A near field RF jammer?

[Moreno]

Which relatively simple and inexpensive device is capable to create strong broadband EMF interference in a near field (1-3 m) zone? Approximately it has to jam any signal in the 1 MHz - 10 GHz range or so. Are transformers, Van den Graaf generators, metal detectors or induction Owens capable to do something like this? What about zummers or negative ion clouds?

 

[Carrock]

1 hour ago, Moreno said:

Which relatively simple and inexpensive device is capable to create strong broadband EMF interference in a near field (1-3 m) zone? Approximately it has to jam any signal in the 1 MHz - 10 GHz range or so. Are transformers, Van den Graaf generators, metal detectors or induction Owens capable to do something like this? What about zummers or negative ion clouds?

 

There are various quite cheap options.

I'll answer a simpler question:

Is there a legal way to do the above?

No.

Edited September 30, 2017 by Carrock

[John Cuthber]

It wouldn't be legal. Also, to cover that range would also be difficult.

[Moreno]

11 minutes ago, Carrock said:

There are various quite cheap options.

I'll answer a simpler question:

Is there a legal way to do the above?

No.

I'm not sure. Plenty of household appliances can create an EMF interference. I don't think a legal organizations are commonly troubled with someone who posesses a transformer or Tesla coil for example. The most important it doesn't suppose to affect someone else, such as your neighbours, for example. At a few meters effective area this is practically impossible. I know they experiment with a wireless chargers and data transfer using magnetic resonance between two coils. It does have range up to a few metres. What can be done to make those coils to generate broadband rf notice instead of specific frequency? This interference will not affect area outside a few meter range in any case.

 

[Carrock]

You specifically asked about intentional jamming. Intent is legally important in this context.

'jam any signal in the 1 MHz - 10 GHz range or so' up to about ~3m jams weak signals much further away.

As its easy to look up I'll mention the spark gap transmitter which is/was specifically banned in some radio licenses and should soon have the authorities coming round to confiscate your equipment and take you to court.

 

[Moreno]

33 minutes ago, Carrock said:

You specifically asked about intentional jamming. Intent is legally important in this context.

'jam any signal in the 1 MHz - 10 GHz range or so' up to about ~3m jams weak signals much further away.

As its easy to look up I'll mention the spark gap transmitter which is/was specifically banned in some radio licenses and should soon have the authorities coming round to confiscate your equipment and take you to court.

 

An intent is not necessary illegal. For example passive radio jamming is not restricted I think, such as using a Faradey cage, for example. I don't know how spark gap transmitter works, but I have doubts it is near field generator. More likely it is a far field and this is why police may get interest in it.

 

[Carrock]

2 minutes ago, Moreno said:

An intent is not necessary illegal. For example passive radio jamming is not restricted I think, such as using a Faradey cage, for example. I don't know how spark gap transmitter works, but I have doubts it is near field generator. More likely it is a far field and this is why police may get interest in it.

Attenuation isn't jamming and doesn't generate interference so is usually perfectly legal and not much use for blocking.

I don't think intending and failing to create a jammer is illlegal.

From https://en.wikipedia.org/wiki/Faraday_cage

Quote

A common misconception is that a Faraday cage provides full blockage or attenuation; this is not true. The reception or transmission of radio waves, a form of electromagnetic radiation, to or from an antenna within a Faraday cage is heavily attenuated or blocked by the cage, however, a Faraday cage has varied attenuation depending on wave form, frequency or distance from receiver/transmitter, and receiver/transmitter power. Near-field high-powered frequency transmissions like HF RFID are more likely to penetrate. Solid cages generally provide better attenuation than mesh cages.

Without an aerial, a spark gap transmitter is mostly but not entirely near field; I doubt you could create a near field noise generator for 1 MHz - 10 GHz with a range close to 3m throughout the entire range without significant far field.

If you happen to be close to (the line of sight of) an important microwave link and block it with interference, I doubt you'd get much sympathy even if you could prove 99% of the generated noise was near field.

[Moreno]

2 minutes ago, Carrock said:

Without an aerial, a spark gap transmitter is mostly but not entirely near field; I doubt you could create a near field noise generator for 1 MHz - 10 GHz with a range close to 3m throughout the entire range without significant far field.

What is an "aerial"? Transformers create near field at 50 Hz and this is still near field regardless giant wavelength of a separate 50 Hz wave? Also I care most about 1-10 GHz range, MHz range is of lower priority.

 

[rangerx]

A lay person cannot build and/or operate  any transmitting device without licensing. Even certified RF engineers and technicians building or servicing legal devices must adhere to  laws respecting allocated frequencies, co-channel dependencies (duplex channels),interference  from resonate images (IF) and input (watts) or output power (ERP).

Certified and licensed amateur radio operators (Hams) may build and operate their own equipment, but may only operate within the frequency bands allocated to them and without spurious or parasitic interference to other users. Even otherwise compliant devices cannot be used to interfere with other lawful users, for any reason.

Unauthorized RF signals are simple to detect with radio direction finders (RDF), frequency counters and near field detectors. FCC inspectors have the same clout as most law enforcement agencies when it comes to search, seizure and prosecution.

[Moreno]

54 minutes ago, rangerx said:

A lay person cannot build and/or operate  any transmitting device without licensing. Even certified RF engineers and technicians building or servicing legal devices must adhere to  laws respecting allocated frequencies, co-channel dependencies (duplex channels),interference  from resonate images (IF) and input (watts) or output power (ERP).

Certified and licensed amateur radio operators (Hams) may build and operate their own equipment, but may only operate within the frequency bands allocated to them and without spurious or parasitic interference to other users. Even otherwise compliant devices cannot be used to interfere with other lawful users, for any reason.

Unauthorized RF signals are simple to detect with radio direction finders (RDF), frequency counters and near field detectors. FCC inspectors have the same clout as most law enforcement agencies when it comes to search, seizure and prosecution.

Yes, but this is a radio transmitters. I don't think the same regulations apply to transformers or inductive Owens. Different class of devices.

I found mention about broadband noise generators based on electric arc generators and zenner diodes. Could they be suited to have a small range?

 

 

Edited October 1, 2017 by Moreno

[Klaynos]

7 hours ago, Moreno said:

Yes, but this is a radio transmitters. I don't think the same regulations apply to transformers or inductive Owens. Different class of devices.

I found mention about broadband noise generators based on electric arc generators and zenner diodes. Could they be suited to have a small range?

 

 

In the UK electronic devices must not generate too much noise (there are very long technical documents on this). This is measured and tested for. Failure to comply will result in fines. 

50hz is less restricted as mains noise is difficult to avoid so people tend to take measures to work on this. 

Some frequencies in your band it is entirely illegal to transmit on by international agreement. No matter your intent or power. I know for a fact people are found doing this without their knowledge and fined. If your intent was to broadcast (even just the near field) the punishment would be substantially more. 

In the UK. Operating an RF jammer is illegal. Operating a device that transmits intentionally or above a very low level unintentionally across your band is illegal. Operating a spark gap is explicitly illegal. Most jurisdictions are likely to be similar. Given this I suggest reading rule 2.3 as this is moving close to the mark. 

[John Cuthber]

Even if there were no specific legislation about unlicensed transmitters, you would still be causing a nuisance* to whoever it is you are trying to jam.

That would get you sued.

It's also likely to annoy them and people with legitimate transmitters are often parts of organisations you don't want to annoy.

 

* in the legal sense
an act which is harmful or offensive to the public or a member of it and for which there is a legal remedy.

[Moreno]

On ‎30‎/‎09‎/‎2017 at 6:56 PM, Carrock said:

Without an aerial, a spark gap transmitter is mostly but not entirely near field; I doubt you could create a near field noise generator for 1 MHz - 10 GHz with a range close to 3m throughout the entire range without significant far field.

Can you give some approximate dimensions for a spark gap jammer in 900 MHz-5 GHz range? How much power will it consume to work efficiently in 3 meters range and how much noise will it produce in far field range and in what frequencies? What has to be done to make it work in GHz range? Probably spark pulses have to be extremely short and frequent? Or not necessary?

[Carrock]

31 minutes ago, Moreno said:

Can you give some approximate dimensions for a spark gap jammer in 900 MHz-5 GHz range? How much power will it consume to work efficiently in 3 meters range and how much noise will it produce in far field range and in what frequencies? What has to be done to make it work in GHz range? Probably spark pulses have to be extremely short and frequent? Or not necessary?

No. If you want to know why I gave you a -1 rep read the thread.

[Moreno]

What is the Faraday cage reliable frequency range of shielding? Can it shield from GHz range?

[Klaynos]

2 hours ago, Moreno said:

What is the Faraday cage reliable frequency range of shielding? Can it shield from GHz range?

A microwave shields GHz waves. So yes is the answer to your second question. The answer to your first depends on the configuration. 

We'd need to know your use case. 

[Moreno]

On ‎10‎/‎28‎/‎2017 at 5:11 AM, Klaynos said:

A microwave shields GHz waves. 

But far from completely?

[Klaynos]

1 hour ago, Moreno said:

But far from completely?

Define completely. The probability of an individual photon getting through will always be non-zero. It depends on your use case. For many an anti-static bag would suffice, others 3m of lead. 

[John Cuthber]

A sheet of cooking foil will shield microwaves "completely" for all practical purposes as long as it completely encloses the source (or detector).

It would be practiaclly opaque across the EM spectrum from low frequency RF all the way  up to soft Xrays

 

[Carrock]

8 hours ago, John Cuthber said:

On 28/10/2017 at 7:18 AM, Moreno said:

What is the Faraday cage reliable frequency range of shielding? Can it shield from GHz range?

 

 

On 28/10/2017 at 10:11 AM, Klaynos said:

A microwave shields GHz waves. So yes is the answer to your second question. The answer to your first depends on the configuration. 

We'd need to know your use case. 

 

8 hours ago, John Cuthber said:

A sheet of cooking foil will shield microwaves "completely" for all practical purposes as long as it completely encloses the source (or detector).

It would be practiaclly opaque across the EM spectrum from low frequency RF all the way  up to soft Xrays

 

These would shield in the sense of reducing microwave radiation to a (probably) safe level. Reducing the radiation to a level where it wouldn't be detectable by a nearby receiver would be a much bigger challenge.

Based on experience, if you attenuate a 20W transmitter by a factor of 1000 down to 20mW omnidirectional (not trivial), it can cause interference with a dipole receiver system 20 miles away. Much further with a directional receiver aerial.

10 hours ago, Klaynos said:

Define completely. The probability of an individual photon getting through will always be non-zero. It depends on your use case. For many an anti-static bag would suffice, others 3m of lead. 

Exactly.

 

[John Cuthber]

Hold a sheet of foil up to the light from the sun.

Can you see through it?

The eye will detect light over a range of something like 12 orders of magnitude.

If you can't see through the foil it's attenuation must be (at least) something like 1,000,000,000,000 fold.

Do you agree with my assessment that it is "for all practical purposes" opaque?

It's much more difficult to do the experiment at other wavelengths because we can't sense them directly.

Edited November 5, 2017 by John Cuthber

[Klaynos]

35 minutes ago, John Cuthber said:

Hold a sheet of foil up to the light from the sun.

Can you see through it?

The eye will detect light over a range of something like 12 orders of magnitude.

If you can't see through the foil it's attenuation must be (at least) something like 1,000,000,000,000 fold.

Do you agree with my assessment that it is "for all practical purposes" opaque?

It's much more difficult to do the experiment at other wavelengths because we can't sense them directly.

You need to be careful using the eye as a detector. It's nonlinear and will self calibrate to the ambient light level. Need to completely cover the eye (e.g. goggles). 

[John Cuthber]

If you wrap your head in foil you will verify that it gets dark.

[Klaynos]

21 minutes ago, John Cuthber said:

If you wrap your head in foil you will verify that it gets dark.

I agree entirely. And agree with the sentiment of your previous post. Eyes are just annoying optical instruments...

[Carrock]

2 hours ago, John Cuthber said:

Hold a sheet of foil up to the light from the sun.

Can you see through it?

The eye will detect light over a range of something like 12 orders of magnitude.

If you can't see through the foil it's attenuation must be (at least) something like 1,000,000,000,000 fold.

Do you agree with my assessment that it is "for all practical purposes" opaque?

It's much more difficult to do the experiment at other wavelengths because we can't sense them directly.

Note: Do not try this at home. Or at work. Or in a lab. Or in the ISS. Or...

 

Defeat the safety interlock on your microwave oven and open the door.

Hold a large sheet of cooking foil between your microwave oven and your eyes and switch on the oven.

The eyes are not very sensitive to microwaves and respond very slowly.

However after a few repeats your eyes will respond by developing cataracts.

On 04/11/2017 at 11:20 AM, John Cuthber said:

A sheet of cooking foil will shield microwaves "completely" for all practical purposes as long as it completely encloses the source (or detector).

It would be practiaclly opaque across the EM spectrum from low frequency RF all the way  up to soft Xrays

 

As it's not easy, if possible, to weld cooking foil, I assumed you meant wrap the source in cooking foil, which would leave gaps and enough leakage to detect the source at significant distance.

Even without gaps, this was the best commercial shielding foil I could readily find:

http://store.emfsolutions.ca/rf-shielding-foil/

Quote

Basic Interior Radio Frequency Shielding Protection - Extra sturdy Aluminum RF Shielding Foil -  Sold in 125 foot rolls, 4 ft wide. Blocks 99.999% of RF (micrwave) radiation (@2GHz)

You'd get a healthy 200microwatt signal from a 20watt shielded tx.

As the OP appears to want a short range illegal jammer, with a 3m near field for 3cm waves no less, enough leakage for his jammer to be detected by Homeland Security or whatever would not be acceptable.