HP5065 Aging Experiment

I've completed a long run of phase data showing the HP 5065A versus Loran-C. I took ~3 day samples from the beginning and near the end, and compared the frequency offsets.

The offset was -2.79x10^-12 at the beginning, and -2.52x10^-12 at the end, of the run. Here's the full 17 day run, showing the rollovers when the signal hit the rails of the 1us recorder range.

The difference in offset is 2.7x10^-13 over 10.4 days, or 2.6x10^-14/day. That's 7.7x10^-13/month (assuming a 30-day month). That's significantly better than the quoted spec of 1x10^-11/month. Is something wrong with this analysis?
jra on 08.30.03 @ 10:42 AM EDT [link]

More on phase jump

Following up on the earlier entries about the diurnal step change I'm seeing in my Loran-C phase plots... here are two spectrum analyzer shots showing the AM broadcast band as received by the Loran antenna.

Here is a shot taken at 2000 local time and here is one taken at 2100 local time. When these were taken (August 11/12) the phase jump occurred between these two times. There are two significant differences between the two plots: first, the two strongest signals increased in strength at sunset, with the strongest going up by about 3dB. Second, two of the local stations went away completely. So, the total power seen by the receiver doubled at night, and the absence of a few signals possibly changed the number and nature of any IMD products being generated in the receiver front end.

As noted earlier, putting a 30dB attenuator in the antenna line greatly reduced the amount of the phase shift, though the most recent phase plots still show a diurnal effect that may or may not result from this.

I suspect that the high power being presented to the Austron receiver causes it to overload, and the changes at night alter the overloading, resulting in a phase shift.

If this is the case, the right way to fix the problem is to put a low-pass filter in front of the receiver to block the AM broadcast signals while leaving the Loran signal strength alone. My next project is to build one of those.
jra on 08.21.03 @ 08:57 PM EDT [link]

5065A longer term plots

While away for a few days vacation, I kept the HP5065A via Loran-C data collection running, and just analyzed the results. I have about 3.5 days of data between phase rollovers (ie, where the 1 microsecond recorder output hits the rail and wraps to the other end.

The frequency offset is currently -3.49x10^-12 (with the C-field set at 1.82).

Here is the raw phase plot.
Here is the phase plot with offset removed. You can see that there is a diurnal effect; I haven't determined yet what is causing this.

Here is the Allen Variance.


jra on 08.20.03 @ 08:05 PM EDT [link]

Frequency adjust

I just reset the C-field on the 5065A to 1.82 -- 2 minor divisions lower than the prior setting, which should reduce the frequency by about 8x10e^-12. That should put the thing just about on frequency vs. LORSTA Dana.
jra on 08.12.03 @ 06:15 PM EDT [link]

Success???

The 30dB attenuator seems to have made the difference... it's now 30 minutes past the time where I normally see the evening phase shift, and no sign of it.
jra on 08.10.03 @ 08:57 PM EDT [link]

AM Broadcast overload?

One possible cause of the diurnal phase shift is overload from nearby AM broadcast stations. The new antenna results in some strong signals coming down the line -- about -9dBm for the strongest station. All the local stations either change power or antenna patterns (or both) at sunset, so it's possible that a change in the broadband power level seen by the Austron LORAN receiver could cause a phase shift. It's also possible that the directional antenna arrays could be a source of re-radiation, although the nearest station is about 2.5 miles away.

As a quick experiment, I inserted 30dB of attenuation in the antenna line. The Austron still locks up nicely on LORSTA Dana, though the gain figure (Status 3) is showing about 30dB higher. The noise value (Status 2) is about the same as without the attenuator -- in the 2 to 5 range. I'll log data for a day or so to see if this attenuation changes (or eliminates) the phase shift. If so, the longer term solution is to build a low pass filter that will knock down the AM stations while keeping the LORAN signals at nearly the same level.
jra on 08.10.03 @ 08:44 AM EDT [link]

New GRI, Same Story

This afternoon I switched the Loran receiver to monitoring the GRI 9960 master station at Seneca, NY. That's a bit further away from me than the Dana station, but it seems to come in with good signal strength and low noise.

It's now 0035 and, lo and behold, the same ~120ns phase shift just occurred. So, whatever is going on is local and not at the LORSTA.
jra on 08.08.03 @ 08:41 PM EDT [link]

LORAN phase jumps -- antenna related?

Just found an interesting article on some LORAN stability testing in the Netherlands where an E-field antenna showed significantly greater effects from a change in near-field signal re-radiation than did an H-field antenna -- 100ns vs 50ns. I am using a voltage-probe (E-field) antenna, so this may be a factor -- now I just need to figure out what might be changing locally to cause the change.

Check:
http://www.eu-gloria.org/2003/GNSS2003%20Loran-C%20Challenges%20GNSS.pdf for the article.
jra on 08.07.03 @ 11:12 AM EDT [link]

What's 100ns among friends?

A quick look at the current data file shows that the ~120ns daily phase shift continues -- same time and same duration each day. Next step is to see if I can copy a different LORSTA to see if the same results obtain.
jra on 08.07.03 @ 10:43 AM EDT [link]

More on LORAN phase jumps

I've captured a nice plot covering about 50 hours of the HP5065A tracking against LORAN-C (GRI 8970, Dana, IN). This plot captures two of the reciprocal phase changes noted above.

Here's the raw phase plot.
Here's the phase with offset removed.

Here is some data about those plots:

First phase increase: #23492 0027, 4 August
First phase decrease: #60192 1045, 4 August
Second phase increase: #109020 0026, 5 August
Second phase decrease: #145572 1042, 5 August

Note that for all practical purposes (there is some ambiguity because of the receiver time constant) the two phase changes are exactly 24 hours apart, and each period of increased phase lasted about 10 1/4 hours. (The times are shown in UTC; 0027 is 2027 local time (EDT).


These are the average phase values for each segment, linear offset removed:

Segment1: -48ns average
Segment2: +64ns average -- +112ns
Segment3: -58ns average -- -122ns
Segment4: +77ns average -- +135ns
Segment5: -29ns average -- -106ns

From this, I don't think this jump is the result of a 10MHz divider hiccuping; all the changes are noticeably greater than 100ns.

So, now I know what the phase shift looks like, but I still have no idea what's causing it. I'm continuing to monitor to see whether this is truly a daily event.

By the way, the 5065A C-field setting is 1.86 yielding a current frequency offset versus LORAN Dana of 4.92x10^-12.
jra on 08.06.03 @ 08:09 PM EDT [link]

HP5065A via LORAN-C

I finally got a nice run of the HP5065 via the Austron 2100F LORAN-C receiver. The plot clearly shows a pair of sudden phase jumps, one up and one down. The linear frequency offset is about 4.4x10e-12, but I'm continuing the run to get better frequency offset and drift data.

Here's the raw phase data.
And the phase data with frequency offset removed.
And the Allan Variance.
jra on 08.04.03 @ 07:31 PM EDT [link]

If you've come here to find another (?) exciting, sexy weblog full of observations both witty and meaningful, you've come to the wrong place. I don't have any reason to believe that you'd find anything in my life very interesting.

This blog has one simple purpose: to be my on-line logbook for data from my experiments in ham radio and time/frequency measurement. If you want to know when I last adjusted the frequency of my Rubidium standard, then this is the place to be. Otherwise, forget it.
jra on 08.03.03 @ 10:11 AM EDT [link]