# Simulate RF interference coupling prior to testing

Started by July 4, 2020
```I have a circuit that must operate next to a stong RF tranmitter (long
rnage communication)   Frequencies could be form MHz to Single GHZ
range.

what would be the best way to simulate a circuit in spice with a field
farying RF fleid impenging on it.

capacitove coupling?  inductive coupling?   other spice coupling
method?

The circuit dues have a single uH inductor connector to a diode and a
capacitor in a toplolgy similar to a boost regulator.   I would like to
simulate which conditions could cause the RF to create enought engergy
that could be restified by the diode and create voltage on the
capacitor.

The output of this circuit is loaded with 1 ohm (resistive) so it would
need to have some current drive to generate much voltage but I am
wondering how to simulate how strong of a field could drive enought
current to overvoltage the circuit.

thanks
```
```On Saturday, July 4, 2020 at 4:41:02 PM UTC-4, mook Jonhon wrote:
> I have a circuit that must operate next to a stong RF tranmitter (long
> rnage communication)   Frequencies could be form MHz to Single GHZ
> range.
>
> what would be the best way to simulate a circuit in spice with a field
> farying RF fleid impenging on it.
>
> capacitove coupling?  inductive coupling?   other spice coupling
> method?
>
> The circuit dues have a single uH inductor connector to a diode and a
> capacitor in a toplolgy similar to a boost regulator.   I would like to
> simulate which conditions could cause the RF to create enought engergy
> that could be restified by the diode and create voltage on the
> capacitor.
>
> The output of this circuit is loaded with 1 ohm (resistive) so it would
> need to have some current drive to generate much voltage but I am
> wondering how to simulate how strong of a field could drive enought
> current to overvoltage the circuit.
>
> thanks

There are so many ways for RF to get into your circuit.  You have to gp through each path one by one
```
```mook Jonhon puked:

=================
>
> I have a circuit that must operate next to a stong RF tranmitter (long
> rnage communication)   Frequencies could be form MHz to Single GHZ
> range.
>

** Sounds like a nightmare situation that ought to be AVOIDED in the first place.

> what would be the best way to simulate a circuit in spice with a field
> farying RF fleid impenging on it.

** Bonkers idea to even try.

Only real tests on a prototype have any value.

.....   Phil
```
```On Sat, 04 Jul 2020 20:40:57 GMT, "mook Jonhon" <mook@mook.net> wrote:

>I have a circuit that must operate next to a stong RF tranmitter (long
>rnage communication)   Frequencies could be form MHz to Single GHZ
>range.
>
>what would be the best way to simulate a circuit in spice with a field
>farying RF fleid impenging on it.
>
>capacitove coupling?  inductive coupling?   other spice coupling
>method?
>
>The circuit dues have a single uH inductor connector to a diode and a
>capacitor in a toplolgy similar to a boost regulator.   I would like to
>simulate which conditions could cause the RF to create enought engergy
>that could be restified by the diode and create voltage on the
>capacitor.
>
>The output of this circuit is loaded with 1 ohm (resistive) so it would
>need to have some current drive to generate much voltage but I am
>wondering how to simulate how strong of a field could drive enought
>current to overvoltage the circuit.
>
>thanks

I doubt that Spice will tell you much.

In my experience, emi sensitivity is much worse in narrow bands where
boxes, boards, and cables resonate. That often happens in to 100-300
MHz range.

--

John Larkin         Highland Technology, Inc   trk

The cork popped merrily, and Lord Peter rose to his feet.
"Bunter", he said, "I give you a toast. The triumph of Instinct over Reason"
```
```On Saturday, July 4, 2020 at 1:41:02 PM UTC-7, mook Jonhon wrote:
> I have a circuit that must operate next to a stong RF tranmitter (long
> rnage communication)   Frequencies could be form MHz to Single GHZ
> range.
>
> what would be the best way to simulate a circuit in spice with a field
> farying RF fleid impenging on it.

Well, it can certainly be done; probably at low impedance the magnetic
coupling would dominate, and at high impedance capacitive will
dominate, but...

your components have resonances that will have to be modeled; how
complex a SPICE model do you expect to support?

What is the GHz impedance of an electrolytic capacitor?   I don't know,
but it's the kind of thing that has to go into your model.   Series resonant
frequency of inductors is something usually specified, but of other

Me, I'd make a paddle out of something conductive or magnetic,
and wave it around until I found a position that attenuated the crosstalk,
and put a shield there.
```
```whit3rd is raving luntatic &  grade A idiot wrote:

================================================

>
>
> Well, it can certainly be done;

** Bollocks.

Beware of this trolling, nut case, retard and congenital LIAR.

His idiot, fake handle ought be fair warning.

....   Phil
```
```On 04/07/20 21:40, mook Jonhon wrote:
> I have a circuit that must operate next to a stong RF tranmitter (long
> rnage communication)   Frequencies could be form MHz to Single GHZ
> range.
>
> what would be the best way to simulate a circuit in spice with a field
> farying RF fleid impenging on it.
>
> capacitove coupling?  inductive coupling?   other spice coupling
> method?
>
> The circuit dues have a single uH inductor connector to a diode and a
> capacitor in a toplolgy similar to a boost regulator.   I would like to
> simulate which conditions could cause the RF to create enought engergy
> that could be restified by the diode and create voltage on the
> capacitor.
>
> The output of this circuit is loaded with 1 ohm (resistive) so it would
> need to have some current drive to generate much voltage but I am
> wondering how to simulate how strong of a field could drive enought
> current to overvoltage the circuit.

RF interference is /very/ dependent on the /details/
of the two systems, including their relative orientations
and the external surroundings.

A spice simulation could, /at best/, give you information
about one point in that design and implementation space.

Where circuits must be immune to RF interference, they
techniques are based around presuming worst-case
behaviour. The prediction and assessment of worst-case
behaviour is a highly specialised skill, and even then
it will be supplemented by careful testing.

Summary: I don't think you will be able to achieve your
```
```EMI reduction uses the following strategies;

Your hypothetical model is not good enough. Needs more details.

****
Shielding: single or double, absorption vs reflection: ingress & egress
Orientation: & fringe effects
Separation: waves {Plane,wire,point} source varies to order {1,2,3}
Balancing: Differential and Common mode, Baluns and INA's
Filtering: Pass the signal, Attenuate the noise,
Impedance ratios: Source to Load with path loss and wave transformation

Can you model a slot in a shield as a wire ?
Can you design microstrip or lumped filters then add wave mechanics to
get lumped elements on schematic to simulate a simple wire or structure.

Do you know the ESR, inductance or capacitance of wire?**

Do you know Mutual Coupling is just a ratio from C to C or L to L?
This is like crosstalk from C to Z or L to Z.

Can you do it on Spice?  Not likely.
Although I have done it on Falstad's Sim.,
You may use tools like COMSOL to simulate the physics, or build and test
it with a Network Analyzer or Spectrum Analyzer & scope is more likely.

- You can use the model solutions I listed above **** to know what works
best.. and estimate values with **

Read the EMC book by Henry Ott as I did over 40 years ago.

It will give you more than my quick summary of my EMI experience.

One problem of interest was in early 80's when Burroughs had computers
with large 14" disk drives on the top floors of the biggest Financial
Investors. They were so  "big" they had a bylaw that no other building
in the city could be bigger.  They discovered the data would get random
data errors and discovered it was from the 1 second rotating RADAR at
the international airport 10 miles away which used kW microwave pulses
that got into the high impedance Read Data magnetic signals.   (Fixed
with braid shielding)
```
```On 07/05/20 02:19, whit3rd wrote:
> On Saturday, July 4, 2020 at 1:41:02 PM UTC-7, mook Jonhon wrote:
>> I have a circuit that must operate next to a stong RF tranmitter (long
>> rnage communication)   Frequencies could be form MHz to Single GHZ
>> range.
>>
>> what would be the best way to simulate a circuit in spice with a field
>> farying RF fleid impenging on it.
>
> Well, it can certainly be done; probably at low impedance the magnetic
> coupling would dominate, and at high impedance capacitive will
> dominate, but...
>
> your components have resonances that will have to be modeled; how
> complex a SPICE model do you expect to support?
>
> What is the GHz impedance of an electrolytic capacitor?   I don't know,
> but it's the kind of thing that has to go into your model.   Series resonant
> frequency of inductors is something usually specified, but of other
> components, you're on your own.
>
> Me, I'd make a paddle out of something conductive or magnetic,
> and wave it around until I found a position that attenuated the crosstalk,
> and put a shield there.

You can model all you like and spend \$k on it, but the only way to
really prove it is to build a prototype, in it's intended enclosure,
put it in screened room and measure it. Too many variables
to affordably model it, though no doubt some will try...

Chris

```
```On Sat, 4 Jul 2020 18:19:53 -0700 (PDT), whit3rd <whit3rd@gmail.com>
wrote:

>On Saturday, July 4, 2020 at 1:41:02 PM UTC-7, mook Jonhon wrote:
>> I have a circuit that must operate next to a stong RF tranmitter (long
>> rnage communication)   Frequencies could be form MHz to Single GHZ
>> range.
>>
>> what would be the best way to simulate a circuit in spice with a field
>> farying RF fleid impenging on it.
>
>Well, it can certainly be done; probably at low impedance the magnetic
>coupling would dominate, and at high impedance capacitive will
>dominate, but...
>
>your components have resonances that will have to be modeled; how
>complex a SPICE model do you expect to support?
>
>What is the GHz impedance of an electrolytic capacitor?   I don't know,
>but it's the kind of thing that has to go into your model.   Series resonant
>frequency of inductors is something usually specified, but of other
>
>Me, I'd make a paddle out of something conductive or magnetic,
>and wave it around until I found a position that attenuated the crosstalk,
>and put a shield there.

Do the opposite: connect a short stub antenna to a signal generator,
plop it here and there, and sweep the frequency to find sensitivities.
Fix them.

They broke up some serious high-Q resonances.

That's a thermocouple input. The competitor's version of this
controller could be shut down from clear across the room, with a
modest signal generator. That wasn't pupular in an NMR system.

--

John Larkin         Highland Technology, Inc   trk

The cork popped merrily, and Lord Peter rose to his feet.
"Bunter", he said, "I give you a toast. The triumph of Instinct over Reason"
```