Re: [time-nuts] Trimble Thunderbolt E frequency pulling
Al, Thanks for the good idea, that would certainly have saved me a bit of work:-), but the switch box inserted in the coax line with the counter input set to high impedance performs the same function, straight through connection with the option to switch in a 50 ohm shunt resistor, and it's quite clear that the frequency shift is virtually instantaneous. Nigel GM8PZR Nigel, Set your counter to high impedance. Then install a T connector on the input. Then you can install or remove a 50 ohm terminator on the T while plotting the results. Then you can see how fast the frequency shift is depending on the load. AL, k9si ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Trimble Thunderbolt E frequency pulling
Nigel, Set your counter to high impedance. Then install a T connector on the input. Then you can install or remove a 50 ohm terminator on the T while plotting the results. Then you can see how fast the frequency shift is depending on the load. AL, k9si Switching the impedance at the counter itself resets any plot that's in progress, which does introduce some delay, so I put together a small switch box that could be inserted into the coax and confirmed it's a rapid effect that's unlikely to be thermal. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Trimble Thunderbolt E frequency pulling.
My bet is interaction of the load current and power supply with the EFC and/or OCXO - Well, I haven't started probing the hardware yet, I was hoping I might get some confirmation first as to whether what I I'm seeing is an anomaly for this one or just par for the course with the Tbolt E, but as far as Lady Heather indicates there's no step change in the EFC that matches the frequency change, rather a gradual change after the event as the conditioning seeks to correct the displacement. Nigel GM8PZR ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] Trimble Thunderbolt E frequency pulling.
My bet is interaction of the load current and power supply with the EFC and/or OCXO. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Trimble Thunderbolt E frequency pulling.
> Before I start probing any deeper I'd be interested to hear if anyone > else come across this with the Thunderbolt E. Is it thermal? Can you measure the frequency shift before it has time to warm up? Switching the impedance at the counter itself resets any plot that's in progress, which does introduce some delay, so I put together a small switch box that could be inserted into the coax and confirmed it's a rapid effect that's unlikely to be thermal. It's even more observable with disciplining turned off and there's no attempt to correct it, I can toggle back and forth between the two frequencies just by switching the load. One thing I did get wrong though when transposing my notes, switching from low to high impedance at the 10Mhz output will increase the frequency, with high to low decreasing it again, which is the reverse of what I originally posted...whoops:-) Nigel GM8PZR ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] Trimble Thunderbolt E frequency pulling.
Please note that this question refers to the branded "Thunderbolt E" GPSDO, in a silver coloured case with blue label and using a single 24V supply, and not the gold coloured "Thunderbolt" that is often found marked "Rev E". Whilst testing a Thunderbolt E I've observed that the frequency of the 10MHz output is affected by the load impedance. Switching a counter input impedance from 50ohms to 1Mohm for example will decrease the frequency around 1 part in 10^9, and this is reflected in a consequent increase in the DAC voltage over the course of a few minutes with the frequency recovering at the same time. Similarly, with the frequency steady with a 1Mohm load, switching to 50ohms will increase the frequency by a similar amount with the DAC voltage decreasing to provide correction. I'm familiar with the concept of frequency pulling in oscillators but would have expected the Thunderbolt E output to be better buffered than this, it's certainly not something I've experienced with the gold cased Thunderbolts. Before I start probing any deeper I'd be interested to hear if anyone else come across this with the Thunderbolt E. Regards Nigel GM8PZR ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Trimble Thunderbolt E frequency pulling.
> I'm familiar with the concept of frequency pulling in oscillators but > would have expected the Thunderbolt E output to be better buffered than > this, it's certainly not something I've experienced with the gold cased > Thunderbolts. > Before I start probing any deeper I'd be interested to hear if anyone > else come across this with the Thunderbolt E. Is it thermal? Can you measure the frequency shift before it has time to warm up? -- These are my opinions. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
