TRANSFORMING A LNB INTO A LNA

(2014-11-04)

Preface

Low Noise Blocks (LNB) are easily transformed into Low Noise Amplifiers (LNA). In this brief article I am going to show the procedure I used to do such conversion using an old Amstrad LNB.

FIGURE 1: LNB WITH THE COVER REMOVED

FIGURE 2: SHIELDING PART REMOVED

FIGURE 3: LNB PCB

After both antenna probes, two Low noise GaAs FETs marked with purple colour and a dot. Signal is combined using a Wilkinson combiner. 

 NEC FHX14LG
 Gain: 13dB
 NF: 0.55dB
 Ptot: 180mW

After Wilkinson combiner, one Low noise GaAs FET marked with orange colour and a two dots. 

 NEC FHX06LG
 Gain: 10.5dB
 NF: 1.1dB
 Ptot: 180mW
FIGURE 4: LNB PCB REMOVED

FIGURE 5: SOLDERING A 0603 SIZE 1pF SMD DC BLOCKING CAPACITOR AT TRANSISTOR GATE
ANTENNA PROBE IS REMOVED

FIGURE 6: PCB IS CUT WITH SCISSORS AND A SMA FEMALE CONNECTOR IS SOLDERED IN PLACE

FIGURE 7: AFTER ANOTHER SCISSORS CUT, A SMA FEMALE CONNECTOR IS SOLDERED AT FILTER OUTPUT.
BIAS FOR UNUSED GaAs FET IS REROUTED USING A PIECE OF CABLE

Testing

FIGURE 8: 10MHz-20GHz SWEEP WITH MARCONI 6200 MICROWAVE TEST SET. S21 PARAMETER.

FIGURE 9: 8GHz-13GHz SWEEP. MAX GAIN IS 20 dB AT 11.2 GHz. 11.87 dB AT 10.368 GHz

FIGURE 10: PLACING A PIECE OF TAPE OVER THE FILTER DECREASE FREQUENCY RESPONSE

FIGURE 11: FILTER BANDPASS WENT DOWN AFTER PLACING THE TAPE. LOSSES INCREASED.

Bibliography

LNB and its radio usage, Miguel A. Vallejo, EA4EOZ
Sheffield Microwave round-table 2008 
  Copyright (c)  2013 Ramiro Aceves .
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