Magnetic Loop question

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Magnetic Loop question

Phillip Lontz
Are mag loop antennas very directional?
Are mag loop antennas a little directional?
Are mag loops kinda directional?
So which one?
Phil
K5SSR

What me worry?

> On Oct 19, 2016, at 9:42 AM, Richard Fjeld <[hidden email]> wrote:
>
> This is a follow up to recent post from someone in California who
> noticed less output when operating in below freezing temps.
>
> In the thread that followed, I mentioned the relationship of cold to
> gain and biasing to prevent
> thermal runaway.  My last ARRL Handbook is a 2009 edition and 'Thermal
> Runaway' can be found
> in the index.  You may find it interesting.
>
> Dick, n0ce
>
> --
>
>
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Re: Magnetic Loop question

Charlie T, K3ICH
Horizontally mounted.... No
Vertically mounted.....Yes, in the plane of the loop (off the ends NOT
perpendicular to the loop.)

Chas
-----Original Message-----
From: Elecraft [mailto:[hidden email]] On Behalf Of
Phillip Lontz
Sent: Wednesday, October 19, 2016 9:43 PM
Cc: Elecraft Reflector <[hidden email]>
Subject: [Elecraft] Magnetic Loop question

Are mag loop antennas very directional?
Are mag loop antennas a little directional?
Are mag loops kinda directional?
So which one?
Phil
K5SSR

What me worry?

> On Oct 19, 2016, at 9:42 AM, Richard Fjeld <[hidden email]> wrote:
>
> This is a follow up to recent post from someone in California who
> noticed less output when operating in below freezing temps.
>
> In the thread that followed, I mentioned the relationship of cold to
> gain and biasing to prevent thermal runaway.  My last ARRL Handbook is
> a 2009 edition and 'Thermal Runaway' can be found in the index.  You
> may find it interesting.
>
> Dick, n0ce
>
> --
>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net Please help support this email
> list: http://www.qsl.net/donate.html Message delivered to
> [hidden email]
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Re: Magnetic Loop question

W5RDW
Here is Pixel's info on their loop antenna.

http://www.universal-radio.com/catalog/sw_ant/6142dia.jpg 
Roger W5RDW
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Re: Magnetic Loop question

k6dgw
In reply to this post by Phillip Lontz
On 10/19/2016 6:42 PM, Phillip Lontz wrote:
> Are mag loop antennas very directional?

Yes

> Are mag loop antennas a little directional?

Yes, more than a little

> Are mag loops kinda directional?

The fwd lobe [in the plane of the loop] is very broad, very hard to
discern the peak, so it really doesn't matter.  The null [orthogonal to
the plane of the loop] is very sharp, very noticeable.  It can be used
to null QRN/QRM, provided of course that the QRN/QRM is located in
exactly that direction.  Fortunately, because the fwd lobe is so broad,
this actually does work fairly regularly.

K2-AlexLoop

> So which one?

See above.  I think I missed the original post [been really busy for a
retired puke], looks like the thread drifted off the question.

73,

Fred K6DGW
- Sparks NV DM09dn

- Northern California Contest Club
- CU in the Cal QSO Party 7-8 Oct 2017
- www.cqp.org

> Phil
> K5SSR
>
> What me worry?
>
>> On Oct 19, 2016, at 9:42 AM, Richard Fjeld <[hidden email]> wrote:
>>
>> This is a follow up to recent post from someone in California who
>> noticed less output when operating in below freezing temps.
>>
>> In the thread that followed, I mentioned the relationship of cold to
>> gain and biasing to prevent
>> thermal runaway.  My last ARRL Handbook is a 2009 edition and 'Thermal
>> Runaway' can be found
>> in the index.  You may find it interesting.
>>
>> Dick, n0ce
>>
>> --
>>
>>
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:[hidden email]
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>> Message delivered to [hidden email]
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]
>
>
> -----
> No virus found in this message.
> Checked by AVG - www.avg.com
> Version: 2016.0.7797 / Virus Database: 4664/13238 - Release Date: 10/19/16
>
>

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Re: Magnetic Loop question

Victor Rosenthal 4X6GP
In reply to this post by Phillip Lontz
If it is vertically polarized it has a dipole-like pattern, with sharp nulls. If horizontal, it is more or less omnidirectional.

Vic 4X6GP

> On 20 Oct 2016, at 04:42, Phillip Lontz <[hidden email]> wrote:
>
> Are mag loop antennas very directional?
> Are mag loop antennas a little directional?
> Are mag loops kinda directional?
> So which one?
> Phil
> K5SSR
>
> What me worry?
>
>> On Oct 19, 2016, at 9:42 AM, Richard Fjeld <[hidden email]> wrote:
>>
>> This is a follow up to recent post from someone in California who
>> noticed less output when operating in below freezing temps.
>>
>> In the thread that followed, I mentioned the relationship of cold to
>> gain and biasing to prevent
>> thermal runaway.  My last ARRL Handbook is a 2009 edition and 'Thermal
>> Runaway' can be found
>> in the index.  You may find it interesting.
>>
>> Dick, n0ce
>>
>> --
>>
>>
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:[hidden email]
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>> Message delivered to [hidden email]
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]
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Re: Magnetic Loop question

NK7Z
On Thu, 2016-10-20 at 12:04 +0300, Vic Rosenthal wrote:
> If it is vertically polarized it has a dipole-like pattern, with sharp
> nulls. If horizontal, it is more or less omnidirectional.
>
> Vic 4X6GP

Add enough ferrite material to do some decent choking on the feedline,
and the nulls get deeper...  Helps in DFing...

--
73's, and thanks,
Dave (NK7Z)
For software/hardware reviews see:
http://www.nk7z.net

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Re: Magnetic Loop question

Steven Dick
In reply to this post by Victor Rosenthal 4X6GP
On Thu, Oct 20, 2016 at 5:04 AM, Vic Rosenthal <[hidden email]> wrote:
> If it is vertically polarized it has a dipole-like pattern, with sharp nulls. If horizontal, it is more or less omnidirectional.
>

This is sort of incorrect.

The polarization does not matter to radiation pattern.

The physical orientation of the loop matters.   If the plane of the
loop is parallel to the ground, it is omnidirectional.

If the loop is vertically oriented, it can be horizontally or
vertically polarized, but in both cases, there is a sharp null in axis
of the loop.
(Technically, if the loop is parallel to the ground, the null points
at the ground and the sky.)
The vertical  loop can be horizontally polarized by feeding it in the
middle of the top or bottom edges.
It can be vertically polarized by feeding it in the middle of the
vertical edges.

Changing the polarization may change elevation angle, and might affect
ground wave propagated signals, but once it bounces, Faraday rotation
makes polarization irrelevant.
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Re: Magnetic Loop question

Elecraft mailing list
In reply to this post by Phillip Lontz
On Thu, 10/20/16, Steven Dick <[hidden email]> wrote:

> The vertical loop can be horizontally polarized by feeding it in the middle of the top or bottom edges.   It can be vertically polarized by feeding it in
> the middle of the vertical edges.

That's true for a loop having a full-wave circumference, but "Magnetic Loops" have circumferences that are typically only a fraction of a wavelength, and as such operate under a much different mechanism.

A vertically oriented magnetic loop, regardless of where it is fed, will achieve the highest degree of coupling to a vertically polarized signal, and have a bi-directional (half-wave dipole-like) radiation pattern.

A horizontally oriented magnetic loop, regardless of where it is fed, will achieve the highest degree of coupling to a horizontally polarized signal, and have an omni-directional radiation pattern.

This is because a magnetic loop is most responsive to the magnetic component of the RF wave.

When we speak of RF polarization, we are speaking of the polarization of the electric field.  A vertically polarized signal will have a horizontally polarized magnetic field, and vice-versa.  It is the horizontally polarized magnetic field from a vertically polarized wave front that will cut through the center of a vertically oriented magnetic loop and induce a voltage across its terminals.


73, de John, KD2BD
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Re: Magnetic Loop question

k6dgw
In reply to this post by Steven Dick
Ummm ... there may be a confusion with loops that are electrically large
... like a circumference of 360 deg.  They are E-field antennas [just
like a half-wave dipole or 1/4 wave vertical] and the feed point
determines the polarization.  Polarization matters at VHF and above, but
at HF, the received polarization will be random and changing due to
Faraday Rotation in the ionosphere.

I believe this thread is about "small magnetic loops," whose
circumference  is only a handful of degrees, such as the AlexLoop [a
resonant transformer], and others directly fed.  The feed point does not
matter for small magnetic loops.

73,

Fred K6DGW
- Sparks NV DM09dn

- Northern California Contest Club
- CU in the Cal QSO Party 7-8 Oct 2017
- www.cqp.org

On 10/20/2016 4:27 AM, Steven Dick wrote:

> The vertical  loop can be horizontally polarized by feeding it in the
> middle of the top or bottom edges.
> It can be vertically polarized by feeding it in the middle of the
> vertical edges.

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Re: Magnetic Loop question

Bill Leonard N0CU
In reply to this post by Steven Dick
"The polarization does not matter to radiation pattern. "

This isn't the case for most antennas we use which launch an electromagnetic wave by generating an electric field. Ground characteristics affect the pattern of a vertically polarized wave much more than they affect a horizontally polarized wave for these types of antennas. The mag loop however, as I understand it, launches an EM wave by generating a magnetic field. Do the ground characteristics not affect the pattern of a magnetic field the way they do an electric field? If they do have the same affect, then the above statement isn't true.

Bill  N0CU