[HomeBrew] 2N2222A-2N3904 question

[Philip B Atchley]

Hi Jim,
Thank you for the information.  Guess I'll go with the 2N2222A 8^).

This device is to be used as the first active stage following a passive
mixer in a receiver designed for LF (0-530KC) using an IF strip of 20 Hz
wide .  While it's true that at LF atmospherics usually are the limiting
factor, it's been shown that use of a very "quiet" receiver helps a great
deal in copying right down into the noise floor.  But I have to agree, a
NF of 4 isn't bad at that frequency, I really have no data sheets other
than the NTE manual, and for all I knew they might have been much noisier
(I think of the 2N2222A as a "switch").  With only 5 hrs/month of free
web time I can't spend a lot of time "googling".

73 de Phil  KO6BB
   
On Fri, 23 Jul 2004 13:39:51 +0000 jkearman at att.net (jkearman at att.net
[Jim, KR1S]) writes:
> 
> > 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
> 
> 


73 from the "Beaconeers Lair".
Phil, KO6BB

Where DX begins at the noise floor!
Merced, Central California, 37.3N  120.48W  CM97sh

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