morning

Hey guys I don't know if any of you might be able to help answer this:

were is everyone???

@EwokNightmares heya

@MLM hi

@jippie How come that was funny?

kickstarter.com/projects/technicalillusions/…

Bonjour

@ThePhoton Günaydın

@abdullahkahraman Just like Flickr! "Now you know how to say "hello" in Turkish!"

Unless you actually just called me a jerk or something.

@ThePhoton Actually that is "Good morning" in Turkish :)

hrm... it seems that I still have some work to do on my antique radio that I'm restoring... the rectifier tube flashes blue at turn-on =\

Flickr finally got a better user interface..

but it receives radio stations!

@W5VO Wow, I never do anything.. I just browse the internet..

It's been ages since I've soldered something..

well, that radio was a motivator to just browse the internet - all the internal wiring used rubber wire... that was rotting

sorta like this:

Ugh

no kidding

I got all the audio stuff through to the 1st IF, but I'm going to hope that I don't need to do the RF deck... that would probably mean a full disassembly

I don't know anything about RF, but have a nice repair!

@abdullahkahraman It's nothing about the RF part... it's just a lot of tight wiring

tricky to get an iron in there to fix things

@W5VO Friend of mine has an ancient pinball machine... not quite working... crazy amounts of cloth-insulated wire in there.

@W5VO What is the frequency that is in this thing? How could they get by wiring? Is the case a big chunk of ground?

@ThePhoton Oh man, I can't imagine rewiring a pinball machine and staying sane

@abdullahkahraman hrm... it's 3-bands, up to maybe 10-15MHz

and yes the deck is a huge copper ground

@ThePhoton programmer.97things.oreilly.com/wiki/images/4/44/Sdm-big.jpg

got my book on friday and saw this on the back

@EwokNightmares Looks like you got the right book.

@W5VO so sad :(

@ThePhoton guessing he did not get a new edition haircut for his new edition book

@EwokNightmares That haircut was looking dated when the book came out originally

Does anyone know if the Forward Transconductance on a MOSFET datasheet is the same parameter (gm) discussed in textbooks? The units don't agree.

Units of transconductance might be A/V, mhos, or siemens, which all mean the same thing.

A Fairchild 2N7000

Thats what I thought too, the book gives Transconductance as A/V^2

@atomSmasher That's not right. Can you show the context in the book? Could they be talking about the change in transconductance with changing gate voltage or something?

Sure! I am looking at Microelectronics : Circuit Analysis and Design by Neaman. The gm I am referring to is used in the textbook to determine small signal gain. ie Av = -gm(ro||Rd) = Vo/Vi. gm is derived as 2*(Kn*Idq)^1/2

I constructed a common source circuit on a breadboard and the math works, but the units don't make sense!!

I am going to chalk it up to a typo!

@ThePhoton One last question, and this might be a little far fetched, do you know if its possible to obtain (know of any good sources), or derive a MOSFETs channel width, length, and oxide thicknesses based on the values given on a datasheet? I am trying to create an accurate spice model.

How come no one left this except me?

;P

@atomSmasher I don't think that's possible. For one thing, the main dependence is W/L, so I doubt you can get independent values for W and L. Also, things like parasitic resistances and lead inductances often have a bigger effect than the FET structure itself. Better to look for a vendor who provides decent SPICE models.

For example, Fairchild has a 2n7000 model available if you make an account on their website.