Re: LF: RE: 136kHz WSPR experiment

[Roger Lapthorn <rogerlapthorn@gmail.com>]

Hi Marcin,

I agree the electrode contact should be good (into the ground) but you need the ground between the electrodes to have a low conductivity. Otherwise the "loop in the ground" is very small. The idea works best when the effective loop area is large in my view.

Mind you, I am not an expert! This is my experience and what I say could well be wrong. I have only ever used earth-electrode "antennas" with very short baselines. At the old QTH it was about 20m and at this QTH maybe 10m. In my case, certainly at 136kHz it acts like an H-field antenna. With a long baseline maybe it acts as an E-field antenna? As you can see, I talk a lot of rubbish. I'm good at that, HI. The way to find out is try it and see.

Best of luck!

73s

Roger G3XBM

On 25 January 2018 at 19:04, Marcin <bxi@go2.pl> wrote:

Hello Roger,

 

northern Poland is in majority a land of beautiful plains. Ground waters can be found already just a dozen centimetres below ground level due to depression. The conductivity in the ground could be described as good or even very good. If I wanted to set up an antenna above ground with poor conductivity I’d have to head 700 km to the south to do it. The other thing is that it would be very difficult to find a few km wide deserted spot to hang the antenna. I once tried using a 22 km long narrow gauge railway (with their consent, of course) track but over 100 year-old rails had nearly 1kOhm resistance. The electrified railway is a much better fit for this purpose as there are additional electrical connections between the rails but connecting additional grounding to those rails would cause issues with the electrical equipment and various sensors placed within the railway structure. When I did some tests once the DC (stray voltage) was ca. 20A and the voltage up to 50V. Maybe a tramway track would fit better? Unfortunately those rails in my town are not well isolated and can be partially hidden in the ground.

Ground dipole antennas will work well above the ground with god conductivity if:

• their length at least match the length of the wave
• the electrodes have a very good contact with the ground
• the wire which connects the electrodes is carefully isolated from the ground

73! Marcin SQ2BXI

 

From: owner-rsgb_lf_group@blacksheep.0org [mailto:owner-rsgb_lf_group@blacksheep.org] On Behalf Of Roger Lapthorn
Sent: Wednesday, January 24, 2018 3:00 PM
To: rsgb_lf_group@blacksheep.org
Subject: Re: LF: RE: 136kHz WSPR experiment

 

To get best results I think you need LOW conductivity around the earth-electrode "antenna", so the signal spread (and hence effective loop area) is greatest.  Placing near a river is likely to give poor results in my experience.

 

At 136kHz I suspect the earth-electrode "antenna" can be better than many solutions in the better directions (end-on), although I very much doubt that would match a good Marconi with a good ground system. My compromise vertical is NOT a very good LF/MF antenna!

 

73s

Roger G3XBM

 

On 24 January 2018 at 10:38, Marcin <bxi@go2.pl> wrote:

Hello Roger,

 

Big earth electrode antenna allows transmitting on 136kHz with average results.

https://klubnl.pl/wpr/en/index.php/2018/01/09/most-na-wisle-elementem-anteny-czyli-eksperymentow-z-dipolami-ziemnymi-ciag-dalszy/#more-720

We are slowly getting ready for testing at 8.27kHz but for this test we needed 10km of wire…

73! Marcin SQ2BXI

 

From: owner-rsgb_lf_group@blacksheep.org [mailto:owner-rsgb_lf_group@blacksheep.org] On Behalf Of Roger Lapthorn
Sent: Wednesday, January 24, 2018 10:20 AM
To: rsgb_lf_group@blacksheep.org; rsgb_lf_group@yahoogroups.co.uk
Subject: LF: 136kHz WSPR experiment

 

A couple of Gs came on. G3XIZ (46km) was 2-3dB better S/N on the earth-electrodes than on the compromise vertical. He is end-on to the "loop" in the ground. G6AVK was not copied at all. He is orthogonal to the "loop" in the ground. I was quite surprised not to spot him at all though.

 

Conclusions? The earth-electrode "antenna" in the ground is quite effective at 136kHz, but more directional.

 

Next season I will definitely try an , E-field probe on RX!

 

No great DX, but experimentation!

 

73s

Roger G3XBM