Message-ID: <001801c0f80f$668d2d60$b10e883e@robing>
From: "Robin T. Greenwood" <robin@g3lba.freeserve.co.uk>
To: rsgb_lf_group@blacksheep.org
References: <7D653C9C42F5D411A27C00508BF8803D55C4F1@pdw-mail-r1.dstl.gov.uk>
Subject: LF: Re: RE: Anyone using a magnetic loop for 13	6 Khz?
Date: Mon, 18 Jun 2001 16:57:31 +0100
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There was  a nice design  recently (2yrs?) in RadCom.
Robin G3LBA

----- Original Message -----
From: "Talbot Andrew" <ACTALBOT@dera.gov.uk>
To: <rsgb_lf_group@blacksheep.org>
Sent: Monday, June 18, 2001 4:19 PM
Subject: LF: RE: Anyone using a magnetic loop for 13 6 Khz?


> Another example of a reply without the original posting being returned,
what
> is going on ?
> Anyway ...
>
> I'll send the spreadsheet direct.
>
> Turns were spaced about 50mm apart - defined by the standard pipe clips
for
> this tubing.
> The effect of N turns over a single turn loop is to :
> Increase the Radiation resistance by N^2
> Increase the loss resistance by N
> Increase the inductance by very nearly N^2
> Increase the copper in the air by N
>
> Hence efficiency goes up roughly proportional to N.  Efficiency is also
> proportional to amount of copper in the air - which seemed to be a
> reasonably acucrate rule of thumb true whatever combination of turns, wire
> thickness, wire type I tried to use in the calculations.
>
> The loop was series resonated with around  110nF (for 73kHz) of high
voltage
> polystyrene caps and passed as one turn through an ETD44 ferrite core.
This
> winding was made from the braid from UR67 coax, but its length was short
so
> didn't add much extra loss.  The feed was into the multiturn primary of
this
> transformer.  In those days I was using an audio amplifier, feeding the
> primary direct from its  8 ohm output via home made Litz wire.  Calculated
> loss resistance of this loop was around 0.06 ohms, based on skin depth
> calculations.  The actual loss resistance figure measured as less than 0.1
> ohms so I was confident in the calculations - the extra was due to series
R
> in the caps and proximity effects to ground.   Measuring parameters on a
> loop antenna are very straightforward - simple application of equations
for
> Q / Bandwidth can soon show how close theory is to practice, and I always
> found good correlation between the two.
>
> When the loop becomes very big there comes a point where its efficiency
> begins to rival or even exceed that of wire antennas.  Only one or two
> operators have ever got that far on LF - G2AJV was one of them with a huge
> loop over several hundred m long, seem to recall,  by several metres high.
>
> But as stated in the last EMail - small loops have nothing to offer
against
> wire antennas where space is limited.
>
> Andy  G4JNT
>
>
> > -----Original Message-----
> > From: Paul A. Cianciolo [mailto:paulc@snet.net]
> > Sent: 2001-06-18 14:56
> > To: rsgb_lf_group@blacksheep.org
> > Subject: LF: Re: RE: Anyone using a magnetic loop for 136 Khz?
> >
> >
> > Andy,
> > Thanks for the response!!!!!
> > WOW !  Do you still have a copy of the spreadsheet?
> > I would love to see a copy.
> >
> > It seems like 10 Db down was not so bad considering how small
> > the loop was.
> > I have the means to support a loop with the apex at over 100 feet.
> >
> > I have not seen any info on multiturn magloops.  Please help I am very
> > interested.
> >
> > >
> > >
> > > > -----Original Message-----
> > > > From: Paul A. Cianciolo [mailto:paulc@snet.net]
> > > > Sent: 2001-06-18 13:38
> > > > To: rsgb_lf_group@blacksheep.org
> > > > Subject: LF: Anyone using a magnetic loop for 136 Khz?
> > > >
> > > >
> > > > Hello Folk.
> > > >
> > > > I have had a sudden interest in small manetic transmitting
> > > > loops lately.
> > > > Have seen manty designs for 160 meters and above but not too
> > > > much on LF.
> > > >
> > > > Anyone running one of these at 136Khz?   How is the
> > feeding done?\\
> > > >
> > > > Most designs that I have seen use tubing to reduce the I*R
> > > > losses.  Do to
> > > > skin effect I realize that current flows only on the
> > > > surface of the conductor.  This maseem like a very basic
> > > > question but do
> > > > current flow on the inside of the tubing?
> > > > And if it does of what use is it?  Seems to me like it would
> > > > not be useful
> > > > for radiating purposes since it is inside of a shielded pipe.
> > > >
> > > > Would not a flat strap cable be better?
> > > >
> > > >  Thank you
> > > >
> > > > Looking toward 136 Khz!!!!!!!
> > > >
> > > >
> > > > Paulc
> > > > W1VLF
> > > >
> > > > Cloudbounce Webpage  http://www.qsl.net/w1vlf/
> > > > Rescue Electronic Surplus http://www.rescueelectronics.com
> > > >
> > > > 1982 Vanagon Diesel  Turbo Diesel 1.9
> > > > GE Electrak E20 and E15  electric tractors
> > > > First place in local tractor pulls  at 1750 LBS
> > > > With Stock E-20 Electric tractor
> > > > Air Rifle Target Shooting Enthusiast
> > > >
> > > >
> > > >
> > >
> > >
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