[600MRG] Loop on the ground

Sun Mar 1 16:52:05 EST 2020

Many thanks to all who responded and here is how it went after reading 
your fine posts;

It was obvious that there are many different sounding noise signals on 
630m but I only have a simple 2 antenna input so far on the noise phaser..

1. This vertical litz transmit 350' loop is by far the most sensitive 
antenna for 630m reception so it is #1 input to the phaser....

2. After digesting all of the replies here I ran a 300' coax. loop on 
the ground.. Shield is grounded and it has a very good signal to noise 
ratio but is not hearing DX so well as the vertical.. The LOG does 
however hear a lot of different QRN of all sorts.. The loop on ground is 
located just beneath the 350' vertical litz transmit loop..

3. The loop on ground is fed with 75 ohm twin lead and it looks to be in 
phase or out of phase ?? with the vertical and the phaser does cause a 
very deep null on background noise using the twin lead in from the LOG, 
terminated in a binocular transformer and transferred to the system at 
nearly 50 ohms.. The shack end of the 75 ohm twin lead has a 500 ohm 
variable resistor across the twin lead.. The center pin is grounded and 
really causes a deep null at the shack, 10-20 db..... Am able to find 
different 'grounds' and then tune accordingly... Just 'rack' ground in 
the shack seems to yield best S/N..

** EXTRA freebee yield; With a .3 MH high Q inductor in series with the 
TX loop and a .1ufd cap. ( L network ) the 630m transmit loop hears 
16-60 khz. with VERY low noise... Am seeing clear VLF NAA type signals ( 
6 or 7 ) and some others not identified.. 17.2 khz 'SAQ' is located at a 
noise null here as it turns out :-).. 20khz time and 60 khz time sigs 
are very out of the noise...ï¿½ NAA on 24 khz. wins s/n at 62 db above the 
ambient noise... Wonder how that stacks up against other findings??

Special thanks to Matt, KA1R who has been compiling 630m sigs to and 
from the Atlantic and EU stations.. I was resigned to living in a high 
noise environment util http://njdtechnologies.net/030120/ gave clues to 
the answer concerning RX noise..

Thanks All, and very 73s from DaveR aa1a

On 2/9/2020 6:04 PM, Rudy Severns wrote:
>
> Dave,
>
> The answers to RX antenna questions will depend strongly on the 
> particular situation at a given QTH. ï¿½I spent the last year 
> frantically trying many different RX antennas but ended up learning 
> about reality.
>
> First, how close, in wavelengths, is the RX antenna to the noise 
> source(s).ï¿½ Anything less than 1/4 wave means youï¿½re in the inductive 
> near-field.ï¿½ A quarterwave on 630m is about 500ï¿½ and 3600ï¿½ on 2200m.ï¿½ 
> When you model RX antennas within that distance you have to look at 
> the near-field pattern which is often very different from the 
> far-field pattern.
>
> Second, power lines are a combination of horizontal wires with 
> occasional (or frequent) service transformers and drop lines which 
> have a vertical wire from each transformer to a ground stake.ï¿½ This 
> means you have both vertical and horizontal RFI currents.
>
> The magnetic field from the horizontal lines will couple very nicely 
> into a horizontal loop, in the air or on the ground.ï¿½ They also couple 
> nicely with vertical loops parallel to the lines.ï¿½ The vertical ground 
> wires couple nicely into vertical loops perpendicular to the lines. 
> ï¿½ï¿½In my case where the lines are perpendicular no matter what 
> direction I point a vertical loop I get really great reception of the 
> line RFI.ï¿½ I have a loop mounted on a rotor which shows a very sharp 
> null for sky-wave signals but no help at all for the line RFI other 
> than to move the bars on the waterfall display around.
>
> I have the worst of all: power lines, all well within the near-field, 
> in the form of a T.ï¿½ My greatest distance from a line is 400ï¿½.ï¿½ On my 
> south boundary I have a polyphase industrial service running E-W 
> forever.ï¿½ On my west boundary I have a branch line, also polyphase, 
> running N-S. In most urban areas (Iï¿½m out in farmland BTW) thisï¿½ would 
> be a typical geometry.ï¿½ You are likely to be surrounded with lines.ï¿½ 
> Erecting a vertical loop is the same as adding a secondary winding to 
> a transformer, i.e. the power lines are the primary.ï¿½ Forget 
> radiation, this is just plain old inductive coupling. Horizontal 
> loops, BOGï¿½s, Beverages, etc, same problem.ï¿½ Laying down a 700ï¿½ BOG 
> greatly improved my reception of the power line RFI.
>
> In my situation at least, the noise is mostly horizontal from the 
> lines and to a much lesser extent vertical from the vertical grounding 
> wires.ï¿½ The near-field usually falls roughly as the inverse of the 
> cube of distance. My best antenna is a simple vertical located in the 
> far N-E corner of my property.ï¿½ As discouraging as my situation is all 
> is not lost, I still decode VK4YB WSPR on 2200m regularly.
>
> 73, Rudy N6LF
>
>
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