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In- output impedance 2SC1971 - RF Cafe Forums

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Post subject: In- output impedance 2SC1971 Posted: Sun Feb 04, 2007 3:17 pm


Joined: Sun Feb 04, 2007 2:58 pm
Posts: 9
Hello all,

Just found this forum...very nice.
For a week now i try to understand the wonder world of micro-strips.
This in combination with the 2SC1971 transistor.
I try a lot in RF-SIM99,and it works fine.
I just take a few ohm's for the in- and output impedance.
But now i want to try some for real,but i can't find the data for the transistor.
How do i get the correct impedance from the sheet for appr. 100MHz
And what would be a acceptabe reflection(dB) for wideband use.
I can get from the simulations a reflection of maximun -22dB from 88-108MHz...isthis acceptabe.
I hope to get some info from one of you

Greetings Bert


Post subject: 2sc1971Posted: Mon Feb 05, 2007 5:34 pm


Joined: Wed Feb 22, 2006 3:51 pm
Posts: 104
The 2SC1971 data sheet is particularly sparse - I don't think there's enough information on the copy I found on the web to allow you to use it in a simulator.

It appears that the device has ceased being manufactured - do you have a particular reason to use that specific device?

Good Luck,


Post subject: Posted: Tue Feb 06, 2007 4:39 pm

Site Admin

Joined: Mon Jun 27, 2005 2:02 pm
Posts: 373
Location: Germany
I also looked at the data sheet of this transistor and the main information is missing i.e. the S-Paramaters.

Therefore, you can't tell what is the input or output impedance in relation to the frequency. I suggest you to contact the manufacturer and ask for this data or use an alternative device which has a data sheet in which S-Parmaters are included.

Good luck!


Post subject: Posted: Tue Feb 06, 2007 6:30 pm


Joined: Sun Feb 04, 2007 2:58 pm
Posts: 9
Thanks for the reply's guys.
The original 2SC1971 from mitshubishi is no more in production.
The ones now being sold are chinese reproductions,but work just as good.
I made a design by copying some pieces of the www and adapt the strips some,until it was as good as flat from 88-108MHz.
And this on single side board???
Maybe they don't work as a microstrip,but as a low Q coil.
But my goal was to understand the strips,and make whatever i want.
And match one transistor to the other,without going to 50ohm again.
I have a long way to go


Post subject: microstrip?Posted: Tue Feb 06, 2007 8:55 pm


Joined: Wed Feb 22, 2006 3:51 pm
Posts: 104

Just a remark, so that you don't go charging off down the wrong path...

Microstrip is defined as a strip of conductor above a ground plane, separated by a dielectric. So there is no such thing as microstrip on a single-sided board. I'm not sure if what you have would be classified as CPW (co-planar waveguide) or not - I've never done CPW.

The equations in the books for microstrip won't do the job for you.

Good Luck!

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