Hello all
I've been running the TS2100 with MTI OCXO and HEOL DESIGN N024 GPS
upgrades for a few monts now. I want to share some test results of the
upgrades and how much they actually improve the performance of TS2100.
Both ot these upgrades should be familar for the followers of this forum.
In my tests I was comparing the TS2100 PPS output against Trimble
Thunderbolt PPS output in the normal state and simulated "loss of GPS
coverage" state. This way it was possible to test the performance of the
new N024 GPS board and MTI OCXO.
Thunderbolt and TS2100 was sharing same GPS antenna. Antenna cable delay
compensation was set to 100 ns for Thunderbolt. In TS2100 the cable
delay can be also set in 100 ns steps from engineering menu with telnet.
After the N024 GPS upgrade the initial offset value is -1. Thus, in my
setup with long antenna cable with 100 ns. delay the correct offset
value for TS2100 is -2:
1 ? eng tim offset
Current offset : -2 at offset unit (100ns)
With original GPS I kept this always at zero. Because TS2100 PPS output
was quite inaccurate with default oscillator, there was no notable
difference with values 0 and -2 for example. TS2100 manual defines that
PPS accuracy with original setup is less than 2 microseconds. In my own
measurement it was just about less than 1 microsecond and changed in
every second if examined nanosecond level. So the PPS output of TS2100
was quite "noisy" as default - but good enough for NTP use only.
After upgrading MTI OCXO and new GPS board for HEOL DESIGN (N024) things
really changed. Now the TS2100 PPS output stays within +-50 ns from
Thunderbolt PPS. Here's an oscilloscope measurement result over 6 hours
test period with persist mode selected for traces:
http://www.amigazone.fi/files/ts2100/ts2100.png
Yellow trace is Thunderbolt PPS and blue trace is TS2100 PPS. And here's
the PPS error on same time period reported by Thunderbolt, logged with
Lady Heather:
http://www.amigazone.fi/files/ts2100/tb.png
MTI OCXO seems to be quite sensitive to rapid environment temperature
changes. Normally there's no problem at all, but if there's any kind of
rapid variations it may interference TS2100 PPS. For example, if TS2100
top coverplate is removed "on the fly" the PPS is not within +-50 ns
anymore, it might be even several hunders nanoseconds off soon after
removing the cover.
Then the freerun performance...
If there's a temporary loss of GPS reception - or antenna is removed
temporarily, how long does the TS2100 keep the time? This puts the
oscillator under tough test.
For the NTP use only the maximum acceptaple timing error is about one
millisecond. TS2100 manual says typical NTP accuracy is 1...10
milliseconds, so anything less than 1 millisecond should be "kind of"
acceptable here.
With original oscillator this is reached even less than 90 minutes.
After OCXO upgrade it was not reached at all in four hours test period.
Four hours was selected as maximum test time because any loss of GPS
reception or possible antenna replacement etc. should be take less than
four hours. Test was terminated if PPS error was more than 1,5
milliseconds, because the TS2100 was running as NTP server at same time.
In the freerun tests the TS2100 antenna was disconnected, while keeping
Thunderbolt connected normally. Then the PPS of the TS2100 and
Thunderbolt was compared with oscilloscope and the difference was
manually logged after 30, 60, 90, 120, 150 and 180 minutes. After
upgrades the PPS error was also measured before removing the antenna and
after 240 minutes of freerun.
Each test was repeated three times. Positive result means that TS2100
PPS was late and negative means it was early (same way as oscilloscope
gives these readings). After each test the TS2100 was kept in normal
state with antenna connected at 48 hours minimum to let it recover.
With standard oscillator and original GPS:
Freerun TEST1 TEST2 TEST3
time
30 min -157 us -20 us -78 us
60 min -513 us -109 us -202 us
90 min -1,026 ms -296 us -378 us
120 min -1,680 ms -530 us -629 us
150 min (ended) -661 us -943 us
180 min (ended) -760 us -1,310 ms
With MTI OCXO and HEOL DESIGN N024:
Freerun TEST1 TEST2 TEST3
time
0 min +25 ns +38 ns +31 ns
30 min +14 ns +332 ns -74 ns
60 min +500 ns +1,17 us +238 ns
90 min +1,58 us +2,42 us +900 ns
120 min +3,16 us +3,82 us +1,77 us
150 min +5,88 us +5,06 us +2,88 us
180 min +11,5 us +6,36 us +4,04 us
240 min +38,4 us +10,0 us +7,25 us
I hope that this information is useful and interesting for TS2100 owners
planning to do the upgrades - or already done them.
Best regards,
--
73s!
Esa
OH4KJU
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