Cell phone LED

Discussion in 'General Electronics Chat' started by praondevou, Dec 7, 2011.

  1. praondevou

    Thread Starter AAC Fanatic!

    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.

  2. SgtWookie


    Jul 17, 2007
    I wasn't too keen on those things and was not sure why - look at what this guy had to say:
    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.
  3. praondevou

    Thread Starter AAC Fanatic!

    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".
  4. praondevou

    Thread Starter AAC Fanatic!

    Jul 9, 2011

    Just in case anyone had the same question. :) I just opened my old cellphone. It has a power amplifier inside that can provide 33dBm at 900MHz (2W).

    Wikipedia also has some info : http://en.wikipedia.org/wiki/DBm
  5. Jotto


    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.
    Last edited: Dec 8, 2011