[IRCA] TWO DX-ERS AND THE ECLIPSE

["Mark Mobile" <Mark4@xxxxxxxxxxxxxxx>]

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 âDXâ 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-5âs 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 ârepeat coilâ 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 donât 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, thatâs 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 weâve missed anything in our planning.  Nick and I are both âelderlyâ and we want to get this eclipse right so we donât have to wait for the next one.


Cheers!

Mark Durenberger, mobile

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