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magnetic crossed-loop antenna

magnetic crossed-loop antenna

magnetic crossed-loop antenna

(OP)
what is a magnetic crossed-loop antenna and how does it work.

RE: magnetic crossed-loop antenna

I think you are referring to antennas such as are used on MF ADF antennas on aircraft.  A pair of ferrite rods with wound resonant inductors, placed at right angles.  Each antenna has a figure-8 radiation pattern and for ADF the output of one loop at a time is summed with an E-field antenna which has an omni-directional pattern.  The result is a cardioid pattern.

The same principal applies with any pair of magnetic loops at right angles.  

Is this what you were looking for?

RE: magnetic crossed-loop antenna

(OP)
Hi
Thanks for the reply.
I am working at 100 Khz hence i cannot use E field antenna (size issues). Is it possible that I use two H field antennas placed at right angles and get a near omnidirectional radiation pattern.
How do I sum the outputs of these two antennas. I am thinking of using a combiner but would there be any phase problems.
Does an omnidirectional H field antenna exist.    

RE: magnetic crossed-loop antenna

You can use an E-field antenna.  The theory indicates that an isotropic antenna (dimensionless point in space) has only about 2.2dB less gain than a half wave dipole.  Trouble is that it's feed impedance has close to zero ohms real impedance and near infinity capacitive reactance so it's difficult to connect to a feed line.

For a receive only antenna, a short whip connected to an amplifier having a very high input impedance (which tends to swamp out the Xc component), can achieve very useful gain.  These are sold as Voltage Probe or Active Antennas and are readily available.  I saw one on a European car which used the side mirror as the antenna, but most use whips.

http://www.qrp.pops.net/probe1.htm
http://www.northcountryradio.com/Kitpages/actant.htm
http://www.arrl.org/tis/info/pdf/0109031.pdf
http://www.wellbrook.uk.com/products.html


As for combining loop antennas, the simplest thing is an input transformer with two primary windings.  Otherwise two preamps having the same gain and combined same as you would do a mic mixer.  Phase is not an issue unless your application has some special need.

RE: magnetic crossed-loop antenna

(OP)
I will read more about active antennas and probably buy one
thanks

RE: magnetic crossed-loop antenna

If I remember correctly, the crossed magnetic antennas
are fed 90 deg. out of phase to generate rotating field
pattern in the plane of both antennas.

<nbucska@pc33peripherals.com> omit 33 Use subj: ENG-TIPS
Plesae read FAQ240-1032

RE: magnetic crossed-loop antenna

nbucska - It sounds like you're referring to Circular Polarization (CP); crossed antennas fed 90-degrees out of phase. Orcus had mentioned 100kHz. CP isn't used much at LF.

Season's greetings.

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