Re: LF: Earth Electrodes

[Andy Talbot <andy.g4jnt@gmail.com>]

Yes, I suppose over the whole radiating space all you're really doing is adding the total powers of the two or more statons.   I suppose was really thinking long baselines leading to high gains - which would need some coordination and of dubious value?

 

But, if the two stations were partially in their near field regions, some additional mechanisms could perhaps come into play.   Surely two coherent sources coupling into the same E/H region could give some additional effcects - somehow.   Ideally raising the mutual radiation resistance to alter the antenna efficiency perhaps ?

 

Just throwing ideas into the air.  But at least its not technology limited.

 

A while back I remember reading Moxon's HF Antenna Book and seeing the concept of supergain coming into play - which appears to be a critical coupling thing.   Perhaps someone who understands antennas in the way Moxon did - not just being able to drive NEC - could comment?

 

Andy

www.g4jnt.com

 

 

On 14 December 2010 17:14, Roger Lapthorn <rogerlapthorn@gmail.com> wrote:

Andy,

Surely two synchronised TX systems can only increase ERP by 3dB maximum? ...or am I missing something?

Yes, 600m baseline is similar to Sanguine pro rata with frequency and that system got a megawatt TX output signal around the world and to a considerable depth in the ocean with 100% reliability. Luckily we don't need to reach the ocean floors, so our ERP can be somewhat lower (!). A 600m baseline would not be that difficult to arrange for a portable test out in the countryside or across National Trust land or woodlands.

73s
Roger G3XBM

On 14 December 2010 16:54, Andy Talbot <andy.g4jnt@gmail.com> wrote:

Google "Project Sanguine"

 

  http://www.fas.org/nuke/guide/usa/c3i/fs_clam_lake_elf2003.pdf   suggests more than 60km of cable used at 76Hz, so pro-rata not dissimiliar to 600m earth spacing at 9kHz

 

However, they do use two synchronised transmitters, so the effective baseline becomes far greater.  

 

Now, how abot that for 8970Hz.   Two stattion using low cost simple GPSDOs and similar DDS / synthesizers can reasonably guarantee their respective frequencies accuracy to 10^-9 short term  At 10kHz (to keep numbers simple), that is a differnece freq of no more than 10^-5, or 100000 seconds, or one cycle in just over a day.  And over this period, GPS derived sources will average out as spot-on.

 

So, for low cost simple amateur coherent wide spaced VLF signalling frequency is not an issue.    SIgnal element timing can be synchronised to sub microsecnds, again using GPS timing.

 

Maybe worth thinking about.   Reading the posts so far, 'JNT interest could be rekindled, so may yet apply for my NoV - although with a total house plot of only some 25 x  7  metres, there not really any scope for Tx antennas unless I use ground wires looping over the garden wall into and along the road at the back

 

Andy

www.g4jnt.com

 

 

On 14 December 2010 16:27, Chris <c.ashby435@btinternet.com> wrote:

HiStefan,

Yes, but 600m is VERY long! The wire even laying on the ground I would expect to radiate quite well at 137 with that length! And how many watts?? ERP??

I am sure 8970 would do well through the ground at the sort of powers being spoken about. Probably ideal for submarines, as Roger says!

Vy 73, Chris, G4AYT.

----- Original Message -----

From: Stefan Schäfer

To: rsgb_lf_group@blacksheep.org

Sent: Tuesday, December 14, 2010 2:49 PM

Subject: Re: LF: Earth Electrodes

Hi Chris,

But how do you explain that i have crossed 49.6 km with a 600m spaced earth electrode antenna on 8970 Hz? It was rather summer time than winther (regarding QRN)! With the same antenna, my 137 kHz signal was seen 20 dB above noise near Paris in DFCW-3!?????

73, Stefan


Am 14.12.2010 15:15, schrieb Chris:

Hi Mal,

Yes, that is what I had concluded years ago. No harm in trying though!

Further to your previous e-mail to LF, looks to me like beacons are now becoming the norm on 136/7kHz band and below. I have no problem with that personally, indeed, I think it preferable to a QSO taking forever! I woud like to see full idents though, no matter how slow.

Vy 73,

Chris, G4AYT.

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