[time-nuts] Re: Phase Noise Measurement {External}

[Jim Muehlberg]

Tobias,

Maybe you have seen Charles Wenzel's "teclib.com" site.  Lots of fun 
stuff there.  Including a design for a LNA for precisely what you want:

http://techlib.com/files/lowamp.pdf

I built this about 15 years ago.  There are probably better LN op amps 
out there now.

Take a look at this guy: (Marco Reps)

https://youtu.be/XpbDMo8an5w

He's a "voltnut", but that's OK.  We're all nuts.

Oh, and certainly, you need to read Linear application note #124 by Jim 
Williams.

Good Luck!

Jim


On 2023-02-24 4:00 AM, Pluess, Tobias via time-nuts wrote:
> Dear all,
>
> for a long time I had this project on my todo list. I recently started with
> building my own phase noise measurement equipment.
> I have a batch of brand new UCT 108663 Oscillators (new old stock
> possibly?) and had the possibility to measure them a while ago on a
> Keysight E5052B analyser. I now want to make my own PLL + LNA to measure
> the oscillators on my own spectrum analyser.
> For this, I built the circuit shown in the image. A SRA-1 mixer is used as
> phase detector. Since I want to avoid a negative voltage rail, I connected
> the IF centre tap to a reference voltage, such that the IF output signal
> swings around VCC/2 and not around ground.
> The amplifier and integrator are configured in the same way. So far, the
> PLL works very nicely. By changing the resistor R3 in the feedback path of
> the first amplifier, I can easily adjust the loop bandwidth. Oscillators
> stay nicely in quadrature. OK, so far this works.
> Now comes the interesting part. The LNA. I would like to use AD797 or
> similar (ADA4897 maybe?). I wonder whether it is, from a low noise
> viewpoint, possible to use the schematic as shown? I have decoupled VCC/2
> with several different capacitors and in theory, this configuration of the
> amplifier should work. But will it in practice yield an acceptable result?
>
> I would like to avoid a negative voltage rail if possible, because the
> tuning voltage output will need to be positive anyways, and I would like to
> avoid any switching converters.
>
> thanks for any hints,
> best
> Tobias
>
>
> [image: image.png]
>
>
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-- 

Jim Muehlberg
Senior Engineer

National Radio Astronomy Observatory
ngVLA Local Oscillator Lead

1180 Boxwood Estates Rd B-111
Charlottesville, VA 22903-4602
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C 434.422.2017