[time-nuts] 5065A phase-noise

[Magnus Danielson]

Fellow time-nuts,

As I have been measuring this, I've been surprised by the behavior
differences of my 5065A rubidiums.

One of them has a modernization so the 00105-6013 oscillator is replaced
by a 10811 oscillator with associated support-board. This retrofit is
known as 05065-6097 [1].

Now, the phase-noise plots show two main things:

For the 00105-6013 assembly, the far out noise-floor is around -154 to
-155 dBc. This fine. However, at around 1 kHz is the 1/f flicker noise
corner, providing considerable noise. I have measured both with closed
and open-loop, but the noise is the same, so this comes from the
oscillator. The loop opens just at the EFC input of the oscillator. The
transition to 1/f^3 corner comes further down, but not really bad
location, the flicker phase sticks out.

So, then for the replacement kit, the 10811 is really good, now isn't
it? Well... turns out that the wide noise is around 12-13 dB worse than
the old 00105-6013, it's only as one gets to the closed in noise that it
raises up, and it is quite respectable. I've not measured this open-loop
yet.

So, none of them is stellar in the phase-noise department.

I've noticed that the 0565-6097 has a rather crude adaptation of the
sine into the TTL input of a 7474 flip-flop setup to act as divide by 2.
You have a series inductor and capacitor into a voltage divider-chain
that sets the midpoint. I am not quite sure that this provides good
noise properties as it squares up.

I've not spotted likely reasons for problems yet in the 00105
oscillator, most transistors seems to have pretty OK emitter
degeneration which should help to keed flicker noise down.

Have a look at ponder over these things.

Cheers,
Magnus

[1]
http://www.ko4bb.com/manuals/HP_5065A_A10_quartz_oscillator_replacement_kit_1981_restored.pdf