bg7tbl gpsdo master reference

[edpalmer42]

Either your probe isn't making a good connection in the socket or there's a bad connection further in.  The picture you linked to shows the result of looking at a square wave with a very small capacitor in series.  You'd see that with a bad connection such as a cracked solder joint.  You should see a square wave with limits of something like +-5V to +-10V.  Use your scope probe to trace the signal back towards the Trimble board.

Ed

[metrologist]

non-bg7tbl gpsdo discussion:

Some Trimble receivers, like the Thunderbolt, have some firmware issue where they may fail to start with the right date after yesterday.

>My GPSDO came in. It is not BG7TBL, but similar with the Trimble module...

Just guessing that one can probably compensate for it in software if its basic functionality remains unchanged.

Maybe I should not post in this thread because it is not BG7TBL module? I'm not sure what there is to compensate for at this point?

I don't know what it's doing with the LEDs or what state it's in; these are the LED's in sequence:

1. Amber LED is either solid or blinking.
2. Red LED is off, blinks fast, or blinks slow.
3. Red LED always blinks with PPS.
4. Green LED is always on when powered.

When I first powered up, the 1 amber LED blinked slow and then went solid. After a while it started blinking fast.
After longer, the 2 red LED started blinking. It did not look good so I hit the reset (button).

I don't recall the sequences, but I've had various combinations of the first two LEDs blinking fast or slow together, or with the first amber solid. According to the sellers notes:

1. ACT when working,it will flash when gps locking.
2.second one ,it will only flash ONCE when it start to working
3.1pps led.when led flash.1pps will output
> --------------
> aboved all linked from gps board that inside the box(NOT FROM THE RS232 BOARD,DIRECT CONNET TO TRIMBLE GPS BOARD)
> -----------
> 4.DC ,,,it DC working state.Apply power on it..(i made this power module fit the box and gps board)
> ------------
> mact IS BACK to factory reseting
> reset is restart.

I don't know what is actually locked, but once the amber LED was blinking fast, the red LED blinked for a few minutes, then stopped. That might mean it's locked, with a fast blinking LED seems odd though. I removed the GPS antenna and nothing changes, not in any of the states.

Edit:
Pressing MACT seems to swap amber to solid and red blinking, or amber blinking and red off.

It looks like an OCXO to me with some funny pulses out of the RS232 port. I'll ask the seller what he thinks, I'm out of thinking power.

Edit2:
Seller asks me to connect to LadyHeather. Maybe just for grins I will connect the serial line since it's 5V. Not sure if the negative 5 volts will hurt the serial-usb converter. I was also thinking that the first positive impulse could be the start of a bit and the negative pulse intended to be the end of the bit(s). Maybe some interface circuit is required?

[cdev]

Some older GPSs in GPSDOs need a GPS antenna to draw more current than most current active GPS antennas (only a very few ma) draw to not sound an alarm that the antenna is gone (when it isnt) They might want to see an older style timing antenna which likely draws a bit more current.

The GPSDOS designed for cell site use have an alarm when the GPS antenna is seen as disconnected. They likely expect a certain range of current to be drawn, a bit like a burglar alarm's bell circuit.

If the low current drain in a newer antenna was the problem, you might be able to get them to work by switching to the kind of antenna they normally use (a timing antenna) or somehow modifying the one you have so that slightly more current was drawn by whatever was plugged in as the antenna, but not too much current, which would make it think there was a short.

Have never been in this situation, and don't own a GPSDO yet either, just read about this problem recently.

[metrologist]

non-bg7tbl gpsdo discussion:

Shouldn't the serial data still come out looking like serial data? Also, what would the baud rate be for this trimble module (probably not known, but seller says MACT is back to factory, but I thought that is to force the 10M/PPS outputs?)

Is this trimble unit an upgrade to the thunderbolt or just some unknown variant? I think TheSteve had done some tests on various receivers and he listed something like a Trimble ~UCC~ that had very good PPS stability. I wondered if this is that particular module?

I'm tempted to buy a loose module of the same here to play with. I'd rather get something that actually works though. There is also the NEC modules. I'm starting to get a headache though...

Now I'm getting solid amber led with flashing red led. I think that means some kind of error. I'll look up the antenna specs he listed.

[cdev]

what kind of antenna are you using?

The UART lines for the GPS are often where the information is exchanged between GPS and other components, they may have as many as three or four bidirectional communication channels which may use different formats.. multiple UARTs, USB, SPI, i2c. Look up the manufacturers documentation.

[DaJMasta]

GPS antenna current is monitored on some units, and with the very few, there's an external IF converter and you actually see a frequency over the DC bias of the antenna connector.  Passive GPS antennas almost don't exist to my knowledge - the cable run would need to be so well shielded to let that tiny signal actually make it to the unit it's just not practical.  I've seen antennas not specify requiring any sort of power, but every one of them has had an LNA inside that requires a DC bias.


As for the Trimble unit, default baud is usually 9600 or 4800, and there's a chance it uses the TSIP standard to communicate which is not ascii characters but is raw bytes, often with slightly different communication settings (Been working with a Trimble Resolution SMT that uses normal 8 bits one stop, but uses an odd parity bit).  Often modules will also have an NMEA 0183 standard output mode, but it may not be the default.  I'd try TrimbleStudio or Lady Heather to try and talk to it if you are at least seeing activity on the output - but if it's just the waveform you showed, you're not going to get data from that.  edpalmer42's post a couple back may help with getting data out through this line - sounds like a likely board defect.

[edpalmer42]

Did you miss my reply a few messages back?

You've got a bad connection on the RS-232 output.  Find it!

As for the baud rate, you've already measured it!  I'm not sure how to read your Rigol screen, but look at the shortest time between the pulses.  That's the baud rate.  Invert it to go from sec./bit to bits/sec.  Take the closest standard bit rate.

If your Rigol is showing 20 us/div, 4 bit times is ~70 us, so 1 bit ~17.5 us.  Invert that and you get 57142 bits/sec.  So the closest standard rate is 57600 bps.  Done.

Yes, from the photo, that appears to be the UCCM GPSDO that was discussed in another message thread.  I'm not sure which thread, they're starting to breed like rabbits!   

Ed

[TheSteve]

  57600 bps is the default/proper baud rate for a UCCM receiver. Mine is still rocking along.

[cdev]

Some of my GPS receivers work well enough with a passive antenna, even indoors, to make it possible to just use one.

The signals are stronger with an active antenna.

[metrologist]

non-bg7tbl gpsdo discussion:

what kind of antenna are you using?

The UART lines for the GPS are often where the information is exchanged between GPS and other components, they may have as many as three or four bidirectional communication channels which may use different formats.. multiple UARTs, USB, SPI, i2c. Look up the manufacturers documentation.

I'm using a small 3-5V patch antenna, 28dB gain.

Did you miss my reply a few messages back?

You've got a bad connection on the RS-232 output.  Find it!

As for the baud rate, you've already measured it!  I'm not sure how to read your Rigol screen, but look at the shortest time between the pulses.  That's the baud rate.  Invert it to go from sec./bit to bits/sec.  Take the closest standard bit rate.

If your Rigol is showing 20 us/div, 4 bit times is ~70 us, so 1 bit ~17.5 us.  Invert that and you get 57142 bits/sec.  So the closest standard rate is 57600 bps.  Done.

Yes, from the photo, that appears to be the UCCM GPSDO that was discussed in another message thread.  I'm not sure which thread, they're starting to breed like rabbits!   

Ed

I did not miss the post, but was hoping the seller would notice my scope capture. How would I just connect this to LH anyway? Do the negative pulses need to be inverted, and then correct the pulse width or does that not matter (I know you said there is connection issue and can sort that out after exhausting things with seller)? Would I need to use a max232 chip to convert it to TTL? I'm using a CH340G with my Lassen LP GPS module and that works fine with LH after I use Trimble studio to set the comm to NMEA (the default TSIP does not communicate with LH, and NMEA does not communicate with Trimble studio). I think -5V pulses to my serial converter will not work.

I also have a laptop with LH with an actual serial port, but then I don't know if real RS232 to the GPSDO unit will blow up the Trimble module or something else in there, I mean it has the 1PPS pulse on that comm port.

Thanks for the help folks.

BTW, I hit the MACT button before I left it today and that made the amber LED blink. There is 4.8V on the antenna center. I can measure the current into the antenna, there are a couple more of the Chinese puck antennas on order, I think I'm using a name brand puck.

[cdev]

What does "MACT" stand for?

Did you find anything useful searching for stuff on uccm gpsdo ?

[metrologist]

non-bg7tbl gpsdo discussion:

No idea, exactly. The term appears often on Time Nuts mailer and on this forum in other threads about GPSDO's

The seller says it goes to factory default, other thread here seemed to indicate if forces output of 1pps and 10MHz, which are apparently normally off until the unit is locked. Maybe it is Manual ACT. No idea what ACT means either as that is another term/label on an LED. Maybe for active or activity?

Google gives sparse results or results that do not seem to apply.

Edit: it's also silkscreened onto the Trimble board, top of board (not my board): https://photos.google.com/share/AF1QipMrbcX7Cs9tz8OXElph4wmw7cN98hqN2SXsafAtCgdJD9KTgU1do9q7CIfz5tkJ2g?key=ZXdIYmNHaWFjVVF5eVg2eERISGtONk03eXJFR1RR

Also, how can I find this guy's post who describes the communication in detail?

https://www.febo.com/pipermail/time-nuts/2015-September/093893.html

Think I found it:
https://www.febo.com/pipermail/time-nuts/2015-August/093612.html

[cdev]

You definitely don't want it putting out a PPS or frequency reference until it can be sure its accurate.

Here is another GPSDO thread, this one is from last year.

https://www.eevblog.com/forum/projects/a-look-at-my-symmetricom-gpsdo-%28ocxo-furuno-receiver%29/650/

[texaspyro]

[

I did not miss the post, but was hoping the seller would notice my scope capture. How would I just connect this to LH anyway?

I don't know how the guy wired up the box, but on the board there is a place for a 4 pin header that has the 56k baud serial port at RS-232 levels.   This should be what is connected to the DB-9 connector (DE-9 if you want to get pedantic).  I don't have the pinouts handy, but there are posts on the forum that show what they are.

The signals you are seeing indicate a bad connection somewhere.

[edpalmer42]

Here's the signal on J5, pin 2 of my Trimble UCCM board.  ~+-5V @ 57600 bps.  This is the first two characters in the 'UCCM>' prompt - actually, it's carriage return, linefeed.  If your signal isn't somewhat similar, the fault is in the Trimble board, rather than anything on the BG7TBL interface board.  Does he process the signal at all, or just pass it to the RS-232 connector?

With GPS lock, the green led is flashing quickly.  That's the green led on the bottom of the Trimble board.  I don't know how that relates to the LEDs on the panel.

Ed

[metrologist]

non-bg7tbl gpsdo discussion:

Looks like I'll have some reading to do, but first the hard part, finding my screwdriver 

BTW, it immediately put out PPS and 10M on first power-up. I wanted to see how the signals came up.

Thanks guys!

[cdev]

Does it have a 50 connection header?

[metrologist]

non-bg7tbl gpsdo discussion:

Never mind this rest of this post. I found a different pin with the same signal as I found earlier on the RS232 port. Maybe it just needs a max232 chip to interface with it. 

I cannot tell if it ever locks. I get solid ACT with blinking on the other LED. Maybe that is locked. I'm going to go read the other thread.

=================

He has nicely made boards in there. There is a ribbon header and interface cable going to another board. The daughter board ribbon header also has an unpopulated DIP header that I probed and found good TTL signal. The trace goes to a glass diode D1 - signal good one side, spike on the other. The diode does not looked cracked, but there is something like a bubble inside, not round, just like a 3/4 filled bottle of liquid kind of line. I diode check one way .7V, the other 1.7V (I get similar readings on a scrap board with similar diodes - measured in circuit). The diode goes to pin 17 of 74ACT244.

Also, I tried all the baud rates. First decode happened at 115200 (I had polarity negative here).  Higher rates gave more characters, but nothing particular good.

[cdev]

https://www.ti.com/lit/ds/symlink/max3232.pdf 
will give you more UARTS

[metrologist]

non-bg7tbl gpsdo discussion:

I wired up a max233 this morning and it just squared off the very short impulses, I guess what one would expect, and it does not communicate of course.

It could be the ribbon cable not making good contact, but then I'm perplexed with the earlier circuit/result I posted above, why the other UART going through a diode changes a square data pulse to a very short impulse with decay when it just feeds a buffer? 

I also noticed by studying my PCB image above and his PCB image on the ebay ad that mine is missing an IC, the right side between the buffers (I think those are both buffers). That might not be needed, so I need to probus the Trimble and see if the ribbon connection is the problem (the Trimble unit looks nice and clean with clear coat of something - it should work!).

[usagi]

probably non-bg7tbl gpsdo discussions would be better in a separate thread...

[metrologist]

probably non-bg7tbl gpsdo discussions would be better in a separate thread...

My apologies, I mentioned that earlier...I'll fix what I can.

[Dwaine]

The seller of the star-4 has reworked the interface so it will work with Lady Heather.  There are screenshots of it in the auction.   I wish I had the newer unit that has that change.

You can modify the device.  There are two pins (needles) that connect the Star-4 GPS receiver RXD and TXD to his interface board (I think that some builds used pogo pins and others may have soldered the connections).  Remove the pins to break the connection to the GPS receiver and wire the pads to the GPS management interface TXD and RXD on the Star-4 connector.  His connection to the Star-4 connector has vias  for most or all of the Star-4 connections.

I managed to get the Star-4 working in Management mode.  I cut the two pins which went to the bottom board. Then wires from the Managements vias to the two pins spot.  Worked great.

Thanks for the help.

[Dwaine]

The Star-4 GPSDO also has a connection on the board for the 10mhz square wave.  It pretty crusty though.

[DaJMasta]

You have a 50 ohm input on the scope?  It could be just that the high impedance and the cable inductance is making it overshoot a bit.