ATF54143 Preamplifiers Articles Removing
24. December 2002.
I decided to remove ATF54143 preamp articles because some measurement
on built amplifiers didn't confirmed predicted performances.
In this very moment nobody knows what reason for these big discrepancies is
(NF is higher about 1.5dB) because all professional programs for calculations
and simulations ( Ansoft Serenade v8.71, Agilent ADS2001 and Eagleware
Genesys v8.01) agree that everything is OK, but in practice something
I am suspicious that transistors are not uniform and from one to
another specimen differs very much. But I am not sure, of course!
Until that we found what is problem, I decided to remove article from my
Strongly recommended modification
19. January 2003.
Finally we discovered (thanks to S53WW and other S5 guys) problem of higher
than expected NF of YU1AW ATF54143 preamps.
The problem was in poor quality of 22uH RFC in gate bias!
This RFC, on such high frequencies, serves as poor quality capacitor and
produces much higher preamp NF than expected!
Cure is very simple. Instead of mentioned RFC should be used air coil with
first parallel resonance near working frequency of preamp.
Added coil must be orientated at right angle to printed circuit coil in
drain line to minimize parasitic input-output coupling effects and
1. Remove resistor of 5.6 ohms (33 ohms in 2m preamps), capacitor of 0.5 pF and 22uH choke in gate bias line.
2. Replace them with series connected coil RFC and resistor R as follows:
RFC coil data:
coil inner diameter D=3mm
coil length l=2mm
turns number n=6 turns (close wounded)
wire diameter dw=0.3-0.35mm enameled
resistor in series with coil R=56 ohms
n=11 turns (close wounded)
n=30 zav. (close wounded)
After this, strongly recommended, modification measured NF were very
close to predicted!
Gain and IP3 were almost exactly as predicted!
NF and Gain measurements:
(the best results)
144MHz: NF=0.4dB, Gain=26dB (measured by YU1AW)
144MHz: NF=0.37dB, Gain=20.8dB (measured by OK1UOW)
432MHz: NF=0.38dB, Gain 22dB, P1dB=18dBm (measured by S53WW)
1296MHz: NF=0.4dB, Gain=17.7dB (measured by S53WW)
73, Dragan YU1AW