LTC6431 Low IMD IF Amp

Recently, there was a bit of traffic on the EMRFD* Yahoo group about a new IF amp chip from Linear Technology: the LTC6431 ( The main interest in this device is its low intermodulation distortion (IM) as expressed by its third-order intercept point–in this case on the output (abbreviated as OIP3**): 47dBm OIP3 at 240MHz into a 50? Load. Its specified bandwidth is 20 to 1700MHz and it provides 15.5dB of power gain.

LTC6431_breakoutThomas Knutsen, LA3PNA, quickly designed up a breakout board for the LTC6431 and made it available at OSH Park for anyone to order ( I ordered a set of three for a mere $10.30USD. They were so cheap because OSH Park waits to fill a pcb panel with enough other boards to share the production costs. Once a panel is full, they run it and then distribute the boards to those who ordered them. It’s a great idea, and in this case it only took about ten days for the finished pcbs to show up in my mail. Their quality is excellent. This was my first experience with OSH Park, and I’m pretty pleased.

I haven’t populated the boards yet with LTC6431s, but once I do and play around with them, I’ll post an update.


*EMRFD stands for the title of Wes Hayward’s popular book, Experimental Methods for Radio Frequency Design, published by the ARRL. The Yahoo group is devoted to discussions based on the book and its design examples.

**See For a not-too-difficult discussion of IM, see Doug Smith, KF6DX, “Improved Dynamic-Range Testing” QEX July/August 2002 (