Re: LF: Earth Mode

[Roger Lapthorn <rogerlapthorn@gmail.com>]

Yes Mal, let me clarify my earth electrode system here....

• A 1m copper ground stake is in the ground at the far end of my short back garden. 
• A length of 1mm diameter wire comes vertically from the far electrode for 4m then slopes upwards at about 45 degrees back to the house (17m length) then vertically downwards 4m to the upstairs bedroom window. At this point this wire is connected to the centre of 10m of coax to the front of the house where my PC and PA are located (in the shack).
• The outer of the coax is connected to the metal central heating radiator (in effect the second electrode as this connects to the copper pipes grounded outside the front of the house) 20m from the rear electrode.
• The only points of contact to ground are at each end.
  

No matching has proved necessary on 136 and 500kHz where the PA has a roughly 50 ohm output. On VLF I use a step-up audio transformer (from the 2-4 ohms of the audio PA) and I select the secondary for maximum current in the earth electrode "loop". I measured the AC resistance at between 40-60 ohms at audio frequencies but I have not checked the impedance at 136/500kHz although the antenna is a low-Q system and adjusting series capacitance at 136 and 500 does not alter the current much.

73s
Roger G3XBM

On 14 December 2010 15:52, mal hamilton <g3kevmal@talktalk.net> wrote:

LF

Although I am not intending to follow this persuit I am curious.

The confusion arises over the layout of the wires and is not made clear by anyone using the system as far as I know.

Two wires get a mention. Are they laid out across the ground like a dipole, random length and the far end earthed by an earth rod driven into the ground.

or

do the wires run in parallel and what distance apart

and

are the wires insulated, at the feed point how close are the wires, is a transformer used to match the amplifier of around 8 Ohms output to the wires and what impedence are the wires.

are the wires lying on the ground or slightly elevated ?

also

there is reference to buried pipes, elec wires etc enhancing the propagation properties of the signal but since this would be specific to the particular location

it cannot be relied upon as a statistic for a serious study how the earth mode works

As well as above there is a power consideration when trying to determin how far the signal would be received.

From information that I have the distance covered would be short, however if in some cases the wires were slightly elevated above ground even by a metre this could be considered an elevated antenna.

Could someone clarify all these ambiguites

 

I await some info

de g3kev

 

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