GPSDO Tutorial?

[PaulManc]

200D, 7000, 8000, Andromeda, and G2 all use the same 10MHz input circuit. You should have no problem.

Forgive me for asking again, Scott.

What should the input impedance of the 10mhz ref input be is it 50ohms or something else? I plan to use the Leo Bodnar GPSDO

Cheers,

[w-u-2-o]

The Bodnar is 50 ohm output impedance and the ANAN is high impedance as delivered from the factory. Nevertheless that combo should work just fine as is. You may have to adjust the Bodnar drive level.

[W9BHI]

There is a 2 pin header on the board that places a 50 ohm termination on the external ref.input.

[KC2QMA]

I have the one with the 2 10mhz outputs and this unit and works fine with G2.
It works with as little as 8mA of drive, outputs a square wave.
Just put the GPS antenna in your window or outside, connect GPSDO to radio via BNC to SMA cable to the 10mhz input on the back of the radio go into Thetis and enable External Reference and your done!
simple plug and play!

[PaulManc]

The Bodnar is 50 ohm output impedance and the ANAN is high impedance as delivered from the factory. Nevertheless that combo should work just fine as is. You may have to adjust the Bodnar drive level.

As usual, BIG Tnx 73

[KA9UVY]

I have been experiencing since day one my Anan 7000DLE MKIII locking in two different places when powered on, I typically just run a calibration with WWV in Thetis to resolve the issue and it stays OK most of the time but very seldomly jumps back off again the correction or offset is to around 0.99997656 instead of 10.000001 or so.
Anyway I had purchased a Leo Bodnar GPS 10 Mhz source many months ago but with limited time to spend with my ANAN, I just hooked it up tonight.
My Results:
Radio is off frequency by this same margin when observing WWV but I cannot seem to enter a correction factor into HPSDR when use ext source is checked?
Pardon me for not seeing much of anything on here about using an ext source and still applying a correction factor in Thetis to get everything to be correct.?
Thetis defaults to 1.00000000 if I check the ext source and I can see the WWV carrier jump to the left of the center crosshair then my radio is clearly off frequency. It looks like I need a correction factor applied to my ext source to get this radio ON freq and hitting the reset button does nothing.
My Leo Bodnar software panel is pretty much exactly the same as the one posted earlier in this thread.
Please point me in the right direction. Thanks

[W4WT]

Robert, I assume you have tried adjusting the adjustment that is just below the option "Using ext 10Mhz ref" and not the "Correction Factor" adjustment when you have the GDO connected? I have a 7000 MK II and I use a GDO and have no trouble moving the "zero" around with the adjustment factor in the bottom left of the Calibration Tab. My correction is small but it did take just a bit to zero it to WWV with my GDO; 1.00000003. You shouldn't hit the reset button after entering your offset unless you want to clear it.

I'm assuming you have the Thetis version with this correction area in the Calibration tab. I don't remember which version it came out in. Before that version, there was only the "Correction Factor" window which I don't believe affected the external input at all.

Joe, W4WT

[KA9UVY]

Hi Joe, Thanks for the reply, the version I am running is listed in my signature and I believe its the newest out or close.
My calibration section is as follows:

freq cal.jpg (135.84 KiB) Viewed 5262 times

When I check to use the external 10 Mhz Ref, It will not change if I move the correction factor up or down and it actually reverts back to 1.0000000

If I calibrate with WWV it adjusts and stays put but my radio sometimes jumps off.
I can't use my GPSDO at all with out a correction factor in HPSDR?

[W4WT]

Robert, you may have already tried this but if not give it a go. Save your current database then reset the database and shutdown Thetis. Power cycle the radio then start Thetis. Put just the bare minimum setup info in to get the radio operating and then try the calibration routine again and see if anything changes. If it still fails, reload your database.

This actually sounds like a hardware problem to me. Assuming the database reset doesn't change anything, I would think that even more strongly.

You say it sometimes "jumps", I assume you mean it jumps frequency? If so, how much does the frequency change? Does it ever jump back?

Joe, W4WT

[W9BHI]

I have a 7000DLE blue face and I am using a Trimble Thunderbolt GPS unit as an external 10MHz reference. It has a sine wave output that was a bit too high so I have the 50 ohm jumper installed on the Orion board and it is now within spec. Thetis is configured with the external 10 MHz enabled. I don't use any offsets because the GPS output is a near perfect 10 MHz and when I check against 10MHz WWV with the mode set to DSB and looking at the phase mode, it is right on frequency. Mind you that my radio was an earlier one that would not recognize a sine wave input on the 10 MHz reference input.
I had the radio in to Doug for a 12 meter output issue and while he had it on his bench, he changed a resistor value in the external reference detection circuit that fixed the issue with it not detecting a sine wave. He notified the factory about the issue and all units after that last run were using the recalculated resistor in that circuit.

[VK4BXI]

Tests that I've done imply that the 10MHz signals from the GPS satellites are changing frequency randomly by small amounts.

I've been using an "old" but very stable reference 10 MHz crystal oscillator which is in its own oven to supply the 10 MHz external reference to my 7000 mkII. For some reason or another I had doubt sown in my mind about its accuracy.

I found an old Datachron network time server which has a GPS disciplined 10 MHz reference and set that to work. I then purchased a GPSDO by VK4AMG (which is designed as a ultra stable reference for microwave use) and set that running.

Using the reference oscillator as an external trigger I then connected the two GPSDO's to the two inputs of my 100MHz scope.
I allowed everything to settle for a day or so and then looked at how the two traces were moving around. At times both traces were almost "rock" stable and moved together against the 10MHz crystal oscillator at a very low rate.....taking some 50 ~60 seconds to move a complete sine wave across the screen, indicating that my crystal oscillator was "spot on".
The surprise came when one or other of the GPSDO's abruptly changed frequency by about 0.05 to 0.1 Hz and stayed that way for a few minutes. At times both were "off" ....and in different directions. The changes appear to be "random".

I am coming to believe that either this is deliberate or a function of how the GPSDO's operate handing over from one satellite to another. I wonder if anyone else has noticed this or has an idea of what is going on ?

Bob

[w-u-2-o]

Tests that I've done imply that the 10MHz signals from the GPS satellites are changing frequency randomly by small amounts.

I can assure you this is not the case. I have been deeply involved with the GPS and, in particular, GPS time and frequency standards, since before GPS reached it's Initial Operating Capability (IOC) in 1993.

Using the reference oscillator as an external trigger I then connected the two GPSDO's to the two inputs of my 100MHz scope.
I allowed everything to settle for a day or so and then looked at how the two traces were moving around. At times both traces were almost "rock" stable and moved together against the 10MHz crystal oscillator at a very low rate.....taking some 50 ~60 seconds to move a complete sine wave across the screen, indicating that my crystal oscillator was "spot on".

Those interpretations are exactly backwards. The two GPSDO outputs moved together, which means they are doing what they are supposed to, which is to generate highly accurate and identical 10MHz signals. It's the crystal oscillator that was not as close to 10MHz as the two GPSDOs. Trigger off of the GPSDO and watch the crystal oscillator output "move". The fact that both GPSDOs were locked together is a clear indications things were working as they should be.

The surprise came when one or other of the GPSDO's abruptly changed frequency by about 0.05 to 0.1 Hz and stayed that way for a few minutes. At times both were "off" ....and in different directions. The changes appear to be "random".

This is caused by a faulty or poorly designed GPSDO, and not any fault or design issue with GPS. Which GPSDO demonstrated instability, the Datachron or the VK4AMG unit?

I am coming to believe that either this is deliberate or a function of how the GPSDO's operate handing over from one satellite to another. I wonder if anyone else has noticed this or has an idea of what is going on ?

There is no "hand over" in GPS, it does not work like a cellular radio system. As the constellation in view changes the solution for frequency will not change appreciably and if there are short time periods (seconds, not minutes) where a solution is not available (unlikely unless you are in deep urban or natural canyons) the short term stability of the oscillator that is being disciplined is sufficient to maintain a very high level of accuracy. And, in a properly designed GPSDO, that oscillator will start to drift in the absence of a good GPS solution, but it should NEVER jump.

Again, I can 100% assure you GPS time and frequency transfer are far superior to your crystal oscillator and there are no "random frequency changes". The same is true for all extant GNSS systems including BeiDou, GLONASS and Galileo. Your experiments need to use a GPSDO as the master reference, and it appears you have at least one bad or poorly designed GPSDO.