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| Route taken from A to F (about 4km) |
Today I did a fascinating experiment on 8.977kHz VLF using my 5W earth mode transmitter and a mag-mounted E-field probe and laptop running Spectran in the car. Basically I did a "drive around" test to see where the signal could and could not be copied.
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| Signal strength on 4km run between 2 villages |
A continuous carrier was transmitted and I continuously monitored the received signal in the car. The drive was from the middle of the next village (Swaffham Prior), out through to the main road, then back along the main road to Burwell, around part of the village and then back home to the TX location. The signal was visible in Swaffham Prior at 5-10dB S/N, then disappears and returns on approaching Burwell where it is up to 40dB/S/N in 0.18Hz bandwidth. Within Burwell it is almost solid copy. The red timing ticks are every 30 seconds.
What I am detecting (I think) is the local E-field from the VLF signal in the ground, no doubt aided by local utilities. What puzzles me is why there is NO copy in between the 2 villages when there are, I think, pipes and cables in the road.
In the coming days this test is worth repeating locally in other directions and further afield. Fascinating to think a 5W VLF signal injected into the ground can be copied on a 19 inch whip on the car roof like this.
5 comments:
Interesting maybe you can't copy between the two villages because of no underground pipes or overhead electricity lines. ..._._
But there ARE these utilities between the 2 villages! That is why I am so puzzled.
Does it rely on those cables and pipes emerging from the ground to radiate. I guess much research is probably classified as it is similar to that used for submarine communications.
Yes I was wondering the same thing Bob. The H-field can be detected out to 6km from home with the 30t 80cm loop, but the E-field probe seems to detect in far fewer places, suggesting that it is either far less sensitive or that a different mechanism is needed to see the E-field component above ground. Guess who is doing some more exploring next week!
Hello Bob an Roger,
research about submarine antennas is unclassified, but is composed of hard mathematics :)
Your earth antenna is coupling to all the mettalic structires founded in the near field (in the same way has the ferrite hhihihi).
Your real antenna are this two small towns :) Maybe this is an efficient antenna in the far field.
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