Cavechat.org

I was reading in older article about cave radios (see: http://caves.org.uk/radio/comms_in_caves.html) and the author (David Gibson) made a statement that left me with a question.

"Low frequencies are attenuated less than high frequencies - long wave broadcasts such as BBC Radio 4 (198kHz) can be detected at the bottom of deep caves. Unfortunately, detecting a radio signal is easier than transmitting it - a 200kHz signal would require an antenna some 750m long, which is normally only feasible for mining installations."

My question is: at what depth have such broadcasts been detected?

Have recent experiments been done with ground stations to attempt regionalized underground triangulation using ultra low frequency radio? I know that this is NOT useful for communication. What I'm interested in is direction, distance, and location. With the current trend of local grottos buying caves and establishing preserves there are possible locations for maintaining a 750m antenna and a radio for cave triangulation. This of course would only be one-way communication much the same as GPS.

A guy here in St Louis has a cave radio he built. two of them actually. One operates around 800hz and the other around 6800hz if Iremember right. We just used it two weekends ago to locate a dome that is scraping the surface. The 6800 hz radio even has voice communication built in, the other does not. They have been used in missouri's 4 large caves in Perry County to help find the accuracy of the maps, etc. and to even locate a junction in the 2nd longest cave in the state for drilling a new entrance. The depth of these radios can go through 600' of solid rock. They are very accurate as well. the antennas arent anywhere near 750m long, lol

See, I get so many conflicting ideas about cave radios. Does his antenna have to be grounded (connected to the dirt) in order to work? I'm trying to understand what type of radio you were using.

I'd personally like to have a set of solar powered GPS repeater stations that can be wheeled in and set up in a region. Although, at first I'd be happy with my first cave radio. Although, with the BBC channel I'm guessing that the broadcast tower is located quite some distance away instead of just on the surface.

When we were in Holloch back in the late 70's we had a long wave radio in Bivouac II so we could listen to weather reports and leave quickly if the freezing temperature moved to high in elevation. That would cause the cave to flood at the first siphon and trap us. The antenna stretched for a very long way in the cave passage. We were 3 km from the entrance and several hundred meters below the surface of the mountain.

sampson.adam wrote:See, I get so many conflicting ideas about cave radios. Does his antenna have to be grounded (connected to the dirt) in order to work? I'm trying to understand what type of radio you were using.

I'd personally like to have a set of solar powered GPS repeater stations that can be wheeled in and set up in a region. Although, at first I'd be happy with my first cave radio. Although, with the BBC channel I'm guessing that the broadcast tower is located quite some distance away instead of just on the surface.

Not grounded. No. It was all self contained and home made. This was for location purposes only. Not weather reports. Very special radios.

sampson.adam wrote:My question is: at what depth have such broadcasts been detected?

Have recent experiments been done with ground stations to attempt regionalized underground triangulation using ultra low frequency radio? I know that this is NOT useful for communication. What I'm interested in is direction, distance, and location. With the current trend of local grottos buying caves and establishing preserves there are possible locations for maintaining a 750m antenna and a radio for cave triangulation. This of course would only be one-way communication much the same as GPS.

I'm not sure at what maximum depth broadcasts have been detected, but cave radio communication has been established over 1000m below ground. Cave radiolocation is not all that uncommon in the US. If you want to do some further digging, check out Brian Pease's cave radiolocation website and this previous topic. Also be sure to check out past issues of the NSS Communication and Electronics Section publication Speleonics.