Author Topic: Economical option for precision frequency reference?  (Read 155335 times)

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Offline TheSteve

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Re: Economical option for precision frequency reference?
« Reply #350 on: March 01, 2016, 10:39:50 pm »
I have found my Trimble units to be very good at power on even without a GPS lock. However if you're storing them for several months unpowered I think you'd want to power them on for several hours with a solid GPS lock before using them to calibrate other equipment.
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Offline FlyingHacker

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Re: Economical option for precision frequency reference?
« Reply #351 on: March 01, 2016, 11:11:32 pm »
I have found my Trimble units to be very good at power on even without a GPS lock. However if you're storing them for several months unpowered I think you'd want to power them on for several hours with a solid GPS lock before using them to calibrate other equipment.

I assume they feed a control voltage to the OCXO PLL based on the GPS info. Do you know if that control voltage is stored between boots? Or is power on today the exact same as power on last year? (Rather than the same as the last power off?)
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Offline motocoderTopic starter

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Re: Economical option for precision frequency reference?
« Reply #352 on: March 01, 2016, 11:35:18 pm »
I have found my Trimble units to be very good at power on even without a GPS lock. However if you're storing them for several months unpowered I think you'd want to power them on for several hours with a solid GPS lock before using them to calibrate other equipment.

I assume they feed a control voltage to the OCXO PLL based on the GPS info. Do you know if that control voltage is stored between boots? Or is power on today the exact same as power on last year? (Rather than the same as the last power off?)

It's not just a matter of preserving the control voltage in non-volatile memory, it's physical changes to the crystal that happen when it sits powered off - the longer it sits that way, the worse. There's some good info on that on the thread (may be the other thread I started on this topic).  That said, I think all those issues have to do with phase noise, not the overall usefulness of the frequency standard for 99.999% of the use cases.

FWIW, I installed an OCXO in my HP 53131A, but I've since switched over to using the GPSDO. I got a splitter and use it as the external ref for my Siglent function generator as well.


 

Offline FlyingHacker

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Re: Economical option for precision frequency reference?
« Reply #353 on: March 01, 2016, 11:52:54 pm »
I assume they feed a control voltage to the OCXO PLL based on the GPS info. Do you know if that control voltage is stored between boots? Or is power on today the exact same as power on last year? (Rather than the same as the last power off?)

It's not just a matter of preserving the control voltage in non-volatile memory, it's physical changes to the crystal that happen when it sits powered off - the longer it sits that way, the worse. There's some good info on that on the thread (may be the other thread I started on this topic).  That said, I think all those issues have to do with phase noise, not the overall usefulness of the frequency standard for 99.999% of the use cases.

I see. So with the GPS whipping the OCXO into shape it can account for phase noise as well?

I have a 5 port video amp on order. I was going to convert that to 50ohm.

Do you think this eBay item is comparable to the ones you guys use:

http://www.ebay.com/itm/121530825744?_trksid=p2060353.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

EDIT: This seller looks better:
http://www.ebay.com/itm/10MHZ-Output-Sine-Wave-GPS-Disciplined-Clock-GPSDO-Antenna-Power-Supply-USA/281802105734?_trksid=p2047675.c100011.m1850&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D1%26asc%3D35851%26meid%3Dbd3ea62677a64cec9b16b74b0a4ecc33%26pid%3D100011%26rk%3D1%26rkt%3D7%26sd%3D281701995263

I see a few out there, and want to make sure I get the "good one."

Thanks!
« Last Edit: March 01, 2016, 11:56:38 pm by FlyingHacker »
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Offline motocoderTopic starter

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Re: Economical option for precision frequency reference?
« Reply #354 on: March 02, 2016, 12:10:58 am »
I see. So with the GPS whipping the OCXO into shape it can account for phase noise as well?

No, the GPS is very good for long-term stability, but bad for short-term stability. The OCXO is exactly he opposite - very good for short-term stability, but not good for long-term stability. By using the GPS signal to slowly condition the OCXO, we get the best of both worlds.

Also, FWIW, my GPSDO takes about 24 hours to pronounce itself at full quality after being off for a significant amount of time.

I have a 5 port video amp on order. I was going to convert that to 50ohm.

I think a lot of people go that route. I ended up getting the TAPR TADD-1, but only because at the time I was having trouble finding a good used dist. amp on eBay, with the exception of some giant units that were not practical for me.

Do you think this eBay item is comparable to the ones you guys use:

http://www.ebay.com/itm/121530825744?_trksid=p2060353.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

EDIT: This seller looks better:
http://www.ebay.com/itm/10MHZ-Output-Sine-Wave-GPS-Disciplined-Clock-GPSDO-Antenna-Power-Supply-USA/281802105734?_trksid=p2047675.c100011.m1850&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D1%26asc%3D35851%26meid%3Dbd3ea62677a64cec9b16b74b0a4ecc33%26pid%3D100011%26rk%3D1%26rkt%3D7%26sd%3D281701995263

I see a few out there, and want to make sure I get the "good one."

There is this guy in China who has made himself a little PCB to which contains the LEDs, a TTL to RS232 converter chip, mount points for the BNC connectors, and a linear regulator. To this board, he attaches various surplus GPSDO boards from various manufacturers, all of which were manufactured for the cell industry. He also has one GPSDO of his own design, which is the one you list. It is actually pretty decent, except that the frequency is very slightly off due to some error in his calculations. I think the RS-232 interface is also a little whacky (or maybe that unit doesn't even have one, I can't recall). Check out this thread for details on all the BG6TBL units:

https://www.eevblog.com/forum/testgear/bg7tbl-gpsdo-master-reference/

If you can find the BG7 unit with the STAR4 board inside, which is made by and uses an Oscilloquartz OCXO, that is the one IMHO to get. It's got a sensitive GPS chip, very good OCXO, and with a small mod to swap the RS232 connection inside the BG7TBL box, you can send commands and receive info to/from the internal processor.
https://www.eevblog.com/forum/testgear/bg7tbl-gpsdo-master-reference/msg722795/#msg722795
« Last Edit: March 02, 2016, 12:37:00 am by motocoder »
 

Offline FlyingHacker

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Re: Economical option for precision frequency reference?
« Reply #355 on: March 02, 2016, 12:56:25 am »
Yeah, I found the other thread. I don't seem to be able to find one of the STAR4 models. Grrr.... Anyone?
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Offline motocoderTopic starter

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Re: Economical option for precision frequency reference?
« Reply #356 on: March 02, 2016, 01:44:54 am »
Yeah, I found the other thread. I don't seem to be able to find one of the STAR4 models. Grrr.... Anyone?

AFAIK, this guy at 168electronics is hording the actual GPSDO inside the BG7TBL wrapper. He does not want to sell them in small quantities.

http://www.168electronics.com/oscilloquartz-star-4-osa-oem-10mhz-gps-clock-p-122.html
 

Offline usagi

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Re: Economical option for precision frequency reference?
« Reply #357 on: March 19, 2016, 03:37:07 pm »
some of the 2015-09-17 models are apparently being manufactured with oscilloquartz ocxo's. you should ping the seller to verify if it's a morion or oscilloquartz (if you actually care).

in any case the most important detail is you get a bg7tbl with a ublox gps receiver.

Offline dagg

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Re: Economical option for precision frequency reference?
« Reply #358 on: August 14, 2016, 02:16:43 pm »
I have been running my BG7TBL / 2014-12-09 for quite a while now and it is working fine. I have been trying to get it working as a source for an NTP server using the instructions at: http://www.satsignal.eu/ntp/NTP-on-Windows-serial-port.html

I cannot get the receiver t change its settings to match the requirements to work at 4800 baud and use only $GPRMC sentences. I am using the u-center software but none of the settings I send take hold. With the default settings the NTP server software does not use the GPS as the clock.

Any suggestions?

You don't need the (coarse gps) time of the gpsdo, only the pps time sync from it if you manage to see that signal on the windows serial port. In linux (raspberry pi 3) that is no problem.

The clue is:

server 127.127.22.0 minpoll 4 maxpoll 4
fudge 127.127.22.0 refid PPS

and get your coarse time in the normal way through an internet time server.

Jan.

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Offline Lee

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Re: Economical option for precision frequency reference?
« Reply #359 on: November 01, 2016, 05:04:54 am »
I know these units might be a few dollars more than the BG7 units but how come no one has experience with units such as :

Leo Bodnar Unit
http://www.leobodnar.com/shop/index.php?main_page=product_info&products_id=234

Nick Sayer
https://www.tindie.com/products/nsayer/gps-disciplined-xcxo/

And I recently discovered a GPSOD by Bob Stewart that looks very promising.
http://ae6rv.com/

I am very interested in the BG7 GPSDO's but I keep wondering if spending a few dollars for a unit that is a more modern design and has support might be a better investment in the long run. The BG7's seem to be a little bit of crap shoot as to what surplus gps and oscillator are available.

Anyone using any of these units ?

Lee
 

Offline TheSteve

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Re: Economical option for precision frequency reference?
« Reply #360 on: November 01, 2016, 05:16:55 am »
You can buy surplus Trimble units for less then 60 USD shipped on ebay, tough to beat the performance per dollar.
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Offline Vgkid

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Re: Economical option for precision frequency reference?
« Reply #361 on: November 01, 2016, 06:32:13 am »
From the Time nuts mailing list, the AE6RV version will be interesting.
If you own any North Hills Electronics gear, message me. L&N Fan
 

Offline Lee

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Re: Economical option for precision frequency reference?
« Reply #362 on: November 02, 2016, 02:29:16 am »
You can buy surplus Trimble units for less then 60 USD shipped on ebay, tough to beat the performance per dollar.

Yes but that is not exactly plug n play GPSDO. You are buying a pig in a poke with no idea of the condition or accuracy.
If someone is trying to get a dead-nuts frequency standard and you don't have $1000 of dollars of calibrated test gear and Rubidium standard then that $60 might sounds like a deal but in the long run is it really worth it ?

I love finding a great hamfest bargain as much as the next guy but I wonder if an aging and deaf gps is really a smart move.
This new generation of GPSDO's are small, accurate, have super sensitive receivers and offer firmware updates and human being on available to help with questions.

I guess what I am suggesting is it might be fun to experiment with a bargain gpsdo board but in the long run does it make good sense financially and in regards to accuracy?

For example: You can get a BG7 setup for around $160. From what I gather from the forum they have had a wide range of every changing surplus OCXO's.
No specs, no measurement, no idea of what you will end up with.

But for $200 someone could purchase something like a Nick Sayers GPSDO with documentation, actual measurements/specs and support.

I think what I am trying to get across is to remind people there Price and there is Cost. And the lowest price might not actually be the lowest in cost in the long run.

 

Offline TheSteve

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Re: Economical option for precision frequency reference?
« Reply #363 on: November 02, 2016, 03:27:16 am »
You have valid points, but I don't think it is that much of a crap shoot buying one unless it is physically damaged - and if it is you can get a refund or replacement. The thread title is economical - pretty tough to beat 60 bucks for a Trimble. Of course you can get better/newer but if someone needs one for the lowest cost possible the surplus Trimble wins. They weren't scrapped because of the GPSDO performance, it was because the cellular protocol in the base station they are pulled from is obsolete.

VE7FM
 

Offline rickells

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Re: HP 70K / HP 70000 MMS Microwave system Thread
« Reply #364 on: February 11, 2018, 10:14:47 pm »
hi,

Please note the start of a Thread for the HP 70000 or HP 70K MMS system & modules:
Future discussion hopes to include: Configuration, Use, repair, software, etc... to further understanding.
HP 70004a, HP 70205a & HP 206a Display units + the HP 70001 Mainframe & a host of HP 70xxx modules.
See:
        https://www.eevblog.com/forum/testgear/hp-70khp-70000-modular-measurement-system-thread/msg1420425/#msg1420425

thank you
 


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