cell phone harmonics in lbw while xmiting from inside the dome.


    People have been asking how cell phones transmissions affect observations done on the telescope. To get an unambiguous signal,  cell phone transmissions were done from inside the dome (on the stairwell leading into the turret floor).


Data processing:

    Data from the first 90 seconds (when there was no cell phone transmission) were used for a bandpass correction. The processing was:

Plotting the data:

    The plots show the cell interference in the lbw receiver.


    The allocated cell phone bands are: We must be seeing the second harmonic of the 824-849 uplink. The cell phone is actually transmitting on: The lbw wave guide will not let 800 Mhz enter the dewar, so the harmonics must be coming from the phone itself.

    The frequency bin width of 400 Khz at the second harmonic becomes 200 kHz at the fundamental. This is the channel width of the GSM format. The range 826 to 833 must be the  frequency channels allocated to the tower that the phone was talking to. The 6 channels at 845 to 846 look like the 5 common control channels that are used for control.  Gsm does a frequency hop as well as tdma. Some  of the time variation in a channel is from that.  The output power is also regulated depending on  how much talking is being done.

    The individual 1 second spectra show max levels of 1.5 times Tsys (about 25K*1.5). The peak value is larger than this since the device does not transmit continuously in 1 freq channel.

    These harmonics lie on top of the 1665/1667 OH line. Next thing is to see if we can see any  harmonics when transmitting from the visitor center.

    You can see more gsm info here.

processing: x101/050819/cellph.pro