EEVblog Electronics Community Forum

Electronics => RF, Microwave, Ham Radio => Topic started by: Jane on June 12, 2017, 06:02:10 pm

Title: What kind of LNA transistor to use?
Post by: Jane on June 12, 2017, 06:02:10 pm
I have a satellite tuner where an input transistor needs to be replaced. It is SMD transistor so it has only a marking code such as GT.
It has 4 pins( probably 2 emitters).
Can anyone suggest a transistor that can be a suitable for the replacement?
Thank you
Title: Re: What kind of LNA transistor to use?
Post by: rfeecs on June 12, 2017, 06:21:43 pm
That's not a lot of information.  Typical 12GHz satellite receiver uses low noise HEMT.  Something like this:
http://www.cel.com/pdf/datasheets/CE3512K2.pdf (http://www.cel.com/pdf/datasheets/CE3512K2.pdf)
Title: Re: What kind of LNA transistor to use?
Post by: Jane on June 12, 2017, 07:55:09 pm
Thanks for your reply.
In my tuner there is a transistor ( of a shape ) like this
http://www.nxp.com/documents/data_sheet/BFG425W.pdf (http://www.nxp.com/documents/data_sheet/BFG425W.pdf)

But not sure if that kind transistor can be used.
Does anyone know?
Title: Re: What kind of LNA transistor to use?
Post by: KE5FX on June 12, 2017, 08:24:30 pm
Can you post a reasonably-detailed photo of the area of the PCB surrounding the part you need to replace?  That might provide some clues.

Unfortunately a lot of those discrete microwave transistors are no longer available.  NXP in particular has killed a lot of nice parts over the past few years. 
Title: Re: What kind of LNA transistor to use?
Post by: rfeecs on June 12, 2017, 08:57:56 pm
Quote from: Jane on June 12, 2017, 07:55:09 pm
Thanks for your reply.
In my tuner there is a transistor ( of a shape ) like this
http://www.nxp.com/documents/data_sheet/BFG425W.pdf (http://www.nxp.com/documents/data_sheet/BFG425W.pdf)

But not sure if that kind transistor can be used.
Does anyone know?
Well that's a different package, an SOT-343.  Still doesn't say much.
If it really is an LNA, it's more likely to be a HEMT.  Definitely not interchangeable with a bipolar.
NEC(CEL) and Mitsubishi are common manufacturers.
Here's another one in an SOT-343 compatible package:
http://www.cel.com/pdf/datasheets/CE3514M4.pdf (http://www.cel.com/pdf/datasheets/CE3514M4.pdf)
Title: Re: What kind of LNA transistor to use?
Post by: chrisl on June 13, 2017, 03:59:36 am
post some pics so we can see the part.
CE3514M4 from CEL or MGF4937AM from Mitsubish may fit the package description.
However, you cannot just drop in an alternate part and expect it to work at this frequency.
 
Title: Re: What kind of LNA transistor to use?
Post by: Jane on June 13, 2017, 02:33:07 pm
Here is a picture of the tuner and I marked by red arrow the transistor.
Thanks for help
Title: Re: What kind of LNA transistor to use?
Post by: BigBoss on June 13, 2017, 06:06:26 pm
What is the SMD marking on the transistor ?? It might still be available.
Title: Re: What kind of LNA transistor to use?
Post by: Jane on June 14, 2017, 07:54:44 am
In the original tuner made by ALPS the  marking is  IYU  while in a clone tuner made by Earda Electronics Ltd( brand  Eardatek) is  marking GT.

Any idea how to source that transistor?
Thanks

Title: Re: What kind of LNA transistor to use?
Post by: Gribo on June 14, 2017, 02:16:14 pm
Try looking for the Conexant reference design.
This transistor is connected to a type F connector, I don't think it is a 25GHz part. Usually, the LNB is located near the dish.
Title: Re: What kind of LNA transistor to use?
Post by: PA0PBZ on June 14, 2017, 05:32:52 pm
No, this is not an LNA or LNB, it's the tuner where the LNB connect to and it works roughly from 1-2GHz.
Title: Re: What kind of LNA transistor to use?
Post by: chrisl on June 14, 2017, 07:40:51 pm
Looks like L-band stuff.  No Ku  or X for sure.
Title: Re: What kind of LNA transistor to use?
Post by: Jane on June 16, 2017, 05:41:11 pm
No, not  for Ku band, but how can I find an equivalent?