[Lowfer] LF signal enhancement - power grid coupling

[hvanesce at comcast.net]

Andy,

Some time ago I used a buried 30-meter square loop for TX below 9kHz. One
side ran near buried utility power.  A long, straight nearby road also had
buried utility power, and I measured field strength along that road at
somewhat-logarithmically-spaced intervals from 2 meters to 2.7km.

A good fit to field strength vs. distance for that case was around 1/R^1.2;
i.e. close to linear, which is interesting at those near-field (quasi-static
field) distances. 
All of the measurements were made at an estimated distance of 7 feet from
the buried utility power line, along the 2.7 km stretch of road, so this is
a measurement of some combination of the quasi-static and re-radiated
fields.
I didn't have a GPSDO when taking those measurements (i.e. I couldn't use
long integration intervals for high sensitivity), so I was unable to move
far from the buried utility power line (near which the field seemed to be
enhanced by more than 20dB) to make near-field (quasi-static field)
measurements undistorted by the utility power line. 

If one presumed that the grid was sparse in that area, the above
measurements could be used to conservatively estimate the near field
strength, and enhancement by the single grid element.    

I wish I knew what the far-field enhancement was in that case; that
parameter might apply by reciprocity to your RX case except for LF ground
effect differences between an inbound TEM signal and an almost-outbound
near-field signal. 

In any case, lots of enhancement of some kind.   

I don't know if graphics or attachments are compatible with this forum's
server. If they are, I'll send a plot and data if you're interested. The
data had an interesting frequency dependence.   

73,

Jim AA5BW

  

-----Original Message-----
From: Lowfer [mailto:lowfer-bounces at mailman.qth.net] On Behalf Of Andy -
KU4XR via Lowfer
Sent: Monday, September 5, 2016 12:19 PM
To: 1750 Meter lowfer list
Cc: Andy - KU4XR
Subject: [Lowfer] LF signal enhancement - power grid coupling

Gentlemen:

Has anyone experienced an enhancement in LF signal strength when a wire
antenna is in close proximity to a powerline ?

For years, I have had a full length 160 windom up at 30 feet.. The short leg
" was " within
12 feet of the drop-lead to my home.. I have been plagued with powerline
buzz because of the proximity, so, a few days ago, I removed the short leg,
and straped the coax braid over to the long leg.. now I have an inverted " L
",  - the powerline buzz, and overall noise level is considerably reduced, -
BUT !! - signals from MF and down - across the board - are also noticably
weaker... The antenna is still easily tuned with my LC network, but
reception seems to be much lower in strength...  I do not have a meaningful
radial field because it would be in my yard... I did not expect this
noticable drop in signals... Have I created an un-balanced dummy-load ? Now
being an Inverted " L " without a radial to work against, could that explain
the reduction in signals ?

Thanks for comments, and 73:

Andy - KU4XR
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