[HomeBrew] 2N2222A-2N3904 question

[jkearman at att.net [Jim, KR1S]]

> Since the highest frequency in the circuit will be 2.00MHz, the PRIMARY 
> consideration is noise figure which the NTE book doesn't give. Is the 
> 3904 "quieter" than the 2222A or is it a moot point? 

I can't imagine why you'd be concerned with NF at 2 MHz. Even at a quiet location with a quiet antenna like a loop, the atmospheric noise would exceed the NF of the front end. According to my Philips datasheet for the 2N2222A, the NF is 4 dB at _200 MHz_. For the 3904 (Fairchild) it's 5 dB, however, NF for the 2222A is specified at 200 uA Ic, and 100 uA Ic for the 3904. If you want a bulletproof active front end you might consider the 2N5109, with a specified NF of 3.5 dB at _10 mA_ Ic. Ocean State Electronics lists the 2N5109 but they may be selling an NTE version. Biasing a Class A amplifier isn't hard; Solid State Design explains how. You might also look at the biasing for post-mixer amplifiers using the 2N5109, like the 40-meter rig described by Zack Lau in QRP Power. ("Birth of A 40-Meter Transceiver," originally appeared in QEX.)

73,

Jim, KR1S