[time-nuts] Symmetricom TimeSource 2700
lists at rtty.us
Tue May 1 18:31:42 UTC 2012
The "upstream" time source may or may not be very good. Since it's PCS at
1.9 GHz and not 900 MHz CDMA, the carriers have a lot of wiggle room. You
can go in and fiddle which signal it tracks.
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Mark Spencer
Sent: Tuesday, May 01, 2012 12:41 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Symmetricom TimeSource 2700
Sorry to resurrect an old thread, but I thought someone might find this of
I purchased a 2700 intending to harvest the PRS10. Prior to cracking open
the case I powered up the unit to ensure it was basically working so I could
return it if needed. I noticed that despite not having an antenna
connected it seemed to find and track CDMA signals and after a few hours the
10 Mhz output was in a few parts of 10E-12 of my GPSD0.
After a bit of investigation I found the following
Adding an external antenna didn't seem to make much difference to the
The 1pps output is approx. 75ms out of sync with the 1pps output from my
>From time to time the 10 Mhz output experiences phase jumps of several tens
of ns. Manipulating the unit (ie. connecting to the RS 422 port) may
induce this. Power cycling the unit seems to cure the problem and the unit
usually takes an hour or two to re lock. It's possible that the lack of a
proper ground in my instalation may be causing some of the issues as well.
This problem would be a show stopper for me in terms of using this unit to
replace my GPSDO's. I'm not sure if this issue is specfic to my unit or
I've attached some initial ADEV plots showing the typical performance of the
10 Mhz output vs three of my other references. (I wouldn't put a lot of
emphasis on the results of taus of less than 100 seconds or more than 6,000
or so..) I doubt I'm going to put much more time into this unit but it's an
interesting novelty in it's original state. The results of other units may
well differ (:
--- On Thu, 11/24/11, Charles P. Steinmetz <charles_steinmetz at lavabit.com>
> From: Charles P. Steinmetz <charles_steinmetz at lavabit.com>
> Subject: Re: [time-nuts] Symmetricom TimeSource 2700
> To: "Discussion of precise time and frequency measurement"
<time-nuts at febo.com>
> Received: Thursday, November 24, 2011, 11:17 PM
> Kevin wrote:
> > I use the Craft connector for monitoring with BTMon
> rather than the RS-232 port.
> > It appears the Craft output, while spontaneously
> emitting alarm/events, does respond
> > to queries from BTMon on the Craft input.
> Everything I reported previously involved the Craft port
> feeding a PC COM port using the RJ45-to-DB9 cable supplied
> by Symmetricom.
> > Do you happen to have a RS-422/485 interface? I don't,
> but I'm interested to see
> > if any spontaneous output occurs on the TOD port.
> I have a 422/485 card here somewhere, but I haven't used it
> (maybe even seen it) in more than 10 years.
> I poked a scope at the TOD jack. The TS2500 manual
> says that (in a TS2500) Pin 1 should be PPS (positive), Pin
> 6 should be PPS (negative), Pin 5 should be TXA output
> (positive), Pin 9 should be TXA output (negative), and Pins
> 7 and 3 should be a 20 V external supply positive and
> return, respectively.
> I found PPS positive and negative on Pins 1 and 6.
> Logic low is about 1.2 V positive with respect to case
> ground, and logic high is about 3.8 V above case ground, for
> a logic range of approximately 2.6 V. The PPS pulses
> are 500 uS wide with rise and fall times of ~20-25 nS.
> I did not see any data on the TXA outputs -- the positive
> TXA output just sits at logic low and the negative TXA
> output sits at logic high.
> There is 20 V between Pins 7 and 3. As for the
> unspecified pins -- Pin 2 sits at nominally 0 Vdc, and Pins
> 4 and 8 sit at nominally 0.168 Vdc. All three have
> around 20 mVp-p of hum and noise.
> While I was at it, I poked at the RS232 connector, as
> well. Pin 3 (TX Data) has a 16 or 17 mS burst of data
> every 5 seconds (approximately), from -10 V to +10 V with
> respect to case (henceforth, 232 low and high,
> respectively). Between bursts, it sits at 232
> low. Pins 4 and 7 (DTR and RTS, respectively) sit at
> 232 high. All other pins sit at ground.
> Best regards,
> time-nuts mailing list -- time-nuts at febo.com
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