[G0HZU_JMR]

The GMAX trace in my version of Genesys plots Max Available Gain when K>1 and it plots the theoretical Maximum Stable Gain (for K=1) if K is less than 1 on the graph. That's why it's always best to plot GMAX and K together in Genesys because each time K passes through 1 Genesys will produce the kinks in the GMAX curve as it hops between GMAX and MSG.

The equations are given in Genesys for both MAG and MSG.

I still think you should either experiment with JFET parts or maybe try a BJT in common base. Otherwise the BJT will produce too much power gain in common emitter and your VNA will overload the BJT and also port 2 of the VNA. See below for an s2p file of the SMD version of the MPSH10 BJT.

Despite what the authors of many RF theory books claim, a VHF BJT configured as a common base amplifier is very prone to instability. This instability can happen well above 1GHz.

In common emitter the MMBTH10 can go unstable up to about 2.7GHz at 10vce and 10mA according to my VNA data although this assumes lossless resonator components. In reality 2.4GHz would be a more realistic upper limit for oscillation assuming real components were used to make up the oscillator circuit.

A 2N3904 at a similar bias point can perform a similar oscillation trick up to about 1GHz. The GMAX and K data from my VNA show that the 2N3904 can achieve about 15dB power gain at 145MHz with K>1 at 10Vce and 10mA Ic.
This is based on my VNA data from an On-Semi 2N3904 bought from Farnell recently. Ideally you should buy from Farnell (or similar) if you want genuine On-Semi parts to compare against.

Have a play with the common base s2p model below using Genesys. You should be able to plot GMAX and K.


! Filename: MBTH10CA.S2P Version: 3.0
! Philips part #: PMBTH10 Date: Dec 1990
! Bias condition: Vce=10V, Ic=5mA
! CB CONFIGURATION
# MHz S MA R 50
! Freq S11 S21 S12 S22
40 .775 176.8 1.757 -3.6 .002 85.3 .988 -1.0
100 .769 172.4 1.750 -8.7 .006 95.1 .992 -2.5
200 .751 165.3 1.727 -17.4 .012 99.7 1.004 -4.7
300 .729 158.7 1.689 -25.9 .019 107.0 1.017 -6.8
400 .703 152.6 1.642 -34.4 .027 108.7 1.031 -8.8
500 .675 147.2 1.591 -42.6 .035 108.2 1.040 -10.8
600 .650 142.4 1.535 -50.8 .045 107.7 1.045 -13.1
700 .626 138.1 1.473 -58.8 .055 106.8 1.046 -15.7
800 .607 134.2 1.403 -66.9 .065 105.5 1.045 -18.7
900 .587 130.7 1.338 -74.8 .077 104.8 1.044 -22.0
1000 .571 127.4 1.274 -82.8 .088 103.8 1.045 -25.5