[time-nuts] Antennas for Symettricom 2500 Time Source

[Bruce Hunter via time-nuts]

Has anyone stumbled across the 12V antennas for Symmetricom 2500 Time Source 
units.  The basic 23 dB model was a Symmetricom  112-1-02, furnished as 
part of the 093-03110-11 kit.


They also offered a 40 dB model, 112-8-02 with the 093-30110-12 kit and a 
50 dB model, 112-8-03 as part of the 093-30110-13 antenna installation kit.


I have never seen noticed any of these offered on eBay, even though the model 
2500 Time Source (with its SRS PRS-10) is now obsolete.  It appears antennas 
may have been left behind on the roofs when these installations were upgraded.



Bruce, KG6OJI
 
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[time-nuts] WWVB: measuring local 60 KHz noise

[Bruce Hunter via time-nuts]

I have found the proximity of my home computer has kept a bedroom projection 
clock from locking to WWVB.  Apparently the noise radiation from the computer 
effectively jams the 60 kHz signal.  

By setting the clock out on a deck about 30 feet further away from the 
computer, the clock locks up every time in about five minutes.  I take the 
batteries out to reboot the clock.  Otherwise it waits until after midnight to 
began searching for the WWVB signal.  Presumably the designers felt 60 kHz 
noise levels were lower at that time of night.

Bruce, KG6OJI
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[time-nuts] WWVB: measuring local 60 KHz noise

[Bruce Hunter via time-nuts]

I have found the proximity of my home computer has kept a bedroom projection 
clock from locking to WWVB.  Apparently the noise radiation from the computer 
effectively jams the 60 kHz signal.  

By setting the clock out on a deck about 30 feet further away from the 
computer, the clock locks up every time in about five minutes.  I take the 
batteries out to reboot the clock.  Otherwise it waits until after midnight to 
began searching for the WWVB signal.  Presumably the designers felt 60 kHz 
noise levels were lower at that time of night.

Bruce, KG6OJI
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[time-nuts] Phase-Matrix 598A Service Manual

[Bruce Hunter via time-nuts]

The recent discussion of frequency counter testing prompts me to ask members of 
this list if anyone owns or has access to the service manual for the 
Phase-Matrix 598A frequency counter.  I have been looking for a copy for 
several years and have asked on several other forums without success.  I have 
been told that many of these counters were sold to the USAF, each with a copy 
of the service manual, and that the service manuals might start showing up 
through surplus channels one of these days.  If you happen to come across one, 
please keep me in mind.

The operations manual is available at no charge online, but the service manual 
is very expensive in relationship to the defective counter I purchased several 
years ago.

Bruce Hunter, KG6OJI
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[time-nuts] Symmetricom TimeSource 2500

[Bruce Hunter via time-nuts]

For clarification, from reading the Symmetricom manual, the TS-2500 was 
designed as a reliable Stratum 1, 10 MHz source for communications systems.  In 
addition to GPS, the unit monitors the internal SRI PRS-10, and other 10 MHz 
frequency references that are presented to it.  It tracks and compares these 
with GPS and keeps long-term records of their behavior.  In the event the GPS 
signal is lost, the TS-2500 generates a 10 MHz output from its internal 
oscillator, using the PRS-10 and any other monitored reference inputs as 
references, after first applying weighting factors developed from experience to 
determine the appropriate frequency offsets.  In other words, the PRS-10 output 
is not utilized directly, but only as a reference.  An offset is applied, based 
upon the retained past monitoring data of the PRS-10 frequency versus GPS.

Should the unit suddenly see the GPS departing from its expected frequency, as 
compared with multiple other references, it might switch to the holdover-mode, 
after computing the required offsets from past experience.

A key point is that no provision is made to control the frequency of the 
PRS-10; it is simply monitored and the offset from GPS continually recorded.  
In other words, the PRS-10 does not influence the accuracy or noise of the 10 
MHz output unless the GPS reference is lost.  

Bruce Hunter, KG6OJI
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[time-nuts] Symmetricom TimeSource 2500

[Bruce Hunter via time-nuts]

Reading the recent discussion about GPS receivers for a Stratum 1 NTP server 
caused me to reflect on the Symmetricom TimeSource 2500 I have been using for 
years as a GPS-based frequency reference.  I only turn this on for a couple of 
days when it is likely I will need it, but am not sure if this intermittent 
operation really achieves stratum 1 performance.

A disappointment of the 2500's architecture is that it burns an SRI PRS-10 in 
the background as a backup in case of the loss of GPS.  This seems wasteful to 
me as the operating life of the PRS-10 units is not unlimited.  I suppose the 
PRS-10 could be disabled, but this would require some simulation circuitry as 
the 2500 monitors the PRS-10 and goes into a fault condition if the expected 
PRS-10 presence is absent.  Certainly others have utilized these units for such 
 use.  Has anyone performed a detailed evaluation of the 2500 units in 
intermittent service?

Bruce hunter, KG6OJI

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[time-nuts] DMTD - analog multiplier vs. diode mixer ?

[Bruce Hunter via time-nuts]

I realize this would not measure frequency or phase difference; but has anyone 
used a lock-in amplifier to compare two 10 MHz signals -- for example to adjust 
a rubidium oscillator to agree with a GPS reference?

Bruce, KG6OJI
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[time-nuts] Another Philipe Patek clock

[Bruce Hunter via time-nuts]

Didn't the BBC surplus a number of similar units, along with the slaves a few 
years ago?

Bruce, KG6OJI 
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[time-nuts] Frequency Divider

[Bruce Hunter via time-nuts]

David,

I am surprised at the lack of interest in your divider boards.  These are great 
units and a very useful addition to shop frequency standards.  I fit my board 
into a former NTSC TV distribution amplifier housing and used the DA's already 
present to distribute 1, 10, and 100 MHz.  A front panel rotary switch and BNC 
allows selection of 1 Hz to 100 kHz square-waves. Along with your board, there 
was  room internally for a 1 MHz sine-wave filter and a 10 to 100 MHz 
multiplier.  By adding a switching convertor, the former NTSC DA's power supply 
was adequate to power all internals.   I have found this to be a very useful 
device.  You obviously spent a great deal of time on the design of the 
circuitry and upon getting the board manufactured and distributed.  Please 
accept my sincere thanks.  I recommend it highly to others.

Best regards,

Bruce, KG6OJI   
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[time-nuts] PRS-1- Rubidium

[Bruce Hunter via time-nuts]

Jurg,

I did not see your picture before responding earlier.  Check the dipped 
tantalum on the right for a hole that spouted acid.  The device on pillars is a 
preliminary heating resistor for the rubidium bulb.  Be sure to measure its 
spacing from the bulb, if you are going to remove the circuit board, as this is 
critical to the warm up cycle.

Bruce, KG6OJI
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Re: [time-nuts] time-nuts Digest, Vol 127, Issue 26

[Bruce Hunter via time-nuts]

Jurg,

There is a tantalum capacitor on the lamp board.  When it fails it can corrode 
the board.  I have had this happen.  You can likely replace the tantalum 
capacitor and repair the foil connections.

An issue with the PRS-10 units is that the factory has implanted settings for 
the specific unit in its firmware.  They do not give customers access to the 
commands to alter these settings.  Swapping boards likely has programmed the 
wrong bias and operating settings into the lamp driving FET.

Bruce, KG6OJI

 

 

 

-Original Message-
From: time-nuts-request 
To: time-nuts 
Sent: Sun, Feb 22, 2015 9:05 am
Subject: time-nuts Digest, Vol 127, Issue 26


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Today's Topics:

   1. Re: OXCO insulation (Andrea Baldoni)
   2. PRS10 Rubidium (Jürg Kögel)


--

Message: 1
Date: Sun, 22 Feb 2015 10:44:24 +0100
From: Andrea Baldoni 
To: Discussion of precise time and frequency measurement

Subject: Re: [time-nuts] OXCO insulation
Message-ID: <20150222094424.ga31...@sol.ermione.com>
Content-Type: text/plain; charset=us-ascii

On Sat, Feb 21, 2015 at 06:09:42PM -0600, Dave M wrote:

> What kind of foam insulation is generally used inside an OXCO?  Do all 
> manufacturers use the same kind?  Is it available in small (hobbyist) 
> amounts?

In the only one kind I opened, Milliren DOCXO, the insulation was air.

Best regards,
Andrea Baldoni


--

Message: 2
Date: Sun, 22 Feb 2015 16:44:06 +0100
From: Jürg Kögel 
To: Discussion of precise time and frequency measurement

Subject: [time-nuts] PRS10 Rubidium
Message-ID:

Content-Type: text/plain; charset="utf-8"

Fellow time nuts. I have two SRS PRS10 Rb’s that I did purchase 10 years
ago. Both have been working for the last nine years. One did fail last year
and I finally got around to looking at it in the last two weeks. The
attached picture shows the trauma to the lamp board. I do not understand
the corrosion since it has been in a very controlled environment in my
basement.

Since the failed unit does have the 1 pps loop control I moved the
processor board to the still working unit. Did not work. Does it take more
than just moving that one board to get 1 pps loop control?

Second any ideas as to what may have happened to the lamp heater board. Any
recommendations? Plan on making a replacement board. Have a power FET MRF134

Thanks



 Juerg
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[time-nuts] Are these PRS10's worth it ?

[Bruce Hunter via time-nuts]

My experience has been similar to Vasco's.  Of three defective PRS-10s acquired 
for about $100 or less each, one had a bad MiniCircuits 400 MHz VCO module and 
was an easy fix.  Another had a rubidium bulb issue that I traced to the 
driving FET.  I managed to replace the FET, but the replacement's bias 
characteristics were somewhat different than its predecessor's, keeping the 
sensing circuits in an alarm mode.  At the factory, bias adjustments are made 
in the software; but SRI does not provide access to this feature for customers. 
 I tried removing and replacing the FET with still another, but messed-up the 
circuit board in the process.  I wish now I had tried to alter the FET bias by 
adding external series or shunt resistors. 

The third unit has an intermittent condition that causes it to be slow to lock 
at times and fine at others.  I have spent hours trying to trace this, but so 
far without success.

If you decide to take a chance on these units, I would not be inclined to offer 
more than $100 as their repair is a crap-shoot.

I suspect many of the units offered for sale on eBay have been removed from 
Symmetricom TS-2500 and TS-2700 telephone industry timing sources.  PRS-10s 
from these seem to have Customer Number 123-44101-4 on the label.  I have also 
encountered PRS-10s with the Customer Numbers 123-44101-08 and -10 on the label 
and assume these were from other Symmetricom instruments.

By the way, The TS-2500 is a GPS-referenced source; however, the unit seems to 
compare its internal crystal oscillator with GPS, the PRS-10, and other 10 MHz 
sources (that can be connected for monitoring) and keeps track of their 
behaviors with a microprocessor.  It appears the PRS-10 is not locked to GPS, 
but is simply monitored and kept in reserve as a replacement frequency and 
timing source should GPS service fail.  If the PRS-10 frequency wanders out of 
the acceptable range, the TS-2500 shows a fault signal, but does not attempt to 
adjust the PRS-10.  Apparently the PRS-10's frequency is set at the Symmetricom 
factory and the unit is on its own after that.  It is included in the TS-2500 
box as baggage to be used only if the GPS timing fails. As it is kind of 
expensive to burn an SRI PRS-10 simply as a standby, although this provision is 
understandably important to telephone companies, an unmodified TS-2500 is of 
questionable utility to hobbyists.

Bruce, KG6OJI 
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[time-nuts] Strange Carrier

[Bruce Hunter via time-nuts]

Brook's suggestion to shut off your house power is an excellent one; however, 
your neighbors could be involved, too.  A portable transistor radio tuned to 
the low end of the band where there is no station would make a good electrical 
noise detector -- assuming the mystery signal has harmonics, too...

In another life I was responsible for an AM radio station operating near the 
low end of the band where man-made electrical noise is the most severe.  When 
we received interference complaints from listeners, we always sent technicians 
out to investigate as if one person complained, many more were likely affected.

Next to commercial power circuits arcing, one of the most offensive noise 
sources was SCR dimmers of all sorts.  In one memorable case the investigator 
traced the interference to a string of holiday lights strung around the eves of 
a home and controlled by a dimmer.  The system broadcast noise for several 
blocks. 

Bruce, KG6OJI
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[time-nuts] 1903 Railroad self-Winding / Self-setting Clock

[Bruce Hunter via time-nuts]

The Western Union clocks used in broadcasting up through the middle 70's were 
designed to be corrected through one-second current pulses over a standard 60 
mA teletype loop.  The clocks were wired in series like the old series 
Christmas-tree bulbs.  

Internally, the clocks employed two 1-1/2 V dry cells to supply 3 VDC to the 
winding mechanism.  This was activated whenever the clock spring ran down and 
was independent of the setting (correcting) signal.  When winding, the clocks 
emitted a soft purr.

The setting mechanism was arranged so that the second-hand was seized and 
forced to the 00 position when the clock pulse arrived at xx:59.  It was 
released at xx:00 when the one-second pulse ended. I believe a clutch mechanism 
prevented this setting action from affecting the pendulum. 

As another writer mentioned, the clocks were ideally adjusted  to operate a 
fraction of a second slow in an hour's time; thus the second-hand was pulled 
forward a bit rather then retarded.  The lead pendulum was short and the 
mechanisms not very elegant; thus the clocks were not very accurate when 
operated without the setting signal.

I believe there was also a mechanical gate that allowed the clock to be reset 
only when the second hand was close to the 00 position.

My understanding was that master clocks were installed in Western Union offices 
in the major cities where time service was provided.  These master clocks 
actually generated the one-second pulses from xx:59 to xx:00 on each hour.  
Once a day a correcting pulse was routed across the country from the Naval 
Observatory.  This was sent over telegraph circuits that were used for other 
purposes, too.  At the appropriate time a technician had to enable the path to 
the office master clock to allow it to be corrected.  This was apparently a 
manual operation.
  
In originating network broadcast programs, timing accuracy needs to be well 
within one-second as one second typically represents about three words of the 
broadcast opening.  At one point the Western Union technicians went on strike 
forcing management personnel to take over technical operations.  Soon after we 
began noticing the clock error steadily increase.  Calling Western Union did 
not seem to help as it is possible the management personnel were not familiar 
with how to route the daily timing pulse to correct their office master clock.  
After a week or so, we were forced to construct a driver for the clocks based 
upon a crystal-controlled clock that was set from WWV.  When Western Union 
indicated they were dropping clock service, we elaborated on this to a 
precision time-code generator with provision for arming so as to introduce 
leap-seconds when needed and to change from standard to daylight time on 
schedule.

In broadcasting we used both digital and analog clocks.  The digital clocks 
were used for starting network feeds, but were not very acceptable to 
announcers reading copy or talking up to a switching point.  They strongly 
preferred the proportional indication of a clock hand as it is difficult to 
translate  digital indications into time left when trying to concentrate on 
other matters. 

Bruce, KG6OJI
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[time-nuts] locking oscillators - an increase in power and/or stability ?

[Bruce Hunter via time-nuts]

The interesting discussions on this site provoked me to try the experiment with 
two, fairly identical, Gunn K-band oscillators operating at 24.125 GHz.  
Individual power outputs were +18.5 and +19.5 dBm or 0.071W and 0.089W, 
respectively.  By adding E/H tuners between the oscillator and precision 
attenuator used to measure output power,output powers could be increased to 
0.118W and 0.148W respectively, an increase of 2.2 dB in each case, and total 
power of 0.265W.

Next the oscillators wee combined with a matched magic-T.  A a Gunn oscillator, 
followed by E/H-tuner was connected to each end port.  A termination was placed 
in the top (out of phase) port,  The in-phase side port was connected to 
another E/H-tuner, followed by an HP K-382A precision calibrated attenuator, HP 
K-486A thermistor mount, and HP 432A power meter.  Adjusting the three E/H 
tuners for maximum, a power output power of +24.25 or 0.266W was attained.  
Thus no power gain was observed by combining with the magic-T.

In summary, the sum of the Gunn oscillator powers, operated individually 
without E/H tuners was 0.160W.  Adding E/H-tuners increased their total output 
to 0.265W.  When the oscillators were combined with a magic-T and three 
E/H-tuners, total power was 0.266W, virtually the same as the sum of individual 
power outputs.

Adjustment of the E/H-tuners between oscillators and the magic-T was critical 
as the oscillators tended to drop out of oscillation near the maximum power 
adjustment settings.  It appeared the tuners were resonating the output irises 
of the oscillators so as to circumvent their isolation function and drain more 
power from the cavities. This was discussed in an earlier message from John C 
Roos, K6IQL.

Conclusion:  Gunn oscillators are necessarily very inefficient devices.  Their 
stable operation depends on an output iris to limit output power so as to 
achieve a balance that provides for stable operation.  The designer's 
intentions can be overcome by resonating the output iris so as to overcome the 
limitation and increase power and efficiency at the expense of stability.

Bruce, KG6OJI 
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[time-nuts] locking oscillators - an increase in power and/or stability ?

[Bruce Hunter via time-nuts]

This is certainly an interesting phenomenon.  A couple of possible explanations 
come to mind.

First, if the pair of Gunn sources are not really locked and are oscillating at 
two different frequencies, the resulting  voltage envelope would peak at about 
double the voltage of either oscillator.  This might cause a power detector 
(that senses only voltage) to read about a 6 dB increase over one Gunn 
oscillator alone.  The waveguide low-frequency cutoff would not eliminate the 
envelope modulation as the low-frequency component is encoded as a pair of 
sidebands close in frequency to the carrier.  Think of a signal generator 
modulated with 1 kHz square-wave for use with a tuned detector.  

A second possible explanation involves the combined internal impedance of the 
Gunn diode oscillators.  Summing two of them may alter the operating point 
along the E/I negative resistance curves, changing the combined generator 
impedance, and possibly improving device efficiency.  These devices are 
relatively inefficient anyway (about 1%), so an increase or decrease in the dc 
input power is not a good indication of what's going on in the generation of 
RF. 

Bruce, KG6OJI

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