GPSDO Tutorial?

Buck
Posts: 37
Joined: Sun Apr 09, 2017 3:57 pm

GPSDO Tutorial?

Postby Buck » Wed Jul 12, 2017 4:23 am

I have a rev. 24 200D, thinking (again) about getting a Bodnar GPSDO. I've seen some scattered info on connecting this, but is there a tutorial or check list anywhere? Or will the radio just automatically use the external reference when it is connected to the 10 MHz port?

Buck ko0y
User avatar
w-u-2-o
Posts: 701
Joined: Fri Mar 10, 2017 1:47 pm

Re: GPSDO Tutorial?

Postby w-u-2-o » Wed Jul 12, 2017 5:03 pm

Hi Buck,

Yes, it's just that simple on a newer 200D. Attach a valid 10MHz signal and it will be automatically selected for use. Nearly any 10MHz signal will work, square wave, sine wave, over a wide range of input levels.

I have one of those low cost, Chinese-built GPSDOs that is marked "BG7TBL". There are probably a dozen different variants of that design available for cheap on eBay. Mine has a uBlox GPS chip and a Russian surplus OXCO inside. It was very inexpensive and it works great. It keeps everything accurate to better than a milliHertz :D

It's a bit of an extravagance for just running HF, because if you let your radio warm up to a stable temperature and calibrate it against WWV it will work plenty fine, even on JT modes. However there's just something satisfying about not having to worry about that and to know that you are perfectly accurate all the time ;)

73!

Scott
Buck
Posts: 37
Joined: Sun Apr 09, 2017 3:57 pm

Re: GPSDO Tutorial?

Postby Buck » Wed Jul 12, 2017 8:34 pm

Thanks, Scott. The digital mode I use most is quite demanding, and I thought GPS sync might help. I'm going to give it a try, either with an ebay unit, or the more expensive one from Leo Bodnar.

Buck
User avatar
w-u-2-o
Posts: 701
Joined: Fri Mar 10, 2017 1:47 pm

Re: GPSDO Tutorial?

Postby w-u-2-o » Wed Jul 12, 2017 9:00 pm

Don't forget the right kind of cables/adapters!
Buck
Posts: 37
Joined: Sun Apr 09, 2017 3:57 pm

Re: GPSDO Tutorial?

Postby Buck » Thu Jul 13, 2017 2:23 am

Oh, I have lots of adapters lying around! I decided on the Bodnar unit because it has two outputs. One I'll set at 10 MHz for the radio and the other in audio frequency to calibrate sound devices. I am wondering about the power level I should put into the 200D, however. It can be adjusted from 7.7 dBm at 8 mA to 13.3 dBm at 32 mA. What level is good for the 10MHz input? I can put a 20 dBm attenuator inline if needed.

Buck
User avatar
w-u-2-o
Posts: 701
Joined: Fri Mar 10, 2017 1:47 pm

Re: GPSDO Tutorial?

Postby w-u-2-o » Thu Jul 13, 2017 9:51 am

Run it at the maximum setting. This will get you a 3.3v square wave output signal.

I bought the Chinese unit, which was riskier, of course, because I wanted access to the uBlox GPS chip serial data output and a 1pps output, neither of which the Bodnar unit has. I did not need or want an adjustable frequency output. I also wanted an OXCO for better flywheel performance, the Bodnar unit only uses a TXCO.

It was a bit tricky to identify a version of the Chinese unit on eBay that was the correct configuration, but I managed it and actually received a unit that works beautifully.
Buck
Posts: 37
Joined: Sun Apr 09, 2017 3:57 pm

Re: GPSDO Tutorial?

Postby Buck » Thu Jul 13, 2017 1:31 pm

Good points. I have a GPS chip with antenna that I can get NMEA and PPS from if I want those. The adjustable frequency output of the Bodnar should be very useful to test links in the audio chain. Incidentally, how's it going with the block diagram for the Anan receive path? The one you made for the transmission path is in my hard-copy binder.

Buck ko0y
User avatar
Tony EI7BMB
Posts: 100
Joined: Sun Apr 09, 2017 2:31 pm
Location: Dublin
Contact:

Re: GPSDO Tutorial?

Postby Tony EI7BMB » Thu Jul 13, 2017 1:46 pm

Scott would you happen to have a URL link to the exact unit that you bought ?
User avatar
w-u-2-o
Posts: 701
Joined: Fri Mar 10, 2017 1:47 pm

Re: GPSDO Tutorial?

Postby w-u-2-o » Thu Jul 13, 2017 2:21 pm

Hi Tony,

With the understanding that I bought mine a couple of years ago, and that nothing you get from China on eBay is guaranteed, this looks to be the current listing for the same unit:

http://www.ebay.com/itm/10MHZ-Output-Sine-Wave-GPS-Displined-Clock-GPSDO-GPS-Antenna-Power-Supply-wr-/162347890705?hash=item25ccb03811:g:7qkAAOSw9eVXXT~X

The photos show the same front panel, with the same date code in the model number, the same Russian OXCO and the same uBlox GPS IC.

However, there are a variety of these on eBay. For instance, here is what looks to be an identical model from the same seller except it uses a Bliley OXCO, and for substantially less money:

http://www.ebay.com/itm/10MHZ-Output-Sine-Wave-GPS-Displined-Clock-GPSDO-GPS-Antenna-Power-Supply-wr-/162347890705?hash=item25ccb03811:g:7qkAAOSw9eVXXT~X

As you can see, the board is designed to accept a variety of OXCOs. I like very much that this seller is providing photos of the board configurations, it seems pretty legit. Since I'm not interested in lab grade accuracy, I'd probably go for the less expensive one.

I'd shy away from the Trimble based units. The uBlox chips are by far the superior performers. I spec. them for my work designs.

If you shop carefully on eBay, you'll also find 10MHz distribution amplifiers from the same Chinese sources, if you need to distribute the 10MHz to multiple radios or instruments.

Let us all know if you get one, and what you think of it.

Note: when you use an OXCO based GPSDO you must be patient for the oscillator oven to stabilize. The Bodnar unit will come up and say it's locked in seconds. With an OXCO based unit walk away for 30 or 60 minutes and then come back to check on it. That's also why the OXCO units have much better hold-over performance than the TXCO units, the OXCOs won't drift hardly at all when GPS signal is lost. I just have my puck antenna sitting on a window sill and it works great.

73,

Scott
User avatar
w-u-2-o
Posts: 701
Joined: Fri Mar 10, 2017 1:47 pm

Re: GPSDO Tutorial?

Postby w-u-2-o » Thu Jul 13, 2017 2:31 pm

Here's an example (just a tiny, tiny example, it does so much more than this) of the kind of data that uCenter will give you when you are using a uBlox based unit. uCenter can provide you with so many statistics and graphs it'll keep you busy for days!

Image

73!

Scott
User avatar
w-u-2-o
Posts: 701
Joined: Fri Mar 10, 2017 1:47 pm

Re: GPSDO Tutorial?

Postby w-u-2-o » Thu Jul 13, 2017 2:40 pm

Might as well post the NTP info. while I'm at it, and we can turn this into a "sticky" thread for the next person looking for GPSDO data... :)

If you have a GPS with a serial port for NMEA data and 1PPS output, there is version of the Windows NTP software that can make use of it quite effectively. The 1PPS needs to be properly buffered and attached to the DCD pin of that serial port. Excellent instructions for doing this can be found here:

http://www.satsignal.eu/ntp/NTP-on-Windows-serial-port.html

and

http://blogs.cae.tntech.edu/jwlangston21/2009/12/07/installing-and-using-ntp-with-a-garmin-18-gps-with-pps/

Windows time accuracy will be submillisecond and you won't be dependent on the internet for super accurate time in your PC. Using Meinberg NTP and normal internet NTP I'm "only" getting +/-2mS with occasional excursions to <20mS ;)

As discussed above, I purchased one of the inexpensive, Chinese-made BG7TBL GPSDO units off of ebay (just search ebay for "gpsdo", there are lots of them and many variants). There is an excellent analysis of their performance with the Russian OXCO here:

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

This thing has been the cat's meow. I've got its 10MHz output attached to my ANAN series radios and they have been rock solid. I just checked the serial port using:

http://www.satsignal.eu/software/net.htm#SerialPortLEDs

and confirmed a valid 1 PPS signal on the CTS pin. It would be a simple matter to move that over to the DCD pin to use with the above referenced NTP software.

I've also confirmed a valid data stream from the unit using u-blox uconnect software, as you can see in my post above. This is, unfortunately, a u-blox binary data stream, however you can hack the unit to obtain an NMEA stream for NTP from a management serial interface internal to the unit. Again it's a simple exercise to rewire the existing serial port or add a second one. Start reading this page and the next of this thread here:

http://www.eevblog.com/forum/testgear/bg7tbl-gpsdo-master-reference/75/

73!

Scott/w-u-2-o
User avatar
Tony EI7BMB
Posts: 100
Joined: Sun Apr 09, 2017 2:31 pm
Location: Dublin
Contact:

Re: GPSDO Tutorial?

Postby Tony EI7BMB » Thu Jul 13, 2017 7:58 pm

Excellent Scott, thanks for all the info
Buck
Posts: 37
Joined: Sun Apr 09, 2017 3:57 pm

Re: GPSDO Tutorial?

Postby Buck » Sat Aug 05, 2017 1:18 am

I decided after all to get one of the Chinese units from ebay, and it seems to work well. I test it by zooming in on WWV and centering the carrier on the panadapter, and 3 mHz was what I measured. If there is a better way, I would like to know of it.

I think that what I call the "crazy mouse" problem should be mentioned. Windows might see the GPS data over the serial port as a kind of mouse, and start randomly moving and clicking your pointer. Very annoying. The solution is to unplug the GPS, go to device manager, find something called a "serial ball point mouse," and disable that.

Buck ko0y
User avatar
w-u-2-o
Posts: 701
Joined: Fri Mar 10, 2017 1:47 pm

Re: GPSDO Tutorial?

Postby w-u-2-o » Sat Aug 05, 2017 1:37 am

3 milliHertz? Dude, I don't know how anyone is going to understand you when you are so far off frequency! ;)

Did you get the Chinese unit with the Russian OXCO?

Incredible value, those Chinese units, eh?

73!

Scott
Buck
Posts: 37
Joined: Sun Apr 09, 2017 3:57 pm

Re: GPSDO Tutorial?

Postby Buck » Sat Aug 05, 2017 12:12 pm

w-u-2-o wrote:3 milliHertz? Dude, I don't know how anyone is going to understand you when you are so far off frequency! ;)

Did you get the Chinese unit with the Russian OXCO?

Incredible value, those Chinese units, eh?

73!

Scott


I haven't opened it up yet but the posted photos showed CTS OXCO. These are great bargains, I agree. The active antenna cord is long enough to run outside to a corner wall where it locks on 8 or so satellites.

Next up is to set up ntp. Did you need, on your unit, to connect the PPS output to pin 1 on the RS232 and if so is it necessary to change the voltage levels?

Buck
User avatar
w-u-2-o
Posts: 701
Joined: Fri Mar 10, 2017 1:47 pm

Re: GPSDO Tutorial?

Postby w-u-2-o » Sat Aug 05, 2017 5:11 pm

Buck,

I did not implement a local NTP capability. Just follow the directions at the links I provided above. They very clearly describe what signals have to be on what pins.

I do not believe that you need to do any level translation of the 1PPS output on these BG7TBL design units. Using the "Serial Port LEDs" utility (scroll to the bottom of the link) I was able to see the 1PPS signal coming out of the GPSDO just fine.

73,

Scott
Buck
Posts: 37
Joined: Sun Apr 09, 2017 3:57 pm

Re: GPSDO Tutorial?

Postby Buck » Mon Aug 07, 2017 1:33 pm

w-u-2-o wrote:
I just checked the serial port using:

http://www.satsignal.eu/software/net.htm#SerialPortLEDs

and confirmed a valid 1 PPS signal on the CTS pin. It would be a simple matter to move that over to the DCD pin to use with the above referenced NTP software.

Scott/w-u-2-o


One would think so, however... I made an adapter to run pins 2-7 and 9 straight through, and route pin 8 to pin 1. On my scope, I get a nice square wave from -7.4 to 7.4 volts, well within RS232 specs, on pin 8 without the adapter and pin 1 with. Incidentally, the BNC 1 PPS output is zero to 3 volts with same shape wave.

In u-center, with adapter attached, I see the GPS data and can modify port rate, so TXD and RXD work, but no indication of PPS. Using Serial Port LEDs, I get flashing on CTS with no adapter, but no flashing on DCD with adapter. Same indications with realTerm on Windows, and CoolTerm on the mac. So PPS is present at the serial port, but not making it through the usb adapter. It's an FTDI adapter, not Prolific.

I have few ideas about why this doesn't work. USB is defective on that one pin only? The drivers for these adapters have been programmed to ignore DCD? Any other possibilities?

Buck ko0y
User avatar
w-u-2-o
Posts: 701
Joined: Fri Mar 10, 2017 1:47 pm

Re: GPSDO Tutorial?

Postby w-u-2-o » Mon Aug 07, 2017 5:04 pm

If you can't read DCD, then it sounds like a problem with either the USB adapter hardware, driver, or both.

Time for a new one!

I use a Moxa N-port serial to Ethernet device server and can see my serial devices from any computer on the network (with properly set up drivers, of course). There are usually good deals on Moxa units on eBay from time to time.

73,

Scott
Buck
Posts: 37
Joined: Sun Apr 09, 2017 3:57 pm

Re: GPSDO Tutorial?

Postby Buck » Mon Aug 07, 2017 5:47 pm

w-u-2-o wrote:If you can't read DCD, then it sounds like a problem with either the USB adapter hardware, driver, or both.

Time for a new one!

I use a Moxa N-port serial to Ethernet device server and can see my serial devices from any computer on the network (with properly set up drivers, of course). There are usually good deals on Moxa units on eBay from time to time.

73,

Scott


Driver, I think. I installed serialpps.sys, edited the registry, and set the local environment variables, all as indicated. But Windows 10 will not load the serialpps driver to that device, and will not let me install it manually. I'll look into the Moxa adapters.

Buck ko0y
Joe-W4WT
Posts: 15
Joined: Sun Apr 09, 2017 5:27 pm
Location: Cumming, GA

Re: GPSDO Tutorial?

Postby Joe-W4WT » Thu Aug 10, 2017 9:55 pm

Hi Scott,

I just puchased one of these from your link. Thanks for posting it. Looks like mine is newer based on the board date which is late last year and the date on the front of the unit shows 3/29/2017.

The circuit boards appears different from the pictures I saw of the unit previously. It does have the BLOX unit. I just got it running and haven't tested anything other than lock (in the basement already!) and if it works with my Hybrid 8000/200D combo and it does. More info as I find out what it can do. Here's top and bottom pics of the board below.

73,

Joe W4WT

Image
Image
User avatar
w-u-2-o
Posts: 701
Joined: Fri Mar 10, 2017 1:47 pm

Re: GPSDO Tutorial?

Postby w-u-2-o » Thu Aug 10, 2017 10:13 pm

Welcome to the hyper-accurate crowd, Joe! :)
Buck
Posts: 37
Joined: Sun Apr 09, 2017 3:57 pm

Re: GPSDO Tutorial?

Postby Buck » Sun Aug 13, 2017 1:57 pm

w-u-2-o wrote:If you can't read DCD, then it sounds like a problem with either the USB adapter hardware, driver, or both.

Time for a new one!

I use a Moxa N-port serial to Ethernet device server and can see my serial devices from any computer on the network (with properly set up drivers, of course). There are usually good deals on Moxa units on eBay from time to time.

73,

Scott

Scott, does your MOXA serial-to-ethernet pass signals on DCD? It appears that many of these converters only pass TXD and RXD.

Buck ko0y
User avatar
w-u-2-o
Posts: 701
Joined: Fri Mar 10, 2017 1:47 pm

Re: GPSDO Tutorial?

Postby w-u-2-o » Sun Aug 13, 2017 5:43 pm

That is true, Buck. You have to obtain an appropriate device server from the rather large set of choices that Moxa provides.

I have a 5450I. It faithfully carries all 9 signals on a standard 9 pin serial port. I use one port for my KPA500 amplifier and the other for the BG7TBL GPSDO. And two spare ports for future requirements, of course.

73,

Scott
User avatar
N7CVZ
Posts: 5
Joined: Sun Apr 09, 2017 2:33 pm
Location: Corbett, Oregon USA

Re: GPSDO Tutorial?

Postby N7CVZ » Tue Aug 15, 2017 1:57 am

Can someone tell me the difference between the ones on eBay. they range from 135-185. THE LINK FOR THE ONE ABOVE IS 185?
User avatar
w-u-2-o
Posts: 701
Joined: Fri Mar 10, 2017 1:47 pm

Re: GPSDO Tutorial?

Postby w-u-2-o » Tue Aug 15, 2017 2:09 am

IMHO, you want one of the BG7TBL versions. These use the uBlox GPS chip, which is far superior to the Trimble units, and others.

The price variations among the BG7TBL units are primarily driven by which OXCO they use. The higher performing OXCO's cost more.

The reality is that any OXCO will provide more than sufficient performance for keeping your radio exactly on frequency. Any of the BG7TBL versions should work just fine.

All that said, remember that when you order something that comes directly from China on eBay you are taking a chance on getting bad product, not getting any product, or a huge hassle trying to return bad product. So far I have ordered four things for delivery directly from China and only had a problem with one of them (it was not the GPSDO). Your mileage may vary, caveat emptor, and all that jazz!

73!

Scott

Return to “Everything Else: Antennas, Relays, Switches, Power, Grounding, Cooling, etc.”