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COMPARING DIFFERENT LNA of 144 MHz Band For Use in Noisy City

A low noise amplifier is important to the "WeakSignal" receiver for MS , far Tropo , EME !

      Low noise figure and High IP3 is easy to achieve with modern devices, but the large number of extremely high signal levels

  from BroadCast FM and TV stations - bigger and bigger problems nowadays !

  I was not quite satisfied with the IP3 of my old LNA, when running his in my noise QTH.

The "Old-School" LNA with Cavity

( use MGF1302, 1602, 1801, similar)

Not simple constructions, need tune, low noise, harrow band , big size...

LNA 144 MHz / MGF1302 / 10mA / NF < 0,5 db

The LNA with SPF-5122Z GaAs pHEMT MMIC from RFMD

Simple construction, no tune, low noise, wide band, high linearity, small size...

LNA 144 MHz / SPF5189z / 90mA / NF < 0,6 db/ High IP3

 

S21 without 4-stage helical band pass filter (only Cavity in front)

Measure has been with 10 db attenuator.

S21 with 4-stage helical band pass filter (only Cavity in front)

 

IP3 Measurements - about + 12 dbm

Resume: not best NF (0,55) , not good IP3 perfomance , Hmm... but this LNA have got me better result in my noisy city. I have got from my Yagi antenna summary power about -10 dbm (FM,TV BC station near my QTH).

Lets see equal LNA-box by PE1AHX and perfomance S21 or (zip)

S21 for LNA SPF5189z

(with 5 db ATT in Output of LNA)

SWR of input for optimal NF

 

IP3 Measurements - about + 26 dbm

Resume: Well, if you're only going to use this LNA for Contest and EME in Out of Town area - will be All Ok !

The FM BroadCast can be rejection is better than -60 dB below 135 MHz with 4-stage helical band pass filter , BUT only in output of LNA - then all strong signal will be in front of LNA !