There's been a lot of chatter in the Ham newsletters and the scientific
community about RF-signal measurements during the August 21st eclipse. But not
much has appeared in the “DX” newsletters. In the hope of stimulating an
exchange about proposed listening methodologies, we want to share the
eclipse-monitoring plan of two DX-ers...Nick Hall-Patch and myself.
We plan to take advantage of a technology that wasn't available during the last
major eclipse: the Software-Defined Radio (SDR). To give all signals an equal
chance, the Medium-Wave antennas used will be high-gain omni-directional. The
SDR listening posts at Nick's Victoria British Columbia home and my cabin in
North-Central Minnesota will be connected by a balanced wire-pair, with the
separated antennas forming a Very-Long-Baseline Eclipse-Catcher Array
("VLBECA"). RF measurements will be taken from 9.01 kHz through 66.666 MHz in
1.1-Hz increments.
For connectivity between us to form the VLBECA, we will use pair 3
(green/white) of special Cat-5 cable with pink jacketing. (From our recent
desert DXPedition we found the pink outer jacket to be the best color for
optimal velocity factor in the Cat-5, and we were already aware that an
odd-numbered pair would maintain better polarity.)
The exact distance between our two locations is 1,359.37 miles (or
2187.69395328 kilometers if you're Canadian). Since there are a lot less miles
than kilometers along the VLBECA, we chose to save money by buying the
connecting cable by the mile rather than the kilometer, and that meant
purchasing our Cat-5 in the United States.
Further input on velocity factor from the National Bureau of Standards (NBS)
led us to choose stranded rather than solid wire for the Cat-5. This created
some contention between Nick and myself, since stranded copper is more
expensive. However, when we realized the Cat-5 route took us through the
Bakken Oil Fields of North Dakota, we knew the superior mechanical performance
of stranded wire would provide additional integrity against rough handling.
For Cat-5 pair 3 termination consistency on the two ends, we asked for bids for
a pair of 2.2:1 matching transformers that would match the Cat-5’s native
110-ohm impedance to the 50-ohm input of the 273 dB-gain RF amplifier. However
no one could meet our specifications. So we ended up using the Western
Electric 111C “repeat coil” since this device is known to significantly reduce
Group Delay https://www.jmu.edu/wmra-eng/archive/repeatcoil.pdf
To guard against inaccuracies in the eclipse schedule, we agreed to begin
recording at both monitoring stations at 0301 UTC July 27th, and to conclude at
1921 UTC, September 31st. For the SDRs, 5600 Terabyte storage devices were
acquired from Best Buy.
Since we will be measuring signals expected to be at the very limits of
receiver noise performance, we spent a good deal of time thinking about
continuous battery power since, because of possible eclipse-schedule
inaccuracies, we don’t want to stop the recordings during the above period,
lest we miss something. Fortunately we were able to negotiate access to the
battery rooms of the phone companies at our respective locations. For Nick,
that’s BC Telus (formerly BC Tel; formerly the Victoria & Esquimalt Telephone
Company and the New Westminster & Burrard Inlet Telephone Company) and, for me,
the Upsala MN Telephone Company (formerly the Upsala MN Telephone Company).
Connectivity to these battery rooms will use fabric-covered lamp cord acquired
from Mark Connelly. We believe the color of the lamp cord fabric will not
impact the Group Delay.
Once the recordings have been made (assuming there really IS an eclipse) Nick
and I will meet in Salt Lake City Saturday October 7th late afteroon to review
all the recordings, and we plan to publish our results here and in QEX on
Sunday October 8th.
Please let us know if you think we’ve missed anything in our planning. Nick
and I are both “elderly” and we want to get this eclipse right so we don’t have
to wait for the next one.
Cheers!
Mark Durenberger, mobile
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