GSM and amplifiers

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povidanius
Posts: 2
Joined: Fri Oct 06, 2017 9:29 am

GSM and amplifiers

Post by povidanius » Thu Nov 16, 2017 1:24 pm

Hi all,

I am new to radio stuff, and would be grateful if somebody clarify me some points. Lets say, my objective is to extend range of bladerf&YateBTS -based GSM base station.

1. In order to expand bladerf range (e.g. in GSM application) LNA should be connected to RX, and power amplifier (PA) to TX? Maybe somebody could recommend some LNA and PA hardware for GSM (e.g. to cover 50-100 m radius)?
2. After adding LNA and power amplifier the board should be recalibrated?

My experience is the following. YateBTS works good ot out the box (but the range is only few meters). When I connected PA to TX and LNA to RX, GSM network is not detected by handset. Afterwards, when plugging antennas to RX and TX directly, GSM networks is still not detected. After recalibration of bladerf GSM again appeared.

bglod
Posts: 127
Joined: Thu Jun 18, 2015 6:10 pm

Re: GSM and amplifiers

Post by bglod » Fri Dec 01, 2017 2:19 pm

Be aware that the bladeRF should not be exposed to signals greater than +23 dBm as this will damage the RF front end. The ADC saturates at a much lower input power -- around -13 dBm. Your issue with the amplifier could be that the signals are too strong and therefore are clipping either at the handset or the bladeRF. You can test this by moving (much) further away, and/or turning down the gains of the bladeRF. You could also try using Gqrx or gr-fosphor to view the spectrum to see if any clipping is taking place.

If you find clipping to be the issue, you can grab an RF limiter device that will attenuate strong signals without impacting your ability to receive lower power signals.

The LMS calibration routines do not take into consideration any external components, so I would not have expected a recal to have corrected the issue.
Electrical Engineer
Nuand, LLC.

povidanius
Posts: 2
Joined: Fri Oct 06, 2017 9:29 am

Re: GSM and amplifiers

Post by povidanius » Fri Feb 09, 2018 10:20 am

Thank you for advice. I was able to extend range of GSM base station to 50-100 meters with quite stable signal, which is enough for my application.

bglod
Posts: 127
Joined: Thu Jun 18, 2015 6:10 pm

Re: GSM and amplifiers

Post by bglod » Fri Feb 09, 2018 11:51 am

Excellent! Was it saturation that was causing the problem, or was it something else? (In case someone with a similar issue comes across this post).
Electrical Engineer
Nuand, LLC.

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