Re: [time-nuts] Symmetricom 58536A

[Frank O'Donnell]

Thanks much, Kevin, interesting point. If I connect the Tbolt to the 
PD5120's DC Block port, and another GPSDO to the DC Pass port, Heather 
shows the Tbolt's status with "Tracking satellites" in green. However, 
"Antenna open" continues to display in yellow.


But it seems there was a more mundane explanation here. While moving 
cables around, I noticed that Heather's status display changed when I 
repositioned the cable between the splitter and the Tbolt. After 
replacing it with a fresh cable, the Tbolt is now working fine with the 
58536A.


If I can throw out another question, I'm not entirely clear on how the 
58536A handles bias voltages from multiple receivers. There is a label 
with "DC Power" and an arrow next to each of its four receiver ports. 
The Symmetricom information note on the unit that I was able to find 
doesn't say anything at all about bias voltages. I've heard two 
conflicting statements from other users. One said the 58536A defaults to 
using only port 1 for bias voltage (unlikely to me, given the labels). 
Another said the 58536A combines any voltages present on any of the 
receiver ports and passes them on to the antenna, but blocks any from 
going back to any of the receivers (sounds more likely). Does anyone 
believe they have the last word on this?


Thanks again,

Frank


On 8/17/20 4:22 PM, Kevin Rowett wrote:

Does the setup with the PD5120 work if the TBolt is connected to either port?

Some GPS receivers look to see if the antenna is drawing current, to determine 
if it’s alive.  With a splitter, the receiver might not see an antenna current.

I seem to recall the TBolt had a setting for that.

KR



On Aug 17, 2020, at 3:04 PM, Frank O'Donnell  wrote:

Based on a recommendation here sometime back, I bought a Symmetricom 58536A 
distribution amplifier so that up to four GPSDOs can share my rooftop Lucent 
26db twist antenna.

When I connect the antenna to its port on the 58536A, and a Trimble Thunderbolt 
to port 1, Heather shows no antenna connection on the Thunderbolt. By contrast, 
when I use the antenna and Thunderbolt (and/or another GPSDO) with a 2-port 
Instock PD5120 splitter/combiner, all devices function normally.

The 58536A information note says it needs +4.5 to 13vdc. The antenna requires 
3.3 to 5vdc. A multimeter measures +4.951vdc on the Thunderbolt's antenna port.

If anyone has suggestions, I'll be very grateful.

Frank




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[time-nuts] Symmetricom 58536A

[Frank O'Donnell]

Based on a recommendation here sometime back, I bought a Symmetricom 
58536A distribution amplifier so that up to four GPSDOs can share my 
rooftop Lucent 26db twist antenna.


When I connect the antenna to its port on the 58536A, and a Trimble 
Thunderbolt to port 1, Heather shows no antenna connection on the 
Thunderbolt. By contrast, when I use the antenna and Thunderbolt (and/or 
another GPSDO) with a 2-port Instock PD5120 splitter/combiner, all 
devices function normally.


The 58536A information note says it needs +4.5 to 13vdc. The antenna 
requires 3.3 to 5vdc. A multimeter measures +4.951vdc on the 
Thunderbolt's antenna port.


If anyone has suggestions, I'll be very grateful.

Frank


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Re: [time-nuts] TAPR TICC and TADD-2 Minis

[Frank O'Donnell]

On 5/31/20 8:14 PM, Charles Steinmetz wrote:
Doing as you are now -- feeding the T2-Mini output through coax to the 
input of your scope -- you will either need to switch the scope input 
impedance from 1 Mohm to 50 ohms (if the scope has that feature -- 
sadly, many digiscopes do not), or use a 50 ohm feedthrough terminator 
on the scope input.


Thanks for the comments. Attached is a screen shot with the 
Thunderbolt's 10 MHz output again going through the T2-Mini to the 
scope, but with a 50-ohm feed-through terminator placed on the scope's 
input.


Frank

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[time-nuts] TAPR TICC and TADD-2 Minis

[Frank O'Donnell]

Hi all, recently I bought a TAPR TICC as a learning project, and also 
bought two TADD-2 Minis to serve as sine-to-square converters for the 
two inputs. Since the TADD-2 Minis will be dedicated for this purpose, I 
simplified their assembly by just installing a jumper from pin 2 to 3 of 
the IC socket position, installed the BNC input and output connectors, 
and +12vdc power wiring. (I.e. I omitted the PIC chip, its socket and 
the other headers.)


As a test, I sent the 10 MHz out from my Trimble Thunderbolt through one 
TADD-2 Mini and to a Siglent digital scope. A screen shot from the scope 
is attached.


I have two questions at this point:

1) Does this look like a decent waveform for TICC purposes? I verified 
in advance with the scope that the Thunderbolt is putting out a clean 
sine wave.


2) For this test, I just used 50-ohm coax between the Thunderbolt and 
the TADD-2 Mini, and between the latter and the scope. I see the TADD-2 
Mini instructions suggest avoiding a 50-ohm load, instead terminating 
into a TTL or high-impedance load. Is there a recommendation for the 
best cabling to use to connect the TADD-2 Minis to the TICC?


Thanks for any advice,

Frank

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Re: [time-nuts] GPS antenna splitter recommendation?

[Frank O'Donnell]

On 4/29/20 6:01 PM, Bob kb8tq wrote:

Here’s a few:


Bob, thanks very much for the suggestions.

Five of the seven splitters in your list appear to offer a total of two 
output ports. What I'm looking for is one that will accommodate 
(specifically) three or four ports.


Of the remaining two on the list, this one:


https://www.ebay.com/itm/Mini-Circuits-ZN4PD1-63W-S-RF-Power-Splitter-250-6000MHz-Qty-Available-GOOD/133387795141?hash=item1f0e883ac5:g:tdoAAOSwAbxel2o~
 



has five outputs and costs $50. Probably usable, though I was wondering 
if going with additional output ports could increase possible loss? And 
also, the price isn't a show-stopper but is a little high for what I was 
hoping for.


The other one:


https://www.ebay.com/itm/New-Mini-Circuits-ZB6PD-2-S-800-2000-MHz-Power-Splitter/114155096838?hash=item1a942c8b06:g:jNIAAOSwedNedT92
 



isn't entirely clear to me. The text says it's a three-port, but I count 
four visible connectors that look like output ports, and two more that 
might be hiding under caps. This one goes for $19.90.


Given all of that, do either of these two seem like the optimal way to 
go if I want to plug in three or four GPSDO's?


Thanks again,

Frank


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[time-nuts] GPS antenna splitter recommendation?

[Frank O'Donnell]

I'm looking for a splitter to allow three or four GPSDO's to share my 
roof-mounted Lucent PCTEL KS24019L112C 26db GPS twist antenna.


I understand from scanning past threads that inexpensive splitters by 
companies like Mini-Circuits often turn up on eBay, but I'm having 
trouble narrowing down to one that will work for my situation. Can 
anyone recommend a specific splitter that wouldn't be too expensive?


Thanks much,

Frank




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Re: [time-nuts] Connector options for HP10811A?...

[Frank O'Donnell]

Thanks for all of the replies to my question about a connector for the 
HP10811A. Sounds like a number of good options.


Frank


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[time-nuts] Connector options for HP10811A?

[Frank O'Donnell]

I recently bought an HP10811A oscillator on eBay, only belatedly 
realizing that it's designed to interface to a 15-contact connector that 
the manual identifies as a CINCH 250-15-30-210 or equivalent.


A search turns up a vendor in Massachusetts called BMI Surplus Inc., 
that appears to have these in stock in new condition at a minimal price. 
The only hitch is that BMI's website says they're closed down due to 
COVID-19 and will not process any orders until their state government 
authorizes businesses to return. (And at this point, it's anyone's guess 
when that will be.)


To get going with the oscillator, it occurs to me that I could rig up a 
few small alligator clips and use them on the required contacts for the 
time being. Any other thoughts or suggestions on how to work this? By 
any chance are there other known sources for the right size of connector 
that might be operating right now?


Thanks much,

Frank O'Donnell
South Pasadena, California





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Re: [time-nuts] Accuracy results with Trimble Thunderbolt?

[Frank O'Donnell]

Tom,

Thanks very much, that's a great list and will keep me busy for some time.

At the hobbyist level, are there time interval counters or frequency 
counters that are particularly popular, and/or that pair well with the 
listed software?


Frank



On 3/25/20 2:30 PM, Tom Van Baak wrote:

Frank,

The software that most of us use to create Allan deviation plots is 
free and not that hard to use.
You will need ascii numerical phase or frequency data, e.g., from a 
time interval or frequency counter.



1) Stable32, by Bill Riley

See: 
https://ieee-uffc.org/frequency-control/frequency-control-software/stable32/


Documentation and a goldmine of T information: http://www.wriley.com/


2) TimeLab, by John Miles

http://www.ke5fx.com/timelab/readme.htm

Documentation and tutorials: 
http://www.miles.io/PhaseStation_53100A_user_manual.pdf



3) Allan deviation for Python, by Anders Wallin

https://pypi.org/project/AllanTools/


4) Command line tools for ADEV

adev_lib.c, adev4.c, adev5.c in my http://leapsecond.com/tools/ 
directory.



5) Excel, gnuplot, etc.

Any software that generates log-log plots can be used to make ADEV 
plots. You first calculate the statistics using CLI tools and then use 
the GUI to make the plots. This gives maximum flexibility in plotting 
clarity and style but requires more work than canned packages like 
Stable32 or TimeLab.


Normally I recommend TimeLab to new users, but I'm run into VBA and 
Excel wizards who are proficient in that environment.



6) Plotter, by Ulrich Bangert

Still used by some time nuts, maybe "not recommended for new design", 
since Ulrich is no longer with us.



/tvb



On 3/25/2020 1:44 PM, Frank wrote:
Big thanks to Attila, Frank, and Taka for your responses to my 
questions on my Trimble Thunderbolt.


I'm inclined to follow Taka's advice and reset the antenna elevation 
mask angle with LH's FE command to something between 10 and 20 
degrees. I'm guessing that this is entered in degrees (i.e. "15"), 
but I can't find anything in the LH documentation to verify this, so 
if it's wrong I'm happy to be corrected. Also, as noted I set the 
satellite signal level mask to 1 with LH's FL command, but short of 
doing a full reset of the Thunderbolt I'm having trouble figuring out 
what the default value is for this.


I appreciate Attila's and Frank's suggestions on topics to study such 
as Allan deviation to dip more toes into metrology. I've started in 
on this, though I imagine it will take a while to work through. For 
now, I wanted to throw out one follow-up question. I see that ADEV 
diagrams plotting Allan deviation against time seem to be a primary 
tool for evaluating GPSDO performance. If I wanted to compare the 
Thunderbolt to another GPSDO (for example, I also have a Bodnar 
unit), is there software not wildly beyond a hobbyist budget that 
would allow me to compile and display similar data?


Thanks again,

Frank




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[time-nuts] Accuracy results with Trimble Thunderbolt?

[Frank O'Donnell]

I hope you all don't mind a novice-level question, but I'd be interested 
in any feedback on what I'm seeing with the accuracy of the 10 MHz 
signal out on my Trimble Thunderbolt.


I bought the Thunderbolt last year used on eBay, and it appears to be of 
about 2001 vintage. Most recently it's been running continuously for 
about 2 1/2 months, attached to a roof-mounted Lucent PCTEL 26db twist 
antenna with a clear view of the sky, with the receiver located in a 
room with a relatively stable temperature. Lady Heather and Thunderbolt 
Monitor both appear to report it to be well settled-in. My main use of 
the Thunderbolt is to supply a 10 MHz reference signal to an HP3586B and 
HP3336B for frequency measurement purposes.


At the beginning of this month I remember typically seeing about 20 ppt 
accuracy for the 10 MHz reference as reported in Heather. I then used 
Heather commands to initiate an autoset of oscillator parameters (set 
antenna elevation mask angle to 0 with FE keyboard command and set 
signal level mask to 1 with FL command in order to allow collection of 
signal level data across full sky; clear signal level history with CM 
keyboard command; let run at least 6-12 hours to build up new satellite 
signal level map; issue “” autotune command, allow time to complete). 
Now I seem to be seeing about 60 ppt accuracy on average.


For my purposes, these differences are probably academic -- if I'm doing 
my math right, 60 ppt in a 10 MHz signal is 0.0006 Hz, far down in the 
noise of frequency variation due to Doppler etc. Still, I guess I've 
drunk enough of the Koolaid to wonder about the accuracy level and any 
ways to improve it.


So, some questions. Is it possible that the increase in the error seen 
could be due to the oscillator parameter autoset sequence that I ran? If 
so, is there a way to remedy this? What would be typical accuracy for 
the 10 MHz reference on a Thunderbolt? Is there anything else I can do 
with the Thunderbolt itself to increase the accuracy?


If I want to consider an alternative to the Thunderbolt that might offer 
better accuracy, is there a logical next step?


Thanks for any suggestions,

Frank


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Re: [time-nuts] Recommendations for time beginner?

[Frank O'Donnell]

ight frequency.  How much
and how often you need to do this will depend on the oscillator.   A
surplus OCXO can be had for well under $100.   A good quality pre-aged
surplus one is likely better than a new out of the box one (even of the
same time).   Other members of the list have much more experience with
which are the best, but I personally have found that the oscilloquartz ones
are typically acceptable for my needs.

A rubidium oscillator is like an OCXO on steroids.   But if you think of it
as a very very very low drift OCXO then you've probably got the right
idea.  For comparison a good OCXO will drift in a day about the same as a
rubidium will drift in a year.   You can often get a Stanford PRS10 in good
condition for around $250 or so.  The challenge is that any atomic clock
has a certain limited life due to the physics package "wearing out" in some
form or another, so it's a bit higher risk than just buying a good quality
OCXO.

Before I get to the GPSDO's let me mention about the relative ease of
trimming the above two types of references.  If you have a two channel
oscilloscope, it is rather easy to trim these.  You plug the reference
clock into one channel, set the scope to trigger off of that channel (so
the waveform is stable).   Then you plug the clock you are trimming into
the second channel.  You then adjust or 'trim' the oscillator until the
waveforms do not move (or beat) in relation to each other.

If you don't have a two channel oscilloscope, there are other ways to do
this as well.

Now back to the GPSDO's.

The thunderbolt you have is a OCXO 'disciplined' by the GPS's 1PPS output.
  It's the same as trimming the OCXO on a continual basis such that the OCXO
output always has 10 million cycles per 1 second.   There are other GPSDO's
that use other types of oscillators as well (rubidium, vcxo, etc). The
method of trimming the oscillator varies from GPSDO to GPSDO, but the
effect is typically the same: that is to adjust the 10Mhz output to
something close to 10Mhz.

As I mentioned I have a trimble thunderbolt and a BG7TBL GPSDO.   The
BG7TBL GPSDO is a GPSDO designed by a Chinese ham, and each edition seems
to be a little different, typically using a u-blox GPS receiver and
seemingly whatever surplus OCXO they can get their hands on.   Mine happens
to have a russian OCXO in it.  The quality of these seem to be rather good,
although there is a bug which affects mine and other earlier ones which
cause the long-term frequency to be very slightly off.  The very slightly
off means it runs at ~9.9 Mhz instead of 10Mhz.I beleive that

There are other designs out there as well from other vendors.   A search on
a certain popular auction site for "GPSDO" reveals a lot of options.   I've
had discussions with a couple of people who have compared several of these
and apparently the consensus is that they're typically all decent for
general use, and some are better than others, but none that they've tried
are especially bad.  Certainly they should be good enough for a reference
clock for most people.   If I didn't have a collection of oscillators
already I'd probably pick up 1-2 of these of varying types.   Maybe a
thunderbolt and one of these.

One final caveat, which may or may not be applicable to you:   In some
applications, certain types of noise can be a problem.   Depending on how
you're using the clock you may actually find that a disciplined oscillator
is not the right solution.   Generally I'm timestamping events and I'm more
interested in stability instead of precision.  So, even if the frequency of
my clock source is off by 1-2% it isn't a big deal, as long as it stays off
by exactly the same amount (within some level of precision of course).
  But if my clock frequency is always changing, then I'm introducing noise
into my measurements that I can't adjust out.   Depending on the quality of
the disciplining method, the very act of disciplining a clock can introduce
more noise than if you just let it freerun.

Hope my rambling helps.

On Mon, Jul 8, 2019 at 2:12 PM Frank O'Donnell  wrote:


Hi, I'm extremely new to the topics covered on this list, but am finding
reading the message traffic to be highly educational. I have some
questions that I'd like to put out, and apologize in advance for them
being at a greatly simpler level than most of the discussion here.

I came to time-nuts by way of an interest in frequency measurement as a
radio ham. To supply a 10 MHz signal to my gear I bought a used Trimble
Thunderbolt. I always like to have a backup, so am thinking of obtaining
another device (either a GPSDO or something else that can provide a 10
MHz signal). For a beginner, is there something else that offers
accuracy/precision at least as good as a Thunderbolt and doesn't cost
more than a few hundred dollars at most that you might recommend?

I also have some questions about using the Trimble, but will put those
in a sep

[time-nuts] Recommendations for time beginner?

[Frank O'Donnell]

Hi, I'm extremely new to the topics covered on this list, but am finding 
reading the message traffic to be highly educational. I have some 
questions that I'd like to put out, and apologize in advance for them 
being at a greatly simpler level than most of the discussion here.


I came to time-nuts by way of an interest in frequency measurement as a 
radio ham. To supply a 10 MHz signal to my gear I bought a used Trimble 
Thunderbolt. I always like to have a backup, so am thinking of obtaining 
another device (either a GPSDO or something else that can provide a 10 
MHz signal). For a beginner, is there something else that offers 
accuracy/precision at least as good as a Thunderbolt and doesn't cost 
more than a few hundred dollars at most that you might recommend?


I also have some questions about using the Trimble, but will put those 
in a separate message.


Thanks,

Frank O'Donnell



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