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Showing posts from April 5, 2018

SPF5189z Low noise preamp 23cm

14-4-2018 updated


Above the low noise  preamp 50 - 4GHz    ebay  6€

Tested  2 small porto antennas
1 Baofeng UV antenna left   2nd best signal on PI2NOS
2 eBay DIAMONDSRH805S  wide band 144/432/1200  it works for its size as expected
3 piece of wire :   best signal in the setup...

Unit under test at workbench.
It was stable  50mA  at 5V   few days,  but sudden the current went up to 100mA
And i could  no longer adjust it with the negative bias Voltage.
The - Voltage went to zero and the SPF input port became low Z.
This SPF5189z was broken  no oscillations, no input overload just it broke while i was receiving the PI2NOS 430.125 using a small antenna at the workbench.

The specs of  SPF5189z  say it has an internal circuit  regulating the bias current.
Replaced . again   with an other of the 5 spare SPF i have.
The new one again could be adjusted at 50mA  5V 
The current raises to 150mA  when removing the  negative gate voltage.
Where is that internal bias circuit ?
I suspect  eBay …