17 Jul 2010

New VLF DX record today: 5.6km on 838Hz earth mode

Today I resumed my VLF earth mode tests using 4W into 20m spaced earth electrodes. The aim of the test today was to determine the absolute maximum range possible by utilities assisted earth mode. Best result was 5.6km along Commissioner's Fen to the west of Burwell. Signals were just copied at this distance using the 80cm 30 turn loop and preamp into the PC running Spectran. A test a 6km resulted in no detectable signal.


Anonymous said...

What kind of antenna is used with this VLF SDR software? Nothing described on the Author's site.


Roger G3XBM said...

At the transmit end I'm using a pair of ground rods separated by 20m of cable fed via a 4W audio amplifier matched to around 80ohms, the load presented by the grounded electrodes. At the RX end an 80cm square loop with 30 turns is fed into a small preamp, 2 stages of Sallen-Key 50Hz filtering, passive low pass filter (VLF, MF rejection), followed by 2 stages of gain. This feeds into the line input of the PC and through Spectran software. Will add schematics for both TX and RX to my website shortly. More ongoing info at http://sites.google.com/site/g3xbmqrp/Home/earthmode