Thursday, February 11, 2016

RX ANT Switching box, part 4 - High IP 40m Preamp with BPF

   There is my article about 40m preamplifier to new beverage box (click for all articles). It consists of BPF and notches for 160m and 80m, continue to switchable ATT (4dB) and switchable High IP preamp (click) with dual 2N5109 transistors. There is 3dB ATT and simple LC at the preamplifier output. Preamlifier is loaded with abt 7dB out of the band and with more than 25dB in band. Simple LC parts help to cut off unwanted signals at the preamp output. Look at measurement of that LC part.


cut off 160m 87 dB 96 dB
cut off 80m  80 dB 92 dB
cut off 20m  80 dB 88 dB
preamp gain 40m *, ** 13 dB  

* include BPF + output ATT ( 4dB ) + LC output filter - supply +15V and 2 x 80mA
** IP3 could be different than in past article because it is not widely loaded with perfect impedance

Insert loss of BPF is abt 1.78 dB with "poor" NP0 capacitors - have to try it with better ones.

BPF + notch 160/80 + ATT ON/OFF + preamp + ATT + out LC

Preamp with BPF / Preamp with BPF + 4dB out ATT + out LC (measureed with 30dB ATT, add +30dB) 

Preamp OFF / Preamp ON
Measured with FSL-6

Simple LC filter at the preamp output

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