Content-Transfer-Encoding: 8bit
Message-ID: <7D653C9C42F5D411A27C00508BF8803D55C4F1@pdw-mail-r1.dstl.gov.uk>
From: "Talbot Andrew" <ACTALBOT@dera.gov.uk>
To: rsgb_lf_group@blacksheep.org
Subject: LF: RE: Anyone using a magnetic loop for 13	6 Khz?
Date: Mon, 18 Jun 2001 16:19:16 +0100
MIME-Version: 1.0
Content-Type: text/plain; charset=iso-8859-1; format=flowed
Precedence: bulk
Reply-To: rsgb_lf_group@blacksheep.org
Sender: <majordom@post.thorcom.com>

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
> > >
> > >
> > >
> >
> >
> > --
> > The Information contained in this E-Mail and any subsequent 
> correspondence
> > is private and is intended solely for the intended recipient(s).
> > For those other than the recipient any disclosure, copying, 
> distribution,
> > or any action taken or omitted to be taken in reliance on 
> such information
> is
> > prohibited and may be unlawful.
> >
> 
> 


-- 
The Information contained in this E-Mail and any subsequent correspondence
is private and is intended solely for the intended recipient(s).
For those other than the recipient any disclosure, copying, distribution, 
or any action taken or omitted to be taken in reliance on such information is
prohibited and may be unlawful.