I just built a rough 1 meter diameter loop using #18 wire (1mm/0.04" diameter), with wooden dowels as the form crosspieces and a small piece of cardboard separating the ends about 1/2".
Hanging the loop on an interior wooden door, and using an aade.com LC meter (I have an older one and a newer one), the older one reads 4.55 uH; the newer one reads 4.29 uH. The average of the readings gives 4.42 uH. That's very close to the 4.39 uH value of John's formula; and near to the 4.8 uH value from Jim's loopcalc calculation.
73,
Steve
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----- Original Message -----
From: "John Popelish" <jpopelish@...>
To: <loopantennas@...>
Sent: Monday, March 05, 2007 2:01 PM
Subject: Re: [loopantennas] Air core loop
Ken Javor wrote:
on 3/5/07 3:53 PM, John Popelish at jpopelish@... wrote:
exnci2000 wrote:
Hi,
I would like to know how may microhenry corresponds to a single turn
air core loop, 1 meter diameter(conductor diameter= 1 mm).I tried many
differents software but they gives different results.
regard
Is this one of the sites you found?
I agree that it doesn't agree very closely with the
approximate formula at the bottom of page 2 of:
I tend to trust sources where the formula is given, even if
they calculate for me, so I can spot check their program.
Based on the second source I think the inductance of your
loop is about 1.2 uH.
1.2 uH sounds low to me, I think it will be higher than 3
uH. But if you
have a signal source and a receiver it is easy to
measure. Construct a two
wire line that connects the signal source to the
receiver. At some
frequency around 1 -10 MHz, measure the output with the
receiver. Then
connect the loop terminals across the line. The loop will
load the line to
some degree. The degree of loading can be used to
determine the impedance
placed across the line. The impedance can be used to
back out the
inductance.
I agree that 1.2 uH seems low (gut feel) but that is what
the reference says. I checked my old Reference Data for
Radio Engineers, 5th Edition. On page 6-9 it gives this
formula:
L=(a/100)*(7.353*LOG10(16*a/d)-6.386) microhenries, where a
is the radius of the loop (to the center line of the wire),
in inches and d is the diameter of the wire, inm inches, and
that a/d>2.5
So, replacing the loop diameter of 1 meter with a loop
radius (a) of 19.69 inches, and the 1 mm wire diameter to
(d) of .039 inxches, I get an inductance of about
4.39 uH.
So we have another random data point. I haven't gone
through the formula in the above reference to check their
example (that was close ot the O.P.s case).
loopcalc.exe gives 4.8uh
73
jim ab3cv
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