External GPSDO not accepted be Flex 6500.

ai6re

I am unable to get the Flex 6500 to use an external GPSDO on the external 10 MHZ input. I am supplying a 5 dbm signal to the radio. When I check the frequency accuracy of the radio it shows -7hz on 14.1mhz which is the TCXO in the radio. My frequency counter is using the GPSDO for its clock so if the radio uses the same signal it would have to show the exact frequency. Do I have to Install the GPSDO option in the 6500 GPS Setup Tab for it to use an external clock? Don

K6OZY

If i recall, the radio only checks for external GPSDO at power up.

Ned K1NJ

Yes, it checks for the 10 MHz input first if a GPSDO is not installed, then defaults to the internal oscillator if it's not found. There is some confusion concerning the 10 MHz input connector. The on-line pdf shows it in a different place than on the actual rear panel. So make sure the correctly labelled connector on the panel is the one you are using. My 10 MHz source worked immediately with no fuss. The radio just finds it and uses it.

ai6re

Ned, I am using the one labled on the radio as 10mhz in. It is the top left RCA on my 6500. Do you know what level signal you are providing to the input? I did not want to overload it so I am just sending 5dbm. I have powered off and removed the power to the radio but it still shows the TCXO in use. How do you know it is using the external signal? Regards, Don...

ai6re

I just raised the GPSDO signal to 6dbm and the radio switched to the external clock and is working fine. It now shows exactly on frequency with the GPS so the solution is to update the spec for external clock signal to 6dbm for dependable external use. This problem can be closed as an update to the specification for external clock signal level. Thanks, Don

ai6re

I was mistaken. The problem remains and at 50mhz the TCXO shows -24hz so the radio is still not using the external signal. This is the same amount of error I see with both Rubidium Clock and GPSDO calibrated frequency counter. My questions remain: Am I using the correct socket; top left RCA next to the ACC DB15)? If others have this working then how do they verify the radio is using their external signal? What is the signal level being used when it works?

Ned K1NJ

Don, When I first tried the radio I didn't an Rb source. The radio was "off" by 5 or 10 Hz. at 10 MHz WWV. I asked about the calibration method to get the frequency zeroed, but was told that would probably come along in a future release. Then I added the Rb standard. I don't know its exact output power, but it's < 10 dBm. I checked frequency by using two slices listening to WWV but offset by a fixed amount e.g. 500 Hz. I use one slice USB and the other LSB so each hears the same note and listen to the beat. This would work with any stable signal I suppose. Without the 10 MHz reference, its off several Hz. With the reference the note sounds more like a phase shift and is well under 0.1 Hz. The connector seems to be the same one you are using, upper row, next to the acc'y connector near the middle of the panel.

Graham-KE9H

Don: 1.) The red RCA type connector at the upper left of the RCA connector cluster is the correct input port for an external 10 MHz Input. It is properly labeled on all production radios. 2.) The level must be a MINIMUM of +4 dBm for the input to function. This is 1.0 Volt peak to peak. It will work with either sine or square wave inputs, although a sine wave input will be quieter with respect to 10 MHz harmonics. 3.) The radio will only look at the 10 MHz input for input selection while it is booting, so you will need to reboot the radio after providing the proper input signal, before it will start using it. If the signal disappears while the radio is running, it will switch back to one of the internal sources, but will not attempt to re-select the external 10 MHz input until the next time the radio is booted (turned off then back on, or power cycled.) If this does not work for you, please contact service / support. --- Graham / KE9H ==

ai6re

Graham, You had the information I needed to get this working. 1 volt across 50 ohms is .02 watts or 13dbm. That is almost 8 times the power of 5 dbm at 50 ohms, stated on an earlier post to the community by Tim. Once I provided the 13dbm signal to the radio it works perfectly and the counter shows exactly the same as the radio. This problem can be closed as an update to the specification for external clock signal level to a 13dbm / 50ohm or 1 Volt peak to peak sine or square wave.. Thanks, Don

Graham-KE9H

Don: I am glad to hear you are up and running. Assuming a sine wave: 1 Volt peak-to-peak (the minimum input) is 0.357 V RMS is 0.002 Watts or 4.1 dBm into 50 Ohms. 1 Volt RMS is 2.8 Volts peak-to-peak is 0.02 Watts or +13 dBm into 50 Ohms. To convert from peak-to-peak to RMS for a sine wave, divide by 2.8. It is the RMS value you use to calculate power in P=E^2/R or the dBm power calculations. Either level should work. The acceptable input level is 1 Volt peak-to-peak up to 3.3 Volts peak-to-peak. Into 50 Ohms, this would be about +4 dBm to about +15 dBm. Best regards, --- Graham /KE9H ==

ai6re

Graham, Thanks for the correction to my measurments. You are certainly correct in using the RMS value and I now understand the error in my measurements. I was just using a scope and a variable attenuator and forgot some long ago education on power. Thanks, Don... AI6RE

John Watson W4JCW

How can one tell if the external GPSDO is actually working...I have the Leo Bodnar installed on my 6500, but not sure if it actually works?

KD0RC

Hi John, go to Settings, Radio, RX tab (I think... I am not at my radio to verify). In any event, find the tab that shows the calibration screen. That will tell you if the GPSDO is controlling or if it is the internal TCXO.

KD0RC

Hi John, I am back at my radio now. On my 6400, I have the following screen that shows me the state of my GPSDO. Your 6500 display may be slightly different. I leave my choice on Auto and it finds the GPSDO when I am operating from home. When I am operating portable from my 5th wheel camper, it automagically switches over to TCXO. At that point I need to run a calibration (i.e. click the Start button).

Note that my offset shows -5 ppb. That is because I ran the calibration while the GPSDO was connected. Normally you should just zero out this field without running a cal. Note also that I live 50 miles south of WWV in Ft. Collins, so 2.5 MHz is my best cal frequency, day or night. Depending on your location and time of day/year, you may be better off with 5, 10, 15 or 20 MHz (find the strongest one before doing a cal, then enter that in the Cal Frequency box).

If I force it to use the TCXO and then click the Start button, you can see that it applied a -1122 ppb correction to the internal oscillator.

Before I got my GPSDO, I ran the calibration quite frequently to see if there was any appreciable drift in the TXCO, and although I did not do a real scientific investigation with charts, graphs and color glossy photographs, I did not see much variation over time. I concluded that the TCXO is quite stable and does not need re-calibration on too frequent a basis. If your shack temps vary wildly, you might want to do more re-calibrations.

Once you connect a GPSDO, calibrations are not necessary at all, unless you want to verify that the GPSDO is actually working. I think that an offset value of less than 10 would show that the GPSDO is doing its job. I typically get values from 0 to -5 when I run my Leo Bodnar unit. Last year, it came up with -5. I re-ran it today and got -3. All perfectly normal and shows that the GPSDO and the radio are working correctly in this regard. 3 ppb is .003 Hz at 1 MHz, and 1122 ppb is only 1.22 Hz at 1 MHz so you can be quite sure that you are on frequency with this radio!

WX7Y

Len, the older Flex Radios like the 6500 and 6700 ARE different then the 6400 or 6600, they have NO Selection option for the TCXO or External Reference.

Here is how you tell if the External GPS is working on a Flex 6500,

1st with the GPS 10MHZ unplugged got to setup then to the RX tab, set the CAL frequency to 10 MHz, then click "Start". Write down what the Offset in Frequency (ppb) is.

2nd Turn off the Flex6500 and plug the external GPS 10MHz source in and turn the radio back on and run the test again making sure the calibration frequency is set to 10MHz and see what the difference is for a reference mine is at -3 (ppb) "Parts per billion" The TCXO will be a lot high offset frequency.

The thing with the older series of radios if the GPS goes off the radio WILL switch back to the TCXO frequency BUT will not switch back if the GPS 10MHz is restored unless the radio is turned off and back on.

I tested using the "GPS Install" and the 6700 shut off and back on

The 6600 and 6400 will restore automagically switch back if the external GPS 10MHz is restored with out powering them down.

This may have changed over the years but in almost 10 years of using my Flex 6700 that is how it's been done.

Screen shot of a Properly working External 10MHz GPS

Screen shot AFTER I did a GPS Install command, Reads ZERO data from the External GPS and can be left UNINSTALLED because this is for the Flex Internal GPS.

KD0RC

Thanks Bret. I knew that they are not exactly alike, but wasn't sure what the differences are.

So John, does it all make sense now?

WX7Y

No problem Len, just so we get the user going in the right direction so they don't get confused.

It helps when you've had both versions of hardware I think and done it before, not much help on the newer radios anymore beyond what I can remember, I sold the Flex6600M and picked up a very clean 6700 so both radio now are F6700's.

73

Bret WX7Y