[Lowfer] Small loop calculator

Tue Jun 9 02:19:58 EDT 2009

Thanks Bill - long time as you say  - Well I'm getting my dream of being home for just a couple of weeks in KL7 - ! Sheri talks about the Loons and the swans and mostly the B52 Mozzies... 

Well the ground is going to way different than any of my previous QTH's and its going to be an experience.

I have 1 foot of "Organics and Silt", then 11 foot of Gravel and Sand with occasional up to 16 inch cobbles and then hit ground water....next to a lake and all that - Mostly Silver Birch with the occasional Taller Evergreen  - Hmmm...

Well from the graphs and plots I should be dealing with much lower impedances and reactance's at 500 K if I keep it to just less than a 1/4Y but I notice some oddities so as ever its going to be plug and play. - looks like I should stay way away from 1/2Y as ever... I read with interest John TAGs 137/500 loop results where losses and gains sort of crossed out each other, but I guess we will work empirically - What got me from the graphs was the huge increase in efficiency as you get to longer lengths - much more than I realized....

Ive been reading a lot (not much else to do)  and when in Singapore played a lot with HB VLF portable receivers and short 1m whips - Singapore is surprisingly pretty dang quiet Hum and Hum harmonic  wise due to everything being underground, so your hear the constant tweek, bangs and all that - 

What I did notice was the "dumping" the field -effects the trees had at these freqs and really how far these 1Mohm Z receivers or so were affected by them - you had to go (in some cases) 15-30m or more away or the signals disappeared or were severely attenuated, again Tree type/size dependant - .

 I know the loop being at the relative other end of the scale is (far far) less affected given the results at XDW et al -  but I'm wondering more and more about the probes at LF, which in order of magnitude have the same sort of Input Z, and ok your up the band a bit but wondering just how much we are effectively reducing the field too in real terms. You'll remember me playing with various flora over the past years - sometimes probes work better close to trunks, optimum height, different type of tree - some having positive effects (Acacia) and some not - (Palm trees) - but over all just how much better would it be to get the sucker above the tree line and out into space and clear air above these 100K resistors -  . 

I know how this is for buildings of course but even then some buildings have a remarkable different characteristic of the "best" position for a probe - on a corner, out and above over the side, or above in the middle etc... I still favor a reinforced concrete apartment block with metal door frames and doors, which in most cases are  bonded back to that reinforcing by hook and crook,. and something to bond the outer of the coax from the probe to, knocking off 40dB of common noise crud coming from inside this de facto "Faraday cage" - unfortunately our lovely ranch house is wood with little or no reinforcing - so far earth rods and chokes have only partially dumped the crud coming up the coax to ground - Ill need to work on that more..no Faraday cage in KL7...:-((

Ill let you know how it goes but have important work like dealing with sump pumps, replacing our RF balun low temperature garage flouri tubes which more crud out on LF/MF than you would believe - back to normal Copper Iron Balun types etc  and having BBQ's etc (dang it  - theres a burn ban...)

I like the idea of "Green building" twofold - obviously Eco wise - and  used to have all our Antarctic bases building painted light or dark Green - good thermally and supposing relaxing for Humans..a sense of home in a supposed White world. After 3 years down there without a break I nearly forgot what Green looked like.

Cheers
Laurence KL1 X
WE2XPQ

Presently BY3A- KL1X China

--Bill said

"Unfortunately 99% of my loop experimentation was in Andover, MA, at 185K and I can only conjecture what happens when a traditional LF loop is operated at 500K. One of my my 200ft diam Ashlock Loops up north uses 3/8s inch CU tubing and behaves at 500K fairly close to how it  behaves at 185K. Meaning that the measured Rac, results using ferrite step-down Xfmrs, resonating approaches, and radiation patterns are similar. The loss from resting on trees has yet to be measured.

Not sure what your soil conductivity will be like in Alaska but I have shown at 185K that soil conductivity has a marked effect on a loop's signal - both sky wave and surface wave. I have two I identical antennas set up to demonstraight this - one in Ellsworth and one in Andover running exactly the same current. Last winter the loop in Andover consistently showed up on the Grabulator (sky wave propagation) with over 6db of signal strength over the Ellsworth loop. Reports from approx 1000 mi, although far less regular, were similar. Also the falloff with distance in the 10 to 50mi surface wave range is much greater for the Ellsworth loop. Will be really interesting to run the same test at 500K and plan to do this next winter.

Wish I could offer more help. The house-building in Ellsworth which has turned into a 'supper green' design has all but consumed all my available time."

Bill 

> From: hellozerohellozero at hotmail.com
> To: lowfer at mailman.qth.net
> Date: Fri, 5 Jun 2009 22:38:50 -0800
> Subject: [Lowfer] Small loop calculator
> 
> 
> 
> 
> If been trying to calculate what sort of Voltages and impedances Im going to be faced with on my LF/MF loop in Alaska at 505-510kHz compared to 137khz and been fiddling with the values of
> 
> length diameter, capacitor values and voltages...
> 
> 
> 
> http://www.66pacific.com/calculators/small_tx_loop_calc.aspx
> 
> 
> 
> Im not sure given the real world of heights, ground permitivity, true conductor/skin whether it holds thru but plumbing in the figures for past oprations, in order of values it appears to give rationale figures. In all cases it tells me to keep the length less that 0,25Y...
> 
> 
> 
> Other good educational reading and the politicking of when a small becomes intermediate or large, and some good telling graphs on the links below.
> 
> 
> 
> http://personal.ee.surrey.ac.uk/Personal/D.Jefferies/loop.html and
> 
> http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=15200
> 
> 
> 
> 
> 
> Anyone have any novel methods of feeding say a 470ft circumference loop at 505khz down to coax in the end welcomed....
> 
> 
> 
> Laurence WE2XPQ as of next week...
> 
> BP51 Wasilla AK
> 
> 
> 
> Presently OM89UA China.
> 
> 
> 
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