LF: Re: Induction DX?

[Roger Lapthorn <rogerlapthorn@gmail.com>]

Thanks for all the responses so far on this. 

One interesting factor which applies both to induction and earth mode (conduction) communication at VLF is the inverse cube law for attenuation. The upside of this is that if you are only trying to cover much more modest distances (1-2kms say) then the power needed is a LOT less than that to achieve twice this range or to try for DX by true radiation. 

Clearly there ends up being two distinct groups here (a) those who will be using lots of power and big antennas who should be able to get some useful amount of RF radiated below 9kHz and who have a chance of spanning some significant distances (possibly hundreds of kms), and (b) those using far more modest power levels who will only realistically be able to transmit by conduction or induction over quite local ranges. Although I shall be in the latter group because of my very limited garden size I'll be more than willing to try to receive stations seriously attempting real distance sub-9kHz.

Personally, I've quite enjoyed this whole area of discussion.

73s
Roger G3XBM

On 11 March 2010 20:54, Roger Lapthorn <rogerlapthorn@gmail.com> wrote:

If I've asked this before please forgive me....

With all the discussion recently on how to radiate a signal on sub-9kHz I'm left wondrering how far, practically, one could expect to get simply with sub-9kHz magnetic induction using multi-turn loops at each end?  The Cave Radio Group (CREG) may have some answers but I'm not a subscriber so can't read any of their documents.

It would be quite easy for anyone to generate 50-100W or so and feed this into a largish diameter multi-turn loop. Correctly aligned and with a similar loop at the far end and using decent weak signal processing just what range might be possible using modes like QRSS or WSPR? Has anyone tried this to see just what is practical, simply using induction fields?

Also, can anyone point me to some webpages with some practical audio frequency induction communication systems? There are lots of references to near field comms for on-body and inter-device comms but I've not found much otherwise.

73s
Roger G3XBM


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http://g3xbm-qrp.blogspot.com/
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http://www.youtube.com/user/G3XBM
G3XBM    GQRP 1678      ISWL G11088