Radiation from a Loop

[D from BC]

For a loop with no ground plane:

+----------+
| |
A-+ |
|
B-+ |
| |
+----------+

Let's say the current, voltage, loop dimensions and frequency are
known across points A and B...
How do I determine if the loop is within regulation limits for
radiated EMI (ex. FCC)?


D from BC
British Columbia
Canada.

 

[Baron]

For a loop with no ground plane:

+----------+
| |
A-+ |
|
B-+ |
| |
+----------+

Let's say the current, voltage, loop dimensions and frequency are
known across points A and B...
How do I determine if the loop is within regulation limits for
radiated EMI (ex. FCC)?


D from BC
British Columbia
Canada.

Whatever you feed into the loop will be radiated. Its purely a passive
device.

 

[krw]

For a loop with no ground plane:

+----------+
| |
A-+ |
|
B-+ |
| |
+----------+

Let's say the current, voltage, loop dimensions and frequency are
known across points A and B...
How do I determine if the loop is within regulation limits for
radiated EMI (ex. FCC)?

A) Get a pile of cash and buy a spectrum analyzer and antennas
B) Take it to an EMI lab, along with a pile of cash

 

[Jamie]

For a loop with no ground plane:

+----------+
| |
A-+ |
|
B-+ |
| |
+----------+

Let's say the current, voltage, loop dimensions and frequency are
known across points A and B...
How do I determine if the loop is within regulation limits for
radiated EMI (ex. FCC)?


D from BC
British Columbia
Canada.

The FCC requires you to transmit your allowed power, not to emit freq or
harmonics out of band or wider than each segment and not disturbed other
equipment that is properly operating.

SWR (sanding wave ratio) is most likely what will get you in trouble.

This is the amount of power being reflected back to your transmitter
verses what is going out. This also causes undesired frequencies to be
generated.
You can also get this effect bouncing off structures where it may not
be apparent at the transmission sight. A field analyzer is more suited
for those situations.

 

[Vladimir Vassilevsky]

For a loop with no ground plane:
Let's say the current, voltage, loop dimensions and frequency are
known across points A and B...
How do I determine if the loop is within regulation limits for
radiated EMI (ex. FCC)?

If the wavelenth is much (say, 10 times) longer then the perimeter of the
loop, this is a trivial electromagnetic exercise. You got to know the area
of the loop S, the current I and the frequency F.

E = IS Omega Mu_0 / 2 PI R^3

If the wavelength is comparable with the perimeter of the loop, then all
depends on the geometry.

Vladimir Vassilevsky
DSP and Mixed Signal Consultant
www.abvolt.com

 

[Jamie]

A) Get a pile of cash and buy a spectrum analyzer and antennas
B) Take it to an EMI lab, along with a pile of cash

Yes., bring it to me and i'll use my cheap MFJ (mighty fine junk)
analyzer and leave the pile of cash when you go..



http://webpages.charter.net/jamie_5"

 

[D from BC]

If the wavelenth is much (say, 10 times) longer then the perimeter of the
loop, this is a trivial electromagnetic exercise. You got to know the area
of the loop S, the current I and the frequency F.

E = IS Omega Mu_0 / 2 PI R^3

If the wavelength is comparable with the perimeter of the loop, then all
depends on the geometry.

Vladimir Vassilevsky
DSP and Mixed Signal Consultant
www.abvolt.com

Interesting...

Thanks for the start.
I'll Google for more detail..


D from BC
British Columbia
Canada.

 

[D from BC]

Whatever you feed into the loop will be radiated. Its purely a passive
device.

Yeah... It radiates.
Either this is a loop antenna or a really big single turn inductor.
Dunno how to look at it..

I was looking for a max emission strength equation as a function of
I,V,f,X,Y etc.
The loop is big like 2ft x 5ft.

D from BC
British Columbia
Canada.

 

[D from BC]

A) Get a pile of cash and buy a spectrum analyzer and antennas
B) Take it to an EMI lab, along with a pile of cash

I'd like to first try to make an FCC passable design on paper.
That way I don't have to bring a pile of cash 3 or 4 more times.


D from BC
British Columbia
Canada.

 

[Terry Given]

Interesting...

Thanks for the start.
I'll Google for more detail..


D from BC
British Columbia
Canada.

or go buy a copy of "controlling radiated emissions by design", m.
mardiguan. or Ott's "noise reduction techniques in electronic systems"

Cheers
Terry

 

[D from BC]

The FCC requires you to transmit your allowed power, not to emit freq or
harmonics out of band or wider than each segment and not disturbed other
equipment that is properly operating.

SWR (sanding wave ratio) is most likely what will get you in trouble.

This is the amount of power being reflected back to your transmitter
verses what is going out. This also causes undesired frequencies to be
generated.
You can also get this effect bouncing off structures where it may not
be apparent at the transmission sight. A field analyzer is more suited
for those situations.

Great
So.. Even if I create a simple emission model, the loop can exceed FCC
limits by being in a room that creates standing waves?

Anybody here use a radiated EMI simulator?


D from BC
British Columbia
Canada.

 

[D from BC]

or go buy a copy of "controlling radiated emissions by design", m.
mardiguan. or Ott's "noise reduction techniques in electronic systems"

Cheers
Terry

Cont. Rad. Emissions by Design.
Chapter 2 page 16.
Ha! I got lucky! It's not an omitted page on Google books.
By the way, this is looking like a good book.

Thanks!


D from BC
British Columbia
Canada.

 

[Terry Given]

Cont. Rad. Emissions by Design.
Chapter 2 page 16.
Ha! I got lucky! It's not an omitted page on Google books.
By the way, this is looking like a good book.

IMO it is. very useful. which is why I wont lend my copy to anyone (its
my 2nd copy - grrr)

Thanks!


D from BC
British Columbia
Canada.

Cheers
Terry

 

[krw]

I'd like to first try to make an FCC passable design on paper.
That way I don't have to bring a pile of cash 3 or 4 more times.

Oh, if that's your only problem, just make A(Loop)=0. ;-) Other
than one of the above, I don't thing the problem is solvable, at
least without a lot more information. If it were that simple none
of us would worry about EMI tests.

 

[Terry Given]

Oh, if that's your only problem, just make A(Loop)=0. ;-) Other
than one of the above, I don't thing the problem is solvable, at
least without a lot more information. If it were that simple none
of us would worry about EMI tests.

with the formulae in Ott et al, you can get an idea of the likely field
strength. the result falls into one of 3 categories:

- way below threshold - probably OK

- way above threshold - probably bad

- somewhere inbetween - better look harder

of course in practice one does what you suggested, and forces A ~ 0 by
design (where possible). IME I generally dont calculate anything, just
implement best practice then do the tests. I have done the calcs a few
times, including at the design stage (to choose between bipolars and
BJTs in a particular app where I had to have adjacent traces running
300mm or so).

Cheers
Terry

 

[Baron]

Yeah... It radiates.
Either this is a loop antenna or a really big single turn inductor.
Dunno how to look at it..

I was looking for a max emission strength equation as a function of
I,V,f,X,Y etc.
The loop is big like 2ft x 5ft.

That calculation would give you something like the field strength in
Volts per metre in a given direction. Not that my maths are any
good. ;-)

http://en.wikipedia.org/wiki/Signal_strength

D from BC
British Columbia
Canada.

Does it really matter ? If the loop is small compared to wavelength
then the efficiency is going to be small. If its resonant then its
going to be a filter, abit a poor one. The converse is true.

If you put a dirty or clean signal into it it will still radiate that
signal. From your point of view its the equipment connected to it that
needs to be EMI clean and that includes power levels according to the
frequency band specifications.

You have no control over whether your radiated signal is going to
interact with something else to produce EMI ie rusty nail effect. To do
that needs a fairly large signal.

 

[Mark]

For a loop with no ground plane:

  +----------+
  |          |
A-+          |
             |
B-+          |
  |          |
  +----------+

Let's say the current, voltage, loop dimensions and frequency are
known across points A and B...
How do I determine if the loop is within regulation limits for
radiated EMI (ex. FCC)?

D from BC
British Columbia
Canada.

well you need the current and voltage and the phase relationship
etween them, so what you really want is the POWER going into the
loop. If you can measure or determine the REAL power going in to the
loop and the loop is a decent conductor then you can figure that all
that POWER is radiated. Then it is easy to calculate the field
strength at a distance.

Mark

 

[LVMarc]

D from BC wrote:



Whatever you feed into the loop will be radiated. Its purely a passive
device.

nonsense!