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Home > Archive > Electrical Engineering > January 2006 > "Shorted Turn" Phenomena ?
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"Shorted Turn" Phenomena ?
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| Robert11 2006-01-22, 3:21 pm |
| Hello:
Have a receiving only simple long wire antenna strung out my window for my
short-wave radio. Will be stringing up a new one, with different supports,
etc.
Got to wondering about this:
If the antenna wire is fastened using, e.g., metal supports, metal pulleys
or rings, that completely go 360 deg. around the wire (but are spaced from
it essentially by the wire insulation thickness, is there
any effect from the "shorted-turn" phenomena ?
Or, does the shorted turn problem only arise for a varying magnetic flux
field, and would not be applicable in this case ?
(Again, this is a receiving only application, but I guess you could argue
that there is an actual E and H field
in this receiving antenna)
Thanks,
Bob
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| bob mcree 2006-01-22, 4:21 pm |
| Robert11 wrote:
> Hello:
>
> Have a receiving only simple long wire antenna strung out my window for my
> short-wave radio. Will be stringing up a new one, with different supports,
> etc.
>
> Got to wondering about this:
>
> If the antenna wire is fastened using, e.g., metal supports, metal pulleys
> or rings, that completely go 360 deg. around the wire (but are spaced from
> it essentially by the wire insulation thickness, is there
> any effect from the "shorted-turn" phenomena ?
>
> Or, does the shorted turn problem only arise for a varying magnetic flux
> field, and would not be applicable in this case ?
yes a current is only induced in the shorted turn when there is a
varying flux. it is after all the secondary of a theoretical transformer
with the antenna being the primary. the amoung of flux in your receiving
antenna is so small that the loss is buried way below the thermal noise.
if you were using a transmitter you would not want any shorted turn
around the antenna.
-bob
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| TimPerry 2006-01-22, 4:21 pm |
|
"Robert11" <rgsros@notme.com> wrote in message
news:3oqdnaE9C5fmUE7enZ2dnUVZ_vmdnZ2d@comcast.com...
> Hello:
>
> Have a receiving only simple long wire antenna strung out my window for my
> short-wave radio. Will be stringing up a new one, with different
supports,
> etc.
>
> Got to wondering about this:
>
> If the antenna wire is fastened using, e.g., metal supports, metal pulleys
> or rings, that completely go 360 deg. around the wire (but are spaced from
> it essentially by the wire insulation thickness, is there
> any effect from the "shorted-turn" phenomena ?
in electronics everything affects everything the question is how much? in
this case not much.
first, its not a shorted turn if the wire is insulated... it just a turn or
loop. it adds inductance, in this case making the antenna seem just a bit
longer electrically.
second, the longwire should be fastened to an insulator (like a ceramic egg)
not a pulley or metal support.
safety note: some form of lightning arrester mounted outside the house and
well grounded is recommended.
>
> Or, does the shorted turn problem only arise for a varying magnetic flux
> field, and would not be applicable in this case ?
>
> (Again, this is a receiving only application, but I guess you could argue
> that there is an actual E and H field
> in this receiving antenna)
>
> Thanks,
> Bob
>
>
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| BFoelsch 2006-01-22, 5:21 pm |
| Practically, if the distance between the conductors is small compared to the
wavelength of interest, the parallel conductors will act as, well, parallel
conductors. If the spacing between the conductors is greater than, say, 1/10
wavelength then your "shorted turn" will start to have a noticeable effect.
"Robert11" <rgsros@notme.com> wrote in message
news:3oqdnaE9C5fmUE7enZ2dnUVZ_vmdnZ2d@comcast.com...
> Hello:
>
> Have a receiving only simple long wire antenna strung out my window for my
> short-wave radio. Will be stringing up a new one, with different
> supports, etc.
>
> Got to wondering about this:
>
> If the antenna wire is fastened using, e.g., metal supports, metal pulleys
> or rings, that completely go 360 deg. around the wire (but are spaced from
> it essentially by the wire insulation thickness, is there
> any effect from the "shorted-turn" phenomena ?
>
> Or, does the shorted turn problem only arise for a varying magnetic flux
> field, and would not be applicable in this case ?
>
> (Again, this is a receiving only application, but I guess you could argue
> that there is an actual E and H field
> in this receiving antenna)
>
> Thanks,
> Bob
>
| |
| Roy L. Fuchs 2006-01-22, 5:21 pm |
| On Sun, 22 Jan 2006 13:22:52 -0500, "Robert11" <rgsros@notme.com> Gave
us:
>Or, does the shorted turn problem only arise for a varying magnetic flux
>field, and would not be applicable in this case ?
A radio wave IS a variable flux field.
A radio antenna IS a transformer primary.
| |
| Roy L. Fuchs 2006-01-22, 6:21 pm |
| On Sun, 22 Jan 2006 15:22:36 -0500, "BFoelsch"
<BFoelsch@comcast.ditch.this.net> Gave us:
>Practically, if the distance between the conductors is small compared to the
>wavelength of interest, the parallel conductors will act as, well, parallel
>conductors. If the spacing between the conductors is greater than, say, 1/10
>wavelength then your "shorted turn" will start to have a noticeable effect.
This is why and how a beam antenna works to make reception
directional.
Learn to refrain from top posting in Usenet.
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