Phone detector - not working for 4G

Hi

A friend needs a phone ringing detector for his workshop, as he cannot hear it when working with his machinery. The idea is easy - when the phone rings, like old TVs - you could hear it. I detect that and knows when something is happening. Then I turn on some light.

This works well for 3G, but 4G does not show.

Basically my 3G detector is a coil under the table, which goes to the base of a transistor. A similar schematic is here:

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However - 4G does not read out. I do get some 1-2 mV from the coil (up to 200mV from 3G)

Any ideas how I can react to 4G?

WBR Sonnich

Reply to
Sonnich Jensen
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The provider, maker, and model of the phone would be helpful. Not all phones are identical.

When the phone receives a call, the phone also goes into transmit to send back status info to the cell site. Most ring indicators detect this transmit RF. However, your device seems to be detecting the field produced by the speaker or rotary vibrator. I can't tell from your description. What does you coil look like and is it tuned to anything in particular?

4G is currently mostly data. You cell phone does not "ring" for an incoming data call. The exception is VoLTE (Voice Over LTE) which is currently available only on the higher end phones.

If your detector happens to be detecting transmit RF, it's helpful to know that 4G operates on different frequencies. See the chart at: for bands in use. You may need to adjust your pickup coil or use a better detector, especially if 4G for your unspecified carrier uses

2-3GHz.
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Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
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Reply to
Jeff Liebermann

Put it on vibrate and detect with an accelerometer?

--sp

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Spehro Pefhany 
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Reply to
Spehro Pefhany

Does the phone make any sound in headphones when it rings? If so, build a circuit that detects audio on the headphone jack. it might need some setting to be set, or a specific ringtone to get a strong signal on the headphone jack.

Jon

Reply to
Jon Elson

I'm guessing he's picking up the vibrator now, but the new phone has less field. He needs more gain. Or a better pickup coil.

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John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  
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Reply to
John Larkin

These things work on most cell phones. There must be some sort of Bluetooth standard for this sort of thing.

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Reply to
krw

On a sunny day (Tue, 27 Oct 2015 19:47:31 -0400) it happened Spehro Pefhany wrote in :

An old method was a photo detector that came on when the screen lighted up. LDR? :-)

Reply to
Jan Panteltje

No, that is not what I am doing.

When a (GSM and UTMS/G3?) phone rings, it first get a message from the mast. Next the phone will respond at high power to the mast, and the 2 of them will tell each other what the appropriate power levels should be. This is why electronics react to mobile phones before the ring. And this is what these systems are tracking. The transistor is needed as the diode B-E acts as a detector. As for 3G I can see from the signal whether it is a message or a call.

For 4G (LTE) it might be so, that the phone already know to use less power, and therefore I cannot detect it.

My current setup reacts before the phone rings and this is really useful for this thing - he will be at the other end of his workshop, and know the phone will be ringing in a second or 2 - which gives him a bit extra time to walk to the phone.

So, I am still looking for a way to detect activity from 4G phones.

WBR Sonnich

Reply to
Sonnich Jensen

OK, but a transistor b-e junction is not the best RF detector. BC547 is a slow amplifier, not an RF part. And L1 won't be a good antenna at RF frequencies.

I'm surprised that that circuit detects RF at all.

Reply to
John Larkin

Use a bluetooth ringer instead?

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Reply to
Jasen Betts

May get false positives in a machine shop.

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Reply to
Jasen Betts

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