CONT vs RCON mode on the 53230A frequency counter

This is a follow-up to my earlier notes on the 53230A noise floor.

Naively I did the initial frequency-counting tests using READ?, which is wrong both because it produces data with dead-time and because the consensus for what is meant by Allan deviation assumes pi-counting.

Driven by marketing, no doubt, the 53230A employs internal averaging (something akin to lambda-counting) both with the simple READ? command and the continuous CONT mode mentioned in the manual. Amazingly you have to use the undocumented RCON mode to get pi-counting which will produce correct Allan deviations.

Here is a plot. The opportunity for making errors (with pi- vs. lamda-counting, and gap-free data) is less in time-interval mode, and I have indicated the 12 ps RMS noise floor (1.8e-11/tau in terms of Allan deviation) with a black dashed line. In RCON mode the noise floor has the same 1/tau dependence and I get about 3e-11/tau. If however you simply use the built-in settings of the counter with READ? or CONT you get a noise floor of about 2e-12/sqrt(tau) due to the internal averaging going on behind the scenes.


For a paper that explains pi- and lambda-counting see Dawkins2007 (fulltext PDF on ReaserchGate). Enrico Rubiola also has notes on counters.

Datafiles and script for ADEV and figure:

Keysight 53230A noise floor test

We got a new 53230A counter to the lab, so I decided to run some basic tests on it.

I collected time interval data using a 1-PPS source (H-maser through a SRS DG645), and wired this with a T-connector from CH1 to CH2 with a ~1 m (10 ns delay) cable. This should show the noise floor for time interval measurements as well as CH1/CH2 timing skew when measured the other way around (i.e. from CH2 to CH1). The 10 MHz external reference (at the back) was connected to a H-maser.

The results show standard deviations of 12 ps (CH1->CH2) and 11 ps (CH2->CH1) respecively, with a channel skew of 112 ps. Compare to the single-shot spec of sqrt(2)*20 ps = 28 ps and Agilent/Keysight's marketing video on youtube.

I also collected 10 MHz frequency counter readings on CH1 (source: H-maser) with gate times of 0.1 s, 1.0 s, and 10.0 s. I collected the data with a simple program that just calls the "READ?" function repeatedly, which does result in some dead-time between measurements.

Here are the results in terms of Allan deviation. I used allantools.


The time interval noise floor looks like white phase noise with an Allan deviation of 1.8e-11/tau. This is consistent with the 12 ps RMS value found above. It is left as an exercise for the reader to show that ADEV(1s) = sqrt(3)*RMS-time-interval-noise (correct??).

The frequency counting noise floor depends on the gate time, and I get 5e-12/sqrt(tau), 2e-12/sqrt(tau), and 6e-13/sqrt(tau) for gate times of 0.1 s, 1.0 s, and 10.0 s, respectively. This looks like white frequency noise. Enrico Rubiola has notes on frequency counters that may explain the numbers.

53230A counter input channel fix

Update: after the fix the counter seems OK again. 12 ps standard deviation (61k PPS-pulses, collected over 17 hours) on a cable-delay test:


A broken CH1 input trace seems to be a common problem on the Agilent/Keysight 53230A counter. This is the second unit with the same problem we have seen.

The fix is to bypass the broken trace with a wire directly from the center of the input-BNC to the next unpopulated SMD-pad.