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I am building a test rig for a device that has a GSM module to communicate and I want to test how the FW behaves when there is a comms loss and recovery. The GSM module of the device has an antenna connector where I can potentially tap into.

Just disconnecting the antenna doesn't work, because PCB traces some times are enough!

My thought was to have like a T connector and inject noise when I want to simulate loss of signal and then stop injecting to simulate a recovery.

What would be the easiest and most effective way to do this?

Note some devices use GPRS, others 2G, 3G or even 4G.

Edit just a note here, covering the device in some kind of Faraday cage is not possible. I am looking for an automated way of doing this.

Tomari
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    Remove the antenna, put the gadget inside an unplugged microwave oven. – JRE Mar 13 '21 at 09:56
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    If you really need to be sure the GSM is out, 2 minutes on high should do it. – K H Mar 13 '21 at 10:27
  • Moving the device is not possible, I am looking for an automated way of doing this. – Tomari Mar 14 '21 at 10:07
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    "Knock down" should probably be replied with a standard technical term such as "disable" for clarity. – Transistor Mar 14 '21 at 10:28
  • What does the word "automated" mean to you in this context? Done by robots? Controlled by computer? You need to explain your situation much more fully to get a better answer. – Elliot Alderson Mar 14 '21 at 12:47
  • Microcontroller being ebale to disable the network on command. – Tomari Mar 15 '21 at 11:10
  • How about a microcontroller that commands a linear actuator to lower a Faraday cage over the device? You still haven't explained why this is completely out of the question for you. I have a feeling there is something you don't want to tell us. – Elliot Alderson Mar 15 '21 at 11:59
  • You could have a Faraday cage on a solenoid or motor. To automate it. Or you could ground the antenna. – Passerby Mar 15 '21 at 14:53
  • Grounding the antenna, i will try this. What is it that i could possibly not want to tell you? Device could be as small as a 20x30x30 box but as big as 2m tall by 600 by 800 mm. cage must be lifted too high and it's just not convenient. – Tomari Mar 16 '21 at 12:12

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Buy a 10 bucks GSM/3G/4G radio jammer.

Cheap jammers have a range of 5 meters.

You should switch it on just for the time of your tests.

That's the fastest and cheapest way.

I did it in the past and it works.

To monitor if the comm port works, if the modem is alive and connected, just issue an AT+CSQ? every 12 hours.

Enrico Migliore
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    ..are those not illegal to buy and own? Setting up a signal to jam mobile signals is a bit questionable, even in a lab environment. How can you be sure that the jamming is localized and not jamming the phone of a passerby, perhaps even outside the building? Jamming would also trigger other failure modes than a loss of signal. – Arcatus Mar 15 '21 at 09:26
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    Thats the point, this is why I want to inject a signal i to the antenna cable, powerful enough to garbage the communication of the device but not the everyone else's – Tomari Mar 15 '21 at 11:11