Communication and Electronics Section

Better Caving Through Electrical Stuff

2019 Annual Convention Session Minutes

Communications & Electronics Session Minutes
2019 NSS Convention
Monday, June 17, 2019
Cookeville, TN
Brian Pease, Sec/Treas

The Session started at 2PM.

I gave my talk An Experiment to directly measure the optimum frequency for Thru-The-Earth communications with loop antennas. I designed and built gear to directly measure relative path loss at 7 different frequencies from 30kHz to 500kHz at depths to 200 meters. The gear has not been tested in a cave yet. It would involve carrying a lot of gear, some non-cave proof, both in the cave and on the surface including both radiolocation and 2-way voice gear.

Creg Cantello talked about his proposed survey system, using cameras to take multiple photos of points projected with a laser to light stations or by using pinholes in aluminum foil, then processing the images to create a 3D model. He also mentioned Microsoft Connect, which was a gaming device . The latest model (3) was a time of flight device that covered a room. He plans to have a simple demo device ready for the fall Old Timers Reunion in West Virginia.

Next, I gave my talk Comments on a proposed new high efficiency VLF miniature piezoelectric dipole for Through The Earth Communications. An open source paper titled A High Q piezoelectric resonator as a portable VLF transmitter was published in April 2019 by Mark Kemp and others. They used a 4 inch long by 5/8” diameter Lithium Niobate crystal as a dipole transmitting antenna at 35.5kHz, with incredibly narrow bandwidth. They used Direct Antenna Modulation (DAM) to shift the resonant frequency to allow FSK modulation. It cannot be used for reception. I showed that a simple 4” diameter wire loop of similar weight, and using the same transmit power, has significantly stronger Electric and Magnetic fields, with practical bandwidth and receive capability.

Sam Rowe gave the history of the Special Event ham radio station at Convention. Hev mentioned trying to recruit local hams to help, and said that he will be giving ham radio exams Tuesday evening.

Victor Orekhov of DARPA talked about the DARPA Sub-T Challenge in which teams will compete using robots to explore, search, and map underground environments such as manmade tunnels, mines, and caves. He was at Convention to see what we were doing in communications and mapping. The competition involves both physical environments and computer simulations.

John Deroo showed the Analog Devices ADALM2000 Advanced Active Learning Module, which is a USB powered, software defined instrument that allows students to work with analog and digital input and output. It can be used as an Oscilloscope, a DVM, a 50MHz spectrum analyzer, a 10MHz network analyzer, and a digital logic analyzer, using Scopy software from Analog Devices. They have a Wiki with info.
John also mentioned the ADALM-PLUTO software defined radio Active Learning Module, also from Analog Devices. It can work from 325MHz to 3.8GHz with both receive and transmit capability.

Danny Britton has built a PIC-controlled version of the 87kHz SSB Heyphone. It uses Earth Current antennas to achieve 3000 ft range in a horizontal cave, or 500-600ft depth plus 1000 ft horizontally on a good day. He has done a lot of testing.