[time-nuts] Unified VCXO Carrier Board

[Gerhard Hoffmann]

Am 23.10.2015 um 21:27 schrieb Charles Steinmetz:
>
> Use medium-speed transistors, bias both bases from the same low-noise 
> voltage reference such as an LM329, capacitively couple the emitters, 
> and use a higher supply voltage, for starters.  I use 
This evening, I have measured some oh so noisy zeners and was pleasantly 
surprised.
Other than one 40+ year old glass diode all of them were pretty low noise.

Since the LM329 was mentioned above, I tried it also. Another surprise.
HOW CAN THEY MAKE SUCH A NOISY SUBSURFACE ZENER???

Bias for the DUTs was a 1K wire resistor from 10 NiMH cells. The bias 
source does not
add any visible noise. The "shorted" trace shows the noise floor of the 
system. That is
about 220 pV/sqrt Hz.  FFT analyzer is an Agilent 89441A. It has strong 
1/f noise that is
barely hidden by the preamp. 0 dB = 1nV/sqrt Hz

> MPSH81/MMBTH81s and a power supply of around 20v (see attached 
> schematic) for a reasonably 
> optimized implementation.  Other transistors can be used, but I've 
> found that the H81s work better for squaring 1-10MHz sine waves than 
> anything else I've tried -- they hit the sweet spot of the 
> bandwidth/gain tradeoff and have a nice flat gain vs. current 
> characteristic.

Are there differences between Fairchild and Motorola?

regards, Gerhard

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