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I have a receiver with sensitivity -50 dBm and an input signal from an antenna of -90 dBm, is it prudent to amplify the signal with a cascade of low-noise amplifiers? The LNA I found for my frequency band, 902-928 MHz, has a gain of 23 dB and NF 1.2dB, but it seems that I would need to amplify my signal by 50 dB to get an appropriate implementation margin for the receiver, requiring the use of multiple LNA's (or just amplifiers)

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That receiver sensitivity seems awfully poor to me, are you sure you're reading it right?

Based on this, you should add ~ 50 dB of gain to the front end. You should also add some filtering between the amplifier stages to make sure that out of band signals don't swamp the receiver.

The first stage will determine the total noise figure. If you have a 23 dB gain stage with 1.2 dB noise figure, that will set the total noise figure of the receiver at 1.4 to 1.6 dB. You should also look at linearity requirements, as there are paging networks at 928-932 MHz in the US that are running at pretty high powers.

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  • \$\begingroup\$ Can I add LNA's in series to provide 50 db of gain? \$\endgroup\$ – Vanush Vee Mar 18 '13 at 2:32
  • \$\begingroup\$ Yes, you can add LNA's in series to provide gain. You should put bandpass filters between LNA's to filter out unwanted signals as well. \$\endgroup\$ – rfdave Mar 18 '13 at 3:03
  • \$\begingroup\$ Watch out when using two LNAs - they can become unstable if correct or best practice PCB layout is not done. \$\endgroup\$ – Andy aka Mar 18 '13 at 8:43
  • \$\begingroup\$ You also have to be careful with the power supply. If you don't have adequate bypassing, then the supply lines can talk. \$\endgroup\$ – rfdave Mar 19 '13 at 3:00

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