Re: Output Impedance?

Nick Kennedy
 

Well, I was following along with your reasoning and it made sense to me. From the diagram of the internals of the MMIC in the data sheet, it appeared the output is taken from the collector(s), so it made sense that the resistance would be determined by the external collector resistor.  But having a high return loss looking in does imply an inherent 50 ohm source resistance. Somehow(?)

The schematic I'm looking at is different.  I need some more versions. This one is Rev 6.06 of May 4, 2014. It does have an ERA-3+, but it has an RFC in series with the 270 ohm biasing resistor, essentially eliminating its effect on Rg. 

And the pi attenuator in this revision has resistances of 82, 93.1, 82 ohms, which will give 50 ohms looking in if there's a source resistance of 50 on the other end.

Oh - I see that it specifies values of 150, 39, 150 as a -6 dB option for the -12 dB attenuator shown.

73-

Nick, WA5BDU

On Sat, Aug 27, 2016 at 12:47 PM, mirasad314@... [PHSNA] <PHSNA@...> wrote:
 

Hi Nick sorry about that I checked my calc with S22=>21db

The impedance calculates to >48 Ohm. Which is great.
Sorry about that.
(  (270 || 50 ||150) +39  || 150)  = 48.61 ohms.  is the correct way.

Thanks
73



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