Cell phone LED

Thread Starter


Joined Jul 9, 2011

1. I'm trying to find a product. It is a small device you could put on a cellphones antenna. A LED inside the device would light up when the phone was transmitting. I think it was related to RF energy captured from the cellphone transmitter.

I'm trying to find it but was not so lucky until now.

Anyone has the right name of this thing?

2. I try to find a reliable source of information about transmitting power used for the different frequencies (mainly GSM), i.e. the EIRP coming from the cellphone. All I find is sites talking about to health issues which is not what I'm looking for.



Joined Jul 17, 2007
I wasn't too keen on those things and was not sure why - look at what this guy had to say:
The Led is direct drive by the RF energy in the Antenna, and these things are very sore subject in the regulatory community. The LED on the end is a highly non-linear device, and as a result, produces a significant amount of spurious radiation at frequencies that only pollute the airwaves. The duty cycle is pretty short (217 times a second)for a total of 12.5% of the elapsed time.
I figure that any energy being used for anything besides sending/receiving a call is pretty much a waste of power.

BTW, I Googled: 'LED cell antenna' to find that thread, and many other hits.

Thread Starter


Joined Jul 9, 2011
I wasn't too keen neither, but I know why. I found it was totally unnecessary.:)

Yes, it is a waste of power and probably causing negative effects because it's in the (very) near field of the antenna and therefore also has an effect on the antenna, you are are right.

I don't even know why it popped up in my mind, because the background of what I'm looking for is not a receiver in the near field but a RF-powered RFID tag in the far field. I was wondering if a GSM cellphone could be used as RF-power source in some way. A few Watts would be necessary, commercially available readers have about 3W.

That's why I asked about the transmitting power of GSM cellphones...

Btw, of course when using GOOGLE it's all about using the right search terms. I finally found it under "flashing antenna".


Joined Apr 1, 2011
We use a neon bulb to test for RF. I also think we were putting a bit more power. I would use the blub on a plastic stick to test radar and radios.

You don't really attach the bulb to the unit, just let it sit next to it. I am not sure how 2 watts would make the lamp look, since I deal with a bit more power then that. I would think you would get something, but not sure you would be able to see it at that low of power.
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