Author Topic: Unknown GPSDO but BG7TBL logo on the circuit board and OCXO !  (Read 21143 times)

0 Members and 2 Guests are viewing this topic.

Offline Diabolo

  • Regular Contributor
  • *
  • Posts: 124
  • Country: fr
Unknown GPSDO but BG7TBL logo on the circuit board and OCXO !
« on: January 24, 2018, 04:35:20 pm »
Hello,

I bought this GPSDO 10 Mhz in aluminum box via EBay (or aliexpress) for +/- 98$ and I am very satisfied.
It can provide a square or sinusoidal wave by moving a component on the output.
Pins 14-15-16 Neo7 are open, but they can be arranged to vary the baud rate.







Regards,
Diabolo
« Last Edit: February 08, 2018, 06:57:27 pm by Diabolo »
 

Offline Kean

  • Supporter
  • ****
  • Posts: 1216
  • Country: au
  • Embedded systems & IT consultant
    • Kean Electronics
Re: New GPSDO BG7TBL
« Reply #1 on: January 24, 2018, 05:40:20 pm »
 

Offline Diabolo

  • Regular Contributor
  • *
  • Posts: 124
  • Country: fr
Re: New GPSDO BG7TBL
« Reply #2 on: January 24, 2018, 05:55:38 pm »
Hello,


I have seen and read the whole topic, but it is not the same device in its design, it is an "economic" version with a Vcxo (?) apparently and not externally signed BG7TBL on its facade.
In order not to mix the GPSDO ranges and overload the topic of the "big" GPSDO with Ocxo, I think this new GPSDO deserves its topic, in my opinion.


Regards,
Diabolo
« Last Edit: January 24, 2018, 06:00:41 pm by Diabolo »
 

Online TurboTom

  • Super Contributor
  • ***
  • Posts: 1016
  • Country: de
Re: Unknown GPSDO but BG7TBL logo on the circuit board.
« Reply #3 on: February 03, 2018, 11:40:30 pm »
I got one of these compact GPSDOs as well recently (...not that I'ld really need it...  :P) and had some "toy time" with it today.
First thing I noticed is that the GPS receiver isn't one of the most sensitive ones...while others (tablet, cell phone) work behind the window, I had to place this receiver's antenna under free sky. Well, so be it... At least, the receiver then quickly locks on the satelites. But it takes a considerable time after this for the VCO to get accurate, at least 15 to 20 minutes for the "Error" led to turn off which corresponds to an accuracy of the 10MHz output of 100mHz as the manufacturer states (actually, it's slightly better than this when the light turns off).

To take some measurements, I connected the GPSDO to the "A" input of my HP 53310A Modulation Domain Analyzer and used my Rb standard (LPRO101-based) as an external reference for the MDA.

The performance seems to be quite good, the histogram is symmetric and resembles a Gaussian distribution quite well though it appears to be a little too "peaky". But I wouldn't worry about this, I've seen much worse reference oscillators.

The short-term jitter also isn't too bad at a 6mHzpp and a standard deviation of 900µHz (though I'm not sure how much my Rb reference contributes to this). The 1mHz digit of the average wanders up and down by a count or two over longer times. When I tested my Rb standard against another, identical one, I got two more stable digits of the average, so I guess this really is an effect of the GPSDO.

Finally, I turned the GPSDO by 90° along the longitudinal axis of the enclosure during the measurement, the effect is shown in the third photo. The jump of 15mHz is considerable but the frequency slowly returns back to where it's been before. Also tapping the enclosure results in frequency excursions so the GPSDO should be carefully isolated from any vibration. Otherwise, it seems to perform quite well.

Hope some members might find this information helpful!

Cheers,
Thomas

P.S. Sorry for the crappy screenshots -- had to move the MDA upstairs from the basement in order to get clear sky access for the GPSDO antenna and I didn't want to install the GPIB equipment to take proper digital screencopies as well...

P.P.S. I found in my GPSDO the 10MHz BNC's terminals not to be soldered to the PCB at all (manual jobby -- probably someone simply forgot them). This shows that it's always a good idea to have a peek inside such "el cheapo" gadgets prior to using them.
 
The following users thanked this post: Alfons, kj7e, shakalnokturn, Hans_18T

Offline Diabolo

  • Regular Contributor
  • *
  • Posts: 124
  • Country: fr
Re: Unknown GPSDO but BG7TBL logo on the circuit board.
« Reply #4 on: February 04, 2018, 09:01:56 pm »
Hello,

Personally my GPSDO-PLL receives the satellites under the roof of the house, but near a window. It seems very sensitive and fast. I made an RS232 plug and used the "Lady Heather 5.0" software that works well with Windows 10.
The GPSDO is intended for 2 formats VCXO boxes, what is the format installed on your GPSDO?
Could you post pictures of the 2 sides of the printed circuit (board) of the device to make a comparison with mine?
The GPSDO uses (BT1) a small 3 volt LIR rechargeable battery MS621FE-FL11E for the memory of the acquired parameters which must be recharged by leaving the GPSDO long connected to the mains.
- https://fr.aliexpress.com/item/100-NOUVEAU-MS-621FE-MS621FE-Rechargeable-3-V-Batterie-de-Secours-MS621FE-FL11E/32838308583.html

Regards,
Diabolo

Edit : After verification, this new GPSDO - PLL bought $98 contains an OCXO, not a VCXO.
The metal case Ocxo becomes very hot after a few minutes of operation.
The deal is excellent !!
« Last Edit: February 08, 2018, 06:51:31 pm by Diabolo »
 
The following users thanked this post: TurboTom

Online TurboTom

  • Super Contributor
  • ***
  • Posts: 1016
  • Country: de
Re: Unknown GPSDO but BG7TBL logo on the circuit board.
« Reply #5 on: February 04, 2018, 09:39:40 pm »
Diabolo - my version of the GPSDO is exactly the same as yours, same big VCXO (with obviously a label removed that must have been stuck to the top). So it wouldn't make much sense for me to open the enclosure again and take photos. Thanks for notifying me of the battery details. I simply identified it as a Li chemistry primary cell, didn't know it's rechargeable. I'll follow your advise and leave it powered on for a while.

I didn't monitor the serial data stream but may do so later to get a better idea of the sensitivity of the GPS section.

Actually, I prefer my Rb standard as a reference source, simply because it locks in less than five minutes and after that, the drift is minimal. And it doesn't need an antenna so I can run it in any place. I got myself the GPSDO because I intended to get an idea about the absolute accuracy of my Rb source (it's also adjustable within a very small range) but when about a year ago I tested my Rb source against an identical one, jitter and offset was so small that it appears to be neglible against this GPSDO. Hence, I guess I'll leave my Rb source adjustment port untouched and keep it as "my" primary standard.

Still, for the price I guess the GPSDO is a good deal. Moreover, the power consumption is much lower than of any atomic oscillator, so it's a no-brainer to keep it running 24/365.
Edit: Sine quality is quite nice by the way.

Cheers,
Thomas
« Last Edit: February 06, 2018, 06:18:01 pm by TurboTom »
 

Offline Diabolo

  • Regular Contributor
  • *
  • Posts: 124
  • Country: fr
Re: Unknown GPSDO but BG7TBL logo on the circuit board.
« Reply #6 on: February 04, 2018, 11:41:49 pm »
@Turbotom.

Hello,
Thank you for the feedback.
Your GPSDO is identical to mine, so pictures of the board are useless of course.
I find this GPSDO very well for its price, its low consumption, and its accuracy suits me very well.
It is always interesting to have a stable and accurate reference source to calibrate or check a meter.

Regards,
Diabolo
 

Offline Diabolo

  • Regular Contributor
  • *
  • Posts: 124
  • Country: fr
Re: Unknown GPSDO but BG7TBL logo on the circuit board.
« Reply #7 on: February 08, 2018, 05:39:54 pm »
Hello,

After verification, this new GPSDO - PLL bought $98 contains an OCXO, not a VCXO.
The metal case Ocxo becomes very hot after a few minutes of operation.
The deal is excellent !!



Regards,
Diabolo
« Last Edit: February 08, 2018, 06:51:47 pm by Diabolo »
 

Online TurboTom

  • Super Contributor
  • ***
  • Posts: 1016
  • Country: de
Re: Unknown GPSDO but BG7TBL logo on the circuit board and OCXO !
« Reply #8 on: February 10, 2018, 07:09:58 am »
Wow, this is great news! I didn't operate mine while I had it apart so I didn't notice. But of course the enclosure of the VCXO appears rather big, off-the-shelf TCXOs nowadays are no more than a grain of rice (or less)...

I guess I'll have to find a more convenient position of the GPS antenna and do a long-term observation. The MDA is a very convenient instrument for checking two frequency sources against each other (one has to be 10MHz since it's got to be used as the external reference). Anyway, I guess for all amateur applications I can think of, this GPSDO is more than accurate enough. And at that price equipped with an ovenized VCO - perfect!

Cheers,
Thomas
 

Offline movie

  • Newbie
  • Posts: 1
  • Country: at
Re: Unknown GPSDO but BG7TBL logo on the circuit board and OCXO !
« Reply #9 on: February 16, 2018, 08:14:19 am »
Hello,
has anyone some information how to select the square wave output?
What are the pins on JP4 for?

Thanks and regards,
movie
 

Offline charly724

  • Newbie
  • Posts: 4
  • Country: de
Re: Unknown GPSDO but BG7TBL logo on the circuit board and OCXO !
« Reply #10 on: February 23, 2018, 07:03:02 pm »
Hello,
I've received also the little PLL-GPSDO. My version comes with BG7TBL marked outside and works very well.



Regards
Charly

« Last Edit: February 24, 2018, 10:33:33 am by charly724 »
 

Offline charly724

  • Newbie
  • Posts: 4
  • Country: de
Re: Unknown GPSDO but BG7TBL logo on the circuit board and OCXO !
« Reply #11 on: February 24, 2018, 09:34:41 am »
Hello,
some testing results :-+:
- sine wave output (50Ohm) = 1.2Vpp; 0.424 Vrms or 5.55dBm
- DC input current at 12V = 260mA reduced to 120mA after 2 minutes
- frequency accuracy is higher than my measuring accuracy
- RS232 works well with Lady Heather







Regards
Charly
« Last Edit: February 27, 2018, 10:30:30 am by charly724 »
 

Offline jpb

  • Super Contributor
  • ***
  • Posts: 1751
  • Country: gb
Re: Unknown GPSDO but BG7TBL logo on the circuit board and OCXO !
« Reply #12 on: February 24, 2018, 07:59:20 pm »
- frequency accuracy is higher than my measuring accuracy
If you use the TF930's computer interface  then you can extend the gate time to get more precision though with longer gate times the two GPSDOs will agree with each other more anyway so you might not gain a lot. The counter keeps the counts going continuously so if there is a frequency difference and the phase difference reaches 20 nanosecs then the frequency value will change at that point and you could estimate how long it took for a 20nsec shift.

 

Offline 0xdeadbeef

  • Super Contributor
  • ***
  • Posts: 1529
  • Country: de
Re: Unknown GPSDO but BG7TBL logo on the circuit board and OCXO !
« Reply #13 on: February 27, 2018, 07:13:29 pm »
Did you guys get any kind of documentation for this thing?
Like what do the different LED states/blinking codes mean exactly and if the UART output is TTL level.
Or, well, maybe even some UART protocol information?
Trying is the first step towards failure - Homer J. Simpson
 

Offline Gyro

  • Super Contributor
  • ***
  • Posts: 6576
  • Country: gb
Re: Unknown GPSDO but BG7TBL logo on the circuit board and OCXO !
« Reply #14 on: February 27, 2018, 08:50:07 pm »
They're shown in this listing https://www.ebay.co.uk/itm/PLL-GPSDO-GPS-Tame-Disciplined-Clock-Sine-Wave-GPS-Receiver-10M-1PPS-RS232/162871058138?hash=item25ebdf1eda:g:nHkAAOSw1zhaas8s

Quote
- PWR:power/GPS lock indicate,flash:GPS unlock;on:GPS lock;off:not power
- ALM:alarm led,on:frequency deviation accuary>0.1Hz,offï¼?frequency deviation accuary<=0.1Hz
- Rear panel:DC-IN:12V power inputï¼?5.5-2.1 socketï¼?inside is positive ,ouside is negative
- RS232:GPS NMEA output 9600BPS,compate RS232 signal
Chris

"Victor Meldrew, the Crimson Avenger!"
 

Offline 0xdeadbeef

  • Super Contributor
  • ***
  • Posts: 1529
  • Country: de
Re: Unknown GPSDO but BG7TBL logo on the circuit board and OCXO !
« Reply #15 on: February 27, 2018, 09:29:33 pm »
Well, yeah, that's better than nothing but hardly a proper documentation.
E.g. Diabolo said "It can provide a square or sinusoidal wave by moving a component on the output."
I would expect that stuff like this would be described in a manual. As well as things like how long it takes for the OCXO (?) to stabilize etc.
Trying is the first step towards failure - Homer J. Simpson
 

Offline ChuckDarwin

  • Contributor
  • Posts: 45
  • Country: mh
Re: Unknown GPSDO but BG7TBL logo on the circuit board and OCXO !
« Reply #16 on: March 05, 2018, 04:45:27 am »
How hot does the case get after it has warmed up: hand warmer, tea warmer, egg fryer?
-CD
 

Offline phil_lndn

  • Newbie
  • Posts: 3
  • Country: gb
Re: Unknown GPSDO but BG7TBL logo on the circuit board and OCXO !
« Reply #17 on: March 06, 2018, 04:26:22 pm »
Curious to know what the output signal does when it loses GPS signal?

I've ordered one of these to stabilise my 23cms transmitter for earth-moon-earth transmissions, it seems likely to me that during my (1 minute) transmit periods, my 23cms signal will block the GPS receiver (which operates on a similar frequency).
 

Offline 0xdeadbeef

  • Super Contributor
  • ***
  • Posts: 1529
  • Country: de
Re: Unknown GPSDO but BG7TBL logo on the circuit board and OCXO !
« Reply #18 on: March 06, 2018, 06:21:32 pm »
Mine outputs 10MHz from the start. Actually it tends to output something like 9.99999MHz when switched on and then needs quite some time to settle after the green LED stays on and the red one stays off (swings over/under 10MHz over some hours or so).

[EDIT]
Regarding the temperature: the device case stays cold (room temperature). Even the top of the oscillator enclosure is cold (room temperature). Inside the enclosure the temperature seems to be ~34°C or so. At least that's the temperature of the PCB below the enclosure after some hours. IMHO this is not really an OCXO in the classical sense. The temperature seems too low and it heats up too quickly (power consumption of the power supply drops from ~5W to ~2W very quickly). Probably this is more like a TCXO with an enclosure than a typical oven.

[EDIT2]
After the GPSDO was off for ~12h, I measured the power consumption during startup again (wall wart). I starts at around 5.1W and falls down to slightly over 2W after quite exactly 1 minute (at 23.5°C room temperature). It then slowly drops and settles at ~1.9W.
So there obviously is some kind of heater/temperature regulation but it's a bit too fast for a typical OCXO. Obviously this is related to the observation of rather low temperatures.
« Last Edit: March 07, 2018, 06:40:00 pm by 0xdeadbeef »
Trying is the first step towards failure - Homer J. Simpson
 

Offline phil_lndn

  • Newbie
  • Posts: 3
  • Country: gb
Re: Unknown GPSDO but BG7TBL logo on the circuit board and OCXO !
« Reply #19 on: March 16, 2018, 02:03:33 pm »
Mine showed up in the post today - pretty sure it's an OCXO, i opened it up after it had been running for a few hours and the oscillator can was noticeably warm.

0xdeadbeef: i did a bit of research on OCXOs and did find a handful of OCXOs advertised as having 1 minute warm-up time, so it's possible I think!

So far, I've found the GPS locks in about 1 minute, and the red 'alarm' LED goes off after about 5 minutes, indicating that it's on frequency.
« Last Edit: March 16, 2018, 02:06:25 pm by phil_lndn »
 

Offline 0xdeadbeef

  • Super Contributor
  • ***
  • Posts: 1529
  • Country: de
Re: Unknown GPSDO but BG7TBL logo on the circuit board and OCXO !
« Reply #20 on: March 16, 2018, 03:05:58 pm »
It's probably a matter of definition. A new high precision OCXO would cost more than the whole device. Besides there isn't any marking whatsoever on it. I'm too lazy to open it again, but as far as I recall, my impression was that the metal casing was open on the lower side.
So my guess is that they put some half decent XO or TCXO with some heater element (resistors or power transistor), temperature sensor and opamp under a metal hood to get a somewhat stable temperature.
Then again, while you could call that an OCXO, it's not what is usually meant by an OCXO.
Trying is the first step towards failure - Homer J. Simpson
 

Offline phil_lndn

  • Newbie
  • Posts: 3
  • Country: gb
Re: Unknown GPSDO but BG7TBL logo on the circuit board and OCXO !
« Reply #21 on: March 16, 2018, 05:06:42 pm »
Just found a bit of a problem with these - the 10MHz output signal is very dirty.

Listening to it on my HF radio receiver, it sounds like it's modulated with a bunch of low frequency clock signals - I notice the unit has a switching power supply built on to the PCB so it could be noise from that i guess  :-\

This probably does not matter for some applications but I'm pretty sure it writes the unit off for use as a stable reference in radio equipment (which is what I was going to use it for).

Dang.  :-\
 
The following users thanked this post: cdev

Offline Diabolo

  • Regular Contributor
  • *
  • Posts: 124
  • Country: fr
« Last Edit: March 19, 2018, 02:20:57 pm by Diabolo »
 

Offline 0xdeadbeef

  • Super Contributor
  • ***
  • Posts: 1529
  • Country: de
Re: Unknown GPSDO but BG7TBL logo on the circuit board and OCXO !
« Reply #23 on: March 19, 2018, 11:37:12 pm »
I guess we can agree that there's no new high precision 150€ OCXO in a 90€ GPSDO. Even in the more expensive larger versions with FPGA, the guys in China who create/assemble these things use old OCXOs or even boards salvaged from GSM equipment and the like. But actually they never remove the markings from the OCXOs and they advertise the OCXO with weird terms like "above than OCXO 2 order of magnitude" which I never saw for one one these cheaper/smaller devices.
So I dunno. Maybe these are salvaged lower spec OCXOs or something created in some Chinese backyard. I guess someone would have to take one of these oscillators apart and analyze its construction to be sure what it really is.
Trying is the first step towards failure - Homer J. Simpson
 

Offline texaspyro

  • Super Contributor
  • ***
  • Posts: 1404
Re: Unknown GPSDO but BG7TBL logo on the circuit board and OCXO !
« Reply #24 on: March 20, 2018, 01:12:19 am »
I've seen OCXO's in TO5 packages... if you want to know what they cost, you can't afford them.
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf