Serial outputs can usually drive several serial inputs if the cables are
short (to avoid reflections).  You can wire it yourself, serial out from
the TB to both LH and NTP, serial in from LH only.

David

On 2/26/14 11:51 AM, David J Taylor wrote:

It's not going to work.

If the purpose of running the Thunderbolt is only to drive NTP then
you don't need LH.  NTP's only tags the pulses to the nearest
microsecond, nano sec on accuracy is lost on NTP.    I'd even say the
TB is the wrong GPS for NTP.  It costs to much and uses to much power.

But if you are also, or mainly, using the Thunderbolt for it's 10Mhz
and NTP is a secondary function then a TB makes sense.

Yes you NEED the PPS on the serial cable.  Thunderbolts do not send
NMEA.  Thunderbolts send their own data format that is unique to
Trimble.  Don't modify the GPS receiver.  Make a special cable
adapter.  When you do this pay attention to polarity of the PPS
signal.  It is easy to get it backwards.  You want the raising edge of
the TB pulse to interrupt the computer.  It you invert the signal the
wrong number of times the time will be "off" by the ouse length and I
don't know if the pulse length is controlled to the level the leading
edge is.    Remember RS232 uses negative and positive voltage, data
lines use negative logic, control lines positive.  The TB's PPS is
TTL level.  Many rs232 ports do accept t/l level if you get the
polariy correct.

Again don't even bother to run an NTP server without PPS.  You may as
well just get time from some internet time servers.

You can NOT control a GPS from two ports.  Both NTP and LH will try to
send commands to the GPS.

Likely, almost certainly you need to build a small circuit board the
has two connectors that face the TB (PPS and serial) and one that
faces the computer.  The little perfboard makes a neat way to or
connect cables but you could solder up a y--cable

The best thing to do is get a cheaper GPS, and one that uses less
power to drive the NTP server.  The old Motorola Oncore series are
cheap and the new breed of very small GPSes are good too.  DOn't spend
more than $40 or $50 on a GPS to drive NTP as ,again NTP record
microseconds.

You could free up that Windows PC too.  It is not the best platform
for NTP.  Asmall ARM based system (even the Rasbery Pi) will
outperform a Windows based NTP server.  and use a LOT less power
(Power cost for a NTP server is more than you think, it came to about
$300 a year for me if I used a standard PC and a thunderbolt.
Switching to a very tiny ARM based system and a smaller GPS gave as
good performance and power savings paid for the hardware in 1/2 a
year.  $.21/KWH about 170W and 8760 hours per year comes to a $300
power bill.  My current system is powered by a 1000 mw plug-in power
cube and does not need a cooling fan.

On Wed, Feb 26, 2014 at 7:53 AM, David C. Partridge
david.partridge@perdrix.co.uk wrote:

--

Chris Albertson
Redondo Beach, California

I have some problems with My 8505A
Analyzer, it has no RF output, I checked the YTO and other frequency dividers
and it appears to be OK some times there is RF output only it will not tune and
it seems to cut out as I tune trough the frequency range.
Thank You
Sal C. Cornacchia Electronic RF Engineer
Ret.

On Wednesday, February 26, 2014 12:33:17 PM, Chris Albertson albertson.chris@gmail.com wrote:

It's not going to work.

If the purpose of running the Thunderbolt is only to drive NTP then
you don't need LH.  NTP's only tags the pulses to the nearest
microsecond, nano sec on accuracy is lost on NTP.     I'd even say the
TB is the wrong GPS for NTP.  It costs to much and uses to much power.

But if you are also, or mainly, using the Thunderbolt for it's 10Mhz
and NTP is a secondary function then a TB makes sense.

Yes you NEED the PPS on the serial cable.   Thunderbolts do not send
NMEA.  Thunderbolts send their own data format that is unique to
Trimble.  Don't modify the GPS receiver.  Make a special cable
adapter.   When you do this pay attention to polarity of the PPS
signal.  It is easy to get it backwards.  You want the raising edge of
the TB pulse to interrupt the computer.  It you invert the signal the
wrong number of times the time will be "off" by the ouse length and I
don't know if the pulse length is controlled to the level the leading
edge is.    Remember RS232 uses negative and positive voltage, data
lines use negative logic, control lines positive.   The TB's PPS is
TTL level.   Many rs232 ports do accept t/l level if you get the
polariy correct.

Again don't even bother to run an NTP server without PPS.  You may as
well just get time from some internet time servers.

You can NOT control a GPS from two ports.  Both NTP and LH will try to
send commands to the GPS.

Likely, almost certainly you need to build a small circuit board the
has two connectors that face the TB (PPS and serial) and one that
faces the computer.  The little perfboard makes a neat way to or
connect cables but you could solder up a y--cable

The best thing to do is get a cheaper GPS, and one that uses less
power to drive the NTP server.  The old Motorola Oncore series are
cheap and the new breed of very small GPSes are good too.  DOn't spend
more than $40 or $50 on a GPS to drive NTP as ,again NTP record
microseconds.

You could free up that Windows PC too.  It is not the best platform
for NTP.  Asmall ARM based system (even the Rasbery Pi) will
outperform a Windows based NTP server.  and use a LOT less power
(Power cost for a NTP server is more than you think, it came to about
$300 a year for me if I used a standard PC and a thunderbolt.
Switching to a very tiny ARM based system and a smaller GPS gave as
good performance and power savings paid for the hardware in 1/2 a
year.  $.21/KWH about 170W and 8760 hours per year comes to a $300
power bill.  My current system is powered by a 1000 mw plug-in power
cube and does not need a cooling fan.

On Wed, Feb 26, 2014 at 7:53 AM, David C. Partridge
david.partridge@perdrix.co.uk wrote:

--

Chris Albertson
Redondo Beach, California

time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

Here is interesting topic about NTP on Raspberry PI (typical usage of
ARM and Linux bread on top of it)

http://www.synclab.org/?tag=testing

Basically, TCP stack on ARM usually come from one source - its a Adam
Dunken TCP stack. Then its is MII part and the  hardware which doing
Ethernet. In my opinion, MCU (ARM) could provide excellent Ethernet
functions. However its far from serious dedicated ethernet controllers
we could see in enterprise servers.

Regards,

V.P.

On 2014-02-26 12:32, Chris Albertson wrote:

--
WBW,

V.P.

Ummm think you sent the question to the wrong group perhaps?

On Wed, Feb 26, 2014 at 12:50 PM, corcsal@yahoo.ca wrote:

On Wed, Feb 26, 2014 at 12:32 PM, Chris Albertson <albertson.chris@gmail.com

Actually the Palisades driver doesn't send commands to the Thunderbolt.  It
sends a single invalid command requesting auto messages and then parses the
data stream.  As long as primary timing packets are received it works.  A
Thunderbolt will wake up doing the right thing and if not I believe LH will
correctly initialize it.

The deeper point is correct and the Trimble devices I have experience with
have ~100ms of jitter.

Props to Jackson Labs -- my Fury has O(10) microseconds of jitter using
NMEA messages.  If only they were $100.

On Wed, Feb 26, 2014 at 9:53 AM, d0ct0r time@patoka.org wrote:

The article addresses using the Pi as an NTP server with stratum > 0.
In other words as an NTP server that uses another NTP server as its
reference clock so it uses Ethernet for time transfer.  In the OP's
case he wants to build a Stratum = 0 server that uses GPS as a
reference clock.  Ethernet "noise" will not be an issue.

The Pi might or might not be the best choise.  There are now so many
small and cheap ARM systems.  You can even re-purpose an old ARM based
router or small NAS. box.

Except as an exercise there is almost no point any more using GPS to
drive a local NTP server if you have a very good Internet connection.
My fiber Internet connection is as good as Ethernet as the Pool
Servers work well for me.  Those using slower or a widely shared
connection might not get as good a result.

--

Chris Albertson
Redondo Beach, California