(text in Serbian)

   50 MHz   70MHz   144 MHz   222MHz   432 MHz  1296 MHz

  50MHz      144MHz     432 MHz

   Preamp "in site" with ant. coax relay

Built by Saša, YU1EO

Built by Paja, ex YU2XO:      144MHz

Built by: Paja, ex YU2XO i Dragan, YU1GC  432 MHz

            144 MHz

144 & 432 MHz

Built by: Remco, PG0A and PF0A

Mechanical construction of amplifier box

DC inserter and attenuator

AutoCAD files in DWG format for Printed Circuit Boards:

BFP196 50 MHz - PCB    BFP196 70 MHz - PCB    BFP196 144 MHz - PCB

BFP196 222 MHz - PCB    BFP196 432 MHz - PCB    BFG540X 1296 MHz - PCB

All PCBs made of 1.6 mm double side FR4 or G10 epoxy (Er=4.8). Back side left as ground plane.

All used SMD components are type 1206.

AutoCAD files in DXF format for Printed Circuit Boards:

BFP196 50 MHz - DXF    BFP196 70 MHz - DXF    BFP196 144 MHz - DXF

BFP196 222 MHz - DXF    BFP196 432 MHz - DXF    BFG540X 1296 MHz - DXF

New!

Ultra Linear (High Dynamic) 

Low Noise Amplifiers

with improved input selectivity! (2003.)

better selectivity with new input circuit

-----------------

   50 MHz      144 MHz      432 MHz  

Built by: Mike, DL6IAK          144MHz

Built by: Steffen, DD0VF     144MHz

50 MHz

Built by: Alex, IK0VAQ

 http://ok1gth.nagano.cz/lnabfg540.pdf

Built by Tomáš, OK1GTH  for 144 & 432 MHz

* * *

Mechanical construction of amplifier box

DC inserter and attenuator

*****
How to tune preamp?

First trimmer to the antenna, Ct1, changing loading of second circuit and, as you can see on simulations pictures, change overall selectivity and NF, but it does not change resonant frequency. So there is no resonance peak when you tune Ct1! Second trimmer, Ct2, tune resonant frequency. Both trimmers influence to NF, but second trimmer, Ct2, keep good NF at new resonant frequency. First trimmer, Ct1, doesn't change resonant frequency, but change selectivity and NF very much!

Please, tune trimmer, Ct2, to best reception at frequency you want by listening some very weak signal. Then, trimmer Ct1 tune at same capacitance as first one. Both trimmers have to be close to calculated capacitance value given on schematic diagram if parasites of coils are not too big. Tuning is not very critical and by following suggested tuning procedure you will tune your preamp very close to minimum NF value! By this, all other calculated performances will be also achieved.


As illustration how tuning capacitances of Ct1 and Ct2 influenced gain and NF, I made some computer simulations on 70cm preamp.

           
You can see on pictures what happened with gain and NF when you change capacitances of one trimmer from its nominal value of 2.2pF (for 70cm band preamp), to 1.2pF and 3.2pF, while other one is kept at its optimum value of 2.2pF.

*****

AutoCAD files in DWG format for Printed Circuit Boards:

BFP196 50 IS - PCB       BFP196 144 IS  - PCB     BFP196 432 IS  - PCB   

All PCBs made of 1.6 mm double side FR4 or G10 epoxy (Er=4.8). Back side left as ground plane.

All used SMD components are type 1206.

AutoCAD files in DXF format for Printed Circuit Boards:

BFP196 50 IS - DXF        BFP196 144 IS - DXF      BFP196 432 IS - DXF   

Which amplifier is better for contests?

In order to check how amplifiers will behave in contests I conducted some simulations. GaAs FET MGF1302 and BJT BFP196 amplifier were fed with three strong signals ("three strong stations on 2m band") 7.1 mV (-30dBm) each, at its input. Results are given below, showing what would be heard with ideal, linear receiver (no receiver IMD!) under such conditions, and very obvious superiority of BFP196 preamplifier.

MGF1302 IMD test               BFP196 IMD test