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## Re: [Amps] Understanding S Parameters

 To: Re: [Amps] Understanding S Parameters "Carel, pc5m" pc5m@xs4all.nl Tue, 16 Jun 2015 22:45:08 +0200 mailto:amps@contesting.com>
 ```Hi Drax, If S11 > 1 it means it is not unconditional stable, i.e. it might oscillate... Your formula for input impedance is only valid if s12 or s21 = 0, and I think that is not the case. Otherwise: Gamma(Inp)=S11+(S12*S21*Gamma(outp))/(1-S22*Gamma(outp)) 73's Carel. -----Original Message----- From: Amps [mailto:amps-bounces@contesting.com] On Behalf Of Drax Felton Sent: dinsdag 16 juni 2015 21:53 To: amps@contesting.com Subject: [Amps] Understanding S Parameters I am trying to understand S Parameters for a RD00HHS1 transistor. The S11 parameters listed in the datasheet are as follows: 10 MHz 1.002 (mag) -3.6(ang) 30 MHz 1.003 -9.9 50 MHz 1.005 -16.8 100 1.007 -33.5 150 0.989 -49.8 I'm trying to estimate the input impedance at 0.475MHz. But I am uncertain what it means when the mag is greater than 0.999. Using the 10 MHz S11 value because it's available I get: Gamma = 1.002 = (ZL-50)/(ZL+50) --> ZL= -50050 ohm impedance or a VSWR of negative 1001:1. What am I doing wrong? What does this mean? My other attempts at calculating input Z also result in negative impedances in linear form like -50.58-1589j My RF books do not seem to say anything about this. Kb3x _______________________________________________ Amps mailing list Amps@contesting.com http://lists.contesting.com/mailman/listinfo/amps _______________________________________________ Amps mailing list Amps@contesting.com http://lists.contesting.com/mailman/listinfo/amps ```
 Current Thread [Amps] Understanding S Parameters, Drax Felton Re: [Amps] Understanding S Parameters, Carel, pc5m <= Re: [Amps] Understanding S Parameters, Markku Oksanen Re: [Amps] Understanding S Parameters, Saandy Eban Re: [Amps] Understanding S Parameters, Drax Felton Re: [Amps] Understanding S Parameters, Steve Thompson