A near field RF jammer?

[John Cuthber]

"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."
Overlapping the joints + crimping them would work fine.

If this is right

http://www.spectralcalc.com/blackbody_calculator/blackbody.php

then I think I emmit more than 200 µw of microwave radiation.

It may be instructive to wrap your mobile phone in foil carefully, then try to call it.

A bit of bubble wrap round the  'phone first might be a good idea.

 

[Klaynos]

39 minutes ago, Carrock said:

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.

I had assumed the shield was instead of a jammer, not to limit its range. The jammer would still be illegal in many jurisdictions. 

[Carrock]

1 hour ago, John Cuthber said:

"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."
Overlapping the joints + crimping them would work fine.

If this is right

http://www.spectralcalc.com/blackbody_calculator/blackbody.php

then I think I emmit more than 200 µw of microwave radiation.

It may be instructive to wrap your mobile phone in foil carefully, then try to call it.

A bit of bubble wrap round the  'phone first might be a good idea.

 

"Overlapping the joints + crimping them would work fine."

As you don't mention it I assume you accept that 50dB attenuation figure I gave for commercial aluminum RF shielding foil which makes the above moot.

 

"It may be instructive to wrap your mobile phone in foil carefully, then try to call it."

A 20 mW or so signal from a low gain aerial on a tower attenuated to (far less than) 200nw (because of the distance) for an inefficient mobile phone aerial isn't equivalent to e.g. a 200µw signal near a radar dish trying to distinguish between that signal and a reflected signal from an ICBM 200 miles away.

"then I think I emmit more than 200 µw of microwave radiation."

Yes; broadband radiation.

I thought it was clear I was talking about narrow band radiation, like with a mobile phone.

If we compare like with like, the 200µW leakage from the 20W tx might have a bandwidth of 1KHz. If you emit 200 µw of radiation over the range 300 MHz to 300 GHz that would on average be around 10exp-17W in each 1KHz band.

 

[John Cuthber]

I'm a broad band emitter- and a broad band absorbed too. So, to me, it doesn't matter much if I'm "irradiated" by 200µW of narrow or broad band radiation.
It won't do me any harm.

 

I never checked the RF attenuation of a layer of foil. 50Bd might be a cautious value (or even a guess). 99.999% will convince most people it works.

This page which cites  over 100 dB reductions might be just as valid.
http://www.slt.co/products/RFShieldingFoil/RFShieldingFoil.aspx

 

The "phone in a wrapper is probably the best "measurement" I could do

Edited November 5, 2017 by John Cuthber

[Carrock]

2 hours ago, John Cuthber said:

I'm a broad band emitter- and a broad band absorbed too. So, to me, it doesn't matter much if I'm "irradiated" by 200µW of narrow or broad band radiation.
It won't do me any harm.

 

I never checked the RF attenuation of a layer of foil. 50Bd might be a cautious value (or even a guess). 99.999% will convince most people it works.

This page which cites  over 100 dB reductions might be just as valid.
http://www.slt.co/products/RFShieldingFoil/RFShieldingFoil.aspx

 

The "phone in a wrapper is probably the best "measurement" I could do

Straw man arguments.

 

[John Cuthber]

29 minutes ago, Carrock said:

Straw man arguments.

 

What do you consider "straw man" to mean?

[Carrock]

19 minutes ago, John Cuthber said:

What do you consider "straw man" to mean?

Quote

I'm a broad band emitter- and a broad band absorbed too. So, to me, it doesn't matter much if I'm "irradiated" by 200µW of narrow or broad band radiation.
It won't do me any harm.

No one on this thread has suggested 200µW of microwave radiation will do any harm (unless the authorities track down the jammer).

One straw man.

Quote

I never checked the RF attenuation of a layer of foil. 50Bd might be a cautious value (or even a guess). 99.999% will convince most people it works.

Actually an appeal to idiocy. In the example I gave, that would allow about 200µW through. A pretty basic narrowband receiver needs about 1pW input.

And what is a Bd?

 

Quote

This page which cites  over 100 dB reductions might be just as valid.
http://www.slt.co/products/RFShieldingFoil/RFShieldingFoil.aspx

Costs about 20 or 30 cents/square foot and is apparently about 11mm thick. I doubt from its attenuation graph that it's just a sheet of thin kitchen foil in a fancy wrapping so not like for like.

I notice the advert has "approximately," without error limits or a guaranteed minimum.

Quote

The "phone in a wrapper is probably the best "measurement" I could do

An experiment using less than a millionth of the required power at the rx, with an entirely predictable result.

You might as well wave a wrist watch in front of your face to prove relativity wrong.

So only one straw man.

 

 

 

[John Cuthber]

 

1 hour ago, Carrock said:

No one on this thread has suggested 200µW of microwave radiation will do any harm

You described it as healthy- I presumed you were being ironic, rather than meaningless.

9 hours ago, Carrock said:

You'd get a healthy 200 microwatt signal

1 hour ago, Carrock said:

And what is a Bd?

A transposition error

 

 

1 hour ago, Carrock said:

So only one straw man.

Nope, not even 1

1 hour ago, Carrock said:

Costs about 20 or 30 cents/square foot and is apparently about 11mm thick. I doubt from its attenuation graph that it's just a sheet of thin kitchen foil in a fancy wrapping so not like for like.

If you think that something made from aluminium 11 mm thick can be rolled up into rolls 125 feet long and 4 feet wide  (but with the rolls weighing 21 pounds then- lets just say you are not on this planet.
The thickness is specified as 11 mil- which is  heavy duty for cooking for cooking foil, but not nigh half an inch as you suggested.

 

https://www.ebay.com/p/Nashua-Aluminum-Foil-Tape-for-Waterproofing-Repair-48-Mm-Width-11-Mil-Thick/682240054?iid=322854283848

This is the sort of stuff that's 11 mil thick

Edited November 5, 2017 by John Cuthber