequency to see how low I can go for Paul to detect the
signal.”
Right now, McIntyre said his priority is to complete a transverter for
the other end of the spectrum — 5.7 GHz. He’s also working on a second
24 GHz system as a loaner, “so I’ll have someone to work,” he noted.
“Sure is lonely here above UHF.”
Nicholson used sophisticated digital signal processing (DSP) software to
detect McIntyre’s transmission. The distance was approximately 6194 km
(approximately 3840 mi). Nicholson was able to detect the VLF signal
during both daylight and nighttime paths.
On June 1 and into June 2, McIntyre transmitted a steady, GPS-locked
carrier at 8.971.000 kHz. Between 0000 and 0600 UTC, Nicholson measured
a carrier at that frequency in Todmorden, UK. He combined the electrical
and magnetic field receiver outputs to produce a unidirectional antenna
response.
“This brought the signal up to a significant level,” Nicholson reported.
“The signal bearing was roughly west. W4DEX is bearing 285° from here.
The S/N is max on a bearing of 315°, which puts the prevailing
southwesterly background nearer to the side of the antenna response.
This gave the signal a respectable 12.5 dB S/N in a 46 µHz bandwidth.”
Nicholson said McIntyre’s carrier also was visible during a daylight
path in a 23 µHz bandwidth.
Just to confirm that Nicholson was actually detecting McIntyre’s signal,
the two experimenters conducted a blind confirmation test. McIntyre
changed his transmit frequency slightly, and Nicholson was also able to
detect that signal at 8.971.100 kHz at the same strength. An e-mail
response from McIntyre confirmed 8.971.1 kHz as the new frequency.
Is a two-way sub-9 kHz contact in the offing? “A two-way, transatlantic
contact would be a hundred times more amazing than just a simple signal
detection,” McIntyre said. “I seriously doubt I will ever have that
receive capability. But not long ago I seriously doubted I would be the
first to receive a transatlantic or New Zealand 137 kHz transmission.
Going down in frequency has been as much fun as going higher. It’s all RF.”
McIntyre expressed his appreciation to Nicholson, “who was convinced
this could be done with so little radiated power and for his continuous
prodding to give it a try.” He also credited Nicholson’s “amazing
weak-signal software.
McIntyre’s transmitter consisted of a Hewlett Packard HP 3586B selective
level meter with tracking generator. The low-level generator output is
amplified by a Wandel & Golterman A-160 level regulator, which feeds a
Hafler P3000 stereo audio amplifier, which has been bridge connected for
mono output. In this configuration, the P3000 is capable of putting out
400 W of audio into an 8 W load. McIntyre said the same generator and
amplifier have been used on 137, 74, and 29 kHz experiments.
His antenna is essentially the same one he uses for 160 meters and for
other LF experiments. For this experiment, however, it was equipped with
a gigantic base-loading coil, which contains nearly a mile of wire. “The
vertical wire is spaced 1.5 meters from the tower, hanging from an
insulator 29 meters above ground,” McIntyre explained. “Top hat consists
of about 170 meters of #18 Copperweld. Most of the top hat wires run
about 7 to 20 meters over the top of a combination of oak and pine
trees. Total antenna capacitance is close to 1200 pF.”
McIntyre also thanked Jay Rusgrove, W1VD, and John Andrews, W1TAG, for
their technical advice, Markus Vester, DF6NM, for technical advice “and
additional prodding,” Mal Hamilton, G3KEV, for coming up with the term
“Dreamers’ Band,” and Stefan Schaefer, DK7FC, for “proving dreams can
come true.”
He also expressed gratitude to Warren Ziegler, K2ORS, for the
opportunity to experiment on 29 and 74 kHz, “and all the other VLF
experimenters who posted their results on the RSGB LF Group and the
Yahoo Sub 9kHz Amateur Radio group.
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