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In- output impedance 2SC1971 - RF Cafe Forums

Because of the high maintenance needed to monitor and filter spammers from the RF Cafe Forums, I decided that it would be best to just archive the pages to make all the good information posted in the past available for review. It is unfortunate that the scumbags of the world ruin an otherwise useful venue for people wanting to exchanged useful ideas and views. It seems that the more formal social media like Facebook pretty much dominate this kind of venue anymore anyway, so if you would like to post something on RF Cafe's Facebook page, please do.

Below are all of the forum threads, including all the responses to the original posts.

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!

Posted  11/12/2012
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