Phone detector - not working for 4G

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?

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

Put it on vibrate and detect with an accelerometer?

--sp

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

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.

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

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? :-)

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

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.

Use a bluetooth ringer instead?

May get false positives in a machine shop.