Re: [time-nuts] DMTD: Mixer DC offset will result in time offset at zero-crossing detector out?
1st section is common mode low pass filter, 2nd section is differential common mode low pass filter. Ok - makes sense now. Yes AC coupling after limiting isnt such a good idea. AC coupling either between the mixer and the input stage of the limiter chain or after the last linear stage would be better. I assumed so, since limiting an offset sinusoid will produce an asymmetrical trapezoid which will have a different mean value than the original sinusoid. But, I wasn't sure so thanks for confirming this. On 23 November 2013 07:28, Bruce Griffiths bruce.griffi...@xtra.co.nzwrote: WarrenS wrote: Stephan Did you also notice that the AC coupling is done **after** the sine wave has already been clipped by the previous stage (according to the schematic note)? This generally is not a good way to remove DC offset from a low level 'noisy' signal. I doubt that Bruce was recommending doing it that way. ws Yes AC coupling after limiting isnt such a good idea. AC coupling either between the mixer and the input stage of the limiter chain or after the last linear stage would be better. Bruce - Original Message - From: Stephan Sandenbergh ssandenbe...@gmail.com To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Friday, November 22, 2013 4:19 AM Subject: Re: [time-nuts] DMTD: Mixer DC offset will result in time offset at zero-crossing detector out? Hi, Thanks - mystery solved. This is one of the systems that I looked at, and missed the DC block in the second amplification stage. I guess it is possibly a large Ceramic 10uF. My bad. Thank you for putting up those web pages I find them to be very good references. I spent quite a lot of time reading through them. Something that puzzles me though is your mixer termination ( http://www.ko4bb.com/~bruce/LowNoiseMixerPreamp.html). What is the logic in having the second balun (and connected in that way)? Regards, Stephan. On 22 November 2013 13:15, Bruce Griffiths bruce.griffi...@xtra.co.nz wrote: Stephan Sandenbergh wrote: Hi, I'm playing with dual-mixer time difference stuff again. And, came across this and I find it somewhat puzzling since no one else seems to have encountered it. Possibly because I'm missing something? The doubly balanced mixers (of the type known to be used in DMTDs and phase noise measurement systems) are known to have DC offsets. So much so that the guys doing phase noise measurements employ elaborate DC removal circuits in their preamps to combat this. Here's my question: why isn't this DC offset removed in any DMTD circuits I've seen? It seems standard practice to attach the filtered mixer output directly to the zero crossing detector. I did a quick simulation (see attached): The mixer beat is a 10Hz sine 0.7Vpp. If you then use a Collins style zero crossing detector the first stage will have a small gain (I chose a gain of 2.83 from Bruce Griffiths pages ( http://www.ko4bb.com/~bruce/ZeroCrossingDetectors.html)). I then compare this ideal signal to that of a similar one that is offset by 40mV. Notice the asymmetry in the signal due to offset. 40mV result in 1.8ms offset 4mV result in 180us offset Obviously, once the time offset is there no amount of subsequent slope amplification will remove it. I've tested this in practice and bingo, I now have a very accurate way of plotting relative mixer DC offset over time. Any comments? ___ 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. One can always add AC coupling to eliminate this effect as in http://www.wriley.com/A%20Small%20DMTD%20System.pdf Bruce ___ 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 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 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 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] DMTD: Mixer DC offset will result in time offset at zero-crossing detector out?
Hi, I'm playing with dual-mixer time difference stuff again. And, came across this and I find it somewhat puzzling since no one else seems to have encountered it. Possibly because I'm missing something? The doubly balanced mixers (of the type known to be used in DMTDs and phase noise measurement systems) are known to have DC offsets. So much so that the guys doing phase noise measurements employ elaborate DC removal circuits in their preamps to combat this. Here's my question: why isn't this DC offset removed in any DMTD circuits I've seen? It seems standard practice to attach the filtered mixer output directly to the zero crossing detector. I did a quick simulation (see attached): The mixer beat is a 10Hz sine 0.7Vpp. If you then use a Collins style zero crossing detector the first stage will have a small gain (I chose a gain of 2.83 from Bruce Griffiths pages ( http://www.ko4bb.com/~bruce/ZeroCrossingDetectors.html)). I then compare this ideal signal to that of a similar one that is offset by 40mV. Notice the asymmetry in the signal due to offset. 40mV result in 1.8ms offset 4mV result in 180us offset Obviously, once the time offset is there no amount of subsequent slope amplification will remove it. I've tested this in practice and bingo, I now have a very accurate way of plotting relative mixer DC offset over time. Any comments? attachment: Time offset due to mixer DC offset (40mV).png___ 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] DMTD: Mixer DC offset will result in time offset at zero-crossing detector out?
Stephan Sandenbergh wrote: Hi, I'm playing with dual-mixer time difference stuff again. And, came across this and I find it somewhat puzzling since no one else seems to have encountered it. Possibly because I'm missing something? The doubly balanced mixers (of the type known to be used in DMTDs and phase noise measurement systems) are known to have DC offsets. So much so that the guys doing phase noise measurements employ elaborate DC removal circuits in their preamps to combat this. Here's my question: why isn't this DC offset removed in any DMTD circuits I've seen? It seems standard practice to attach the filtered mixer output directly to the zero crossing detector. I did a quick simulation (see attached): The mixer beat is a 10Hz sine 0.7Vpp. If you then use a Collins style zero crossing detector the first stage will have a small gain (I chose a gain of 2.83 from Bruce Griffiths pages ( http://www.ko4bb.com/~bruce/ZeroCrossingDetectors.html)). I then compare this ideal signal to that of a similar one that is offset by 40mV. Notice the asymmetry in the signal due to offset. 40mV result in 1.8ms offset 4mV result in 180us offset Obviously, once the time offset is there no amount of subsequent slope amplification will remove it. I've tested this in practice and bingo, I now have a very accurate way of plotting relative mixer DC offset over time. Any comments? ___ 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. One can always add AC coupling to eliminate this effect as in http://www.wriley.com/A%20Small%20DMTD%20System.pdf Bruce ___ 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] DMTD: Mixer DC offset will result in time offset at zero-crossing detector out?
Hi, Thanks - mystery solved. This is one of the systems that I looked at, and missed the DC block in the second amplification stage. I guess it is possibly a large Ceramic 10uF. My bad. Thank you for putting up those web pages I find them to be very good references. I spent quite a lot of time reading through them. Something that puzzles me though is your mixer termination ( http://www.ko4bb.com/~bruce/LowNoiseMixerPreamp.html). What is the logic in having the second balun (and connected in that way)? Regards, Stephan. On 22 November 2013 13:15, Bruce Griffiths bruce.griffi...@xtra.co.nzwrote: Stephan Sandenbergh wrote: Hi, I'm playing with dual-mixer time difference stuff again. And, came across this and I find it somewhat puzzling since no one else seems to have encountered it. Possibly because I'm missing something? The doubly balanced mixers (of the type known to be used in DMTDs and phase noise measurement systems) are known to have DC offsets. So much so that the guys doing phase noise measurements employ elaborate DC removal circuits in their preamps to combat this. Here's my question: why isn't this DC offset removed in any DMTD circuits I've seen? It seems standard practice to attach the filtered mixer output directly to the zero crossing detector. I did a quick simulation (see attached): The mixer beat is a 10Hz sine 0.7Vpp. If you then use a Collins style zero crossing detector the first stage will have a small gain (I chose a gain of 2.83 from Bruce Griffiths pages ( http://www.ko4bb.com/~bruce/ZeroCrossingDetectors.html)). I then compare this ideal signal to that of a similar one that is offset by 40mV. Notice the asymmetry in the signal due to offset. 40mV result in 1.8ms offset 4mV result in 180us offset Obviously, once the time offset is there no amount of subsequent slope amplification will remove it. I've tested this in practice and bingo, I now have a very accurate way of plotting relative mixer DC offset over time. Any comments? ___ 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. One can always add AC coupling to eliminate this effect as in http://www.wriley.com/A%20Small%20DMTD%20System.pdf Bruce ___ 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 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] DMTD: Mixer DC offset will result in time offset at zero-crossing detector out?
Stephan Sandenbergh wrote: Hi, Thanks - mystery solved. This is one of the systems that I looked at, and missed the DC block in the second amplification stage. I guess it is possibly a large Ceramic 10uF. My bad. Thank you for putting up those web pages I find them to be very good references. I spent quite a lot of time reading through them. Something that puzzles me though is your mixer termination ( http://www.ko4bb.com/~bruce/LowNoiseMixerPreamp.html). What is the logic in having the second balun (and connected in that way)? 1st section is common mode low pass filter, 2nd section is differential common mode low pass filter. Bruce Regards, Stephan. On 22 November 2013 13:15, Bruce Griffithsbruce.griffi...@xtra.co.nzwrote: Stephan Sandenbergh wrote: Hi, I'm playing with dual-mixer time difference stuff again. And, came across this and I find it somewhat puzzling since no one else seems to have encountered it. Possibly because I'm missing something? The doubly balanced mixers (of the type known to be used in DMTDs and phase noise measurement systems) are known to have DC offsets. So much so that the guys doing phase noise measurements employ elaborate DC removal circuits in their preamps to combat this. Here's my question: why isn't this DC offset removed in any DMTD circuits I've seen? It seems standard practice to attach the filtered mixer output directly to the zero crossing detector. I did a quick simulation (see attached): The mixer beat is a 10Hz sine 0.7Vpp. If you then use a Collins style zero crossing detector the first stage will have a small gain (I chose a gain of 2.83 from Bruce Griffiths pages ( http://www.ko4bb.com/~bruce/ZeroCrossingDetectors.html)). I then compare this ideal signal to that of a similar one that is offset by 40mV. Notice the asymmetry in the signal due to offset. 40mV result in 1.8ms offset 4mV result in 180us offset Obviously, once the time offset is there no amount of subsequent slope amplification will remove it. I've tested this in practice and bingo, I now have a very accurate way of plotting relative mixer DC offset over time. Any comments? ___ 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. One can always add AC coupling to eliminate this effect as in http://www.wriley.com/A%20Small%20DMTD%20System.pdf Bruce ___ 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 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 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] DMTD: Mixer DC offset will result in time offset at zero-crossing detector out?
Stephan Did you also notice that the AC coupling is done **after** the sine wave has already been clipped by the previous stage (according to the schematic note)? This generally is not a good way to remove DC offset from a low level 'noisy' signal. I doubt that Bruce was recommending doing it that way. ws - Original Message - From: Stephan Sandenbergh ssandenbe...@gmail.com To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Friday, November 22, 2013 4:19 AM Subject: Re: [time-nuts] DMTD: Mixer DC offset will result in time offset at zero-crossing detector out? Hi, Thanks - mystery solved. This is one of the systems that I looked at, and missed the DC block in the second amplification stage. I guess it is possibly a large Ceramic 10uF. My bad. Thank you for putting up those web pages I find them to be very good references. I spent quite a lot of time reading through them. Something that puzzles me though is your mixer termination ( http://www.ko4bb.com/~bruce/LowNoiseMixerPreamp.html). What is the logic in having the second balun (and connected in that way)? Regards, Stephan. On 22 November 2013 13:15, Bruce Griffiths bruce.griffi...@xtra.co.nzwrote: Stephan Sandenbergh wrote: Hi, I'm playing with dual-mixer time difference stuff again. And, came across this and I find it somewhat puzzling since no one else seems to have encountered it. Possibly because I'm missing something? The doubly balanced mixers (of the type known to be used in DMTDs and phase noise measurement systems) are known to have DC offsets. So much so that the guys doing phase noise measurements employ elaborate DC removal circuits in their preamps to combat this. Here's my question: why isn't this DC offset removed in any DMTD circuits I've seen? It seems standard practice to attach the filtered mixer output directly to the zero crossing detector. I did a quick simulation (see attached): The mixer beat is a 10Hz sine 0.7Vpp. If you then use a Collins style zero crossing detector the first stage will have a small gain (I chose a gain of 2.83 from Bruce Griffiths pages ( http://www.ko4bb.com/~bruce/ZeroCrossingDetectors.html)). I then compare this ideal signal to that of a similar one that is offset by 40mV. Notice the asymmetry in the signal due to offset. 40mV result in 1.8ms offset 4mV result in 180us offset Obviously, once the time offset is there no amount of subsequent slope amplification will remove it. I've tested this in practice and bingo, I now have a very accurate way of plotting relative mixer DC offset over time. Any comments? ___ 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. One can always add AC coupling to eliminate this effect as in http://www.wriley.com/A%20Small%20DMTD%20System.pdf Bruce ___ 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 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] DMTD: Mixer DC offset will result in time offset at zero-crossing detector out?
WarrenS wrote: Stephan Did you also notice that the AC coupling is done **after** the sine wave has already been clipped by the previous stage (according to the schematic note)? This generally is not a good way to remove DC offset from a low level 'noisy' signal. I doubt that Bruce was recommending doing it that way. ws Yes AC coupling after limiting isnt such a good idea. AC coupling either between the mixer and the input stage of the limiter chain or after the last linear stage would be better. Bruce - Original Message - From: Stephan Sandenbergh ssandenbe...@gmail.com To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Friday, November 22, 2013 4:19 AM Subject: Re: [time-nuts] DMTD: Mixer DC offset will result in time offset at zero-crossing detector out? Hi, Thanks - mystery solved. This is one of the systems that I looked at, and missed the DC block in the second amplification stage. I guess it is possibly a large Ceramic 10uF. My bad. Thank you for putting up those web pages I find them to be very good references. I spent quite a lot of time reading through them. Something that puzzles me though is your mixer termination ( http://www.ko4bb.com/~bruce/LowNoiseMixerPreamp.html). What is the logic in having the second balun (and connected in that way)? Regards, Stephan. On 22 November 2013 13:15, Bruce Griffiths bruce.griffi...@xtra.co.nzwrote: Stephan Sandenbergh wrote: Hi, I'm playing with dual-mixer time difference stuff again. And, came across this and I find it somewhat puzzling since no one else seems to have encountered it. Possibly because I'm missing something? The doubly balanced mixers (of the type known to be used in DMTDs and phase noise measurement systems) are known to have DC offsets. So much so that the guys doing phase noise measurements employ elaborate DC removal circuits in their preamps to combat this. Here's my question: why isn't this DC offset removed in any DMTD circuits I've seen? It seems standard practice to attach the filtered mixer output directly to the zero crossing detector. I did a quick simulation (see attached): The mixer beat is a 10Hz sine 0.7Vpp. If you then use a Collins style zero crossing detector the first stage will have a small gain (I chose a gain of 2.83 from Bruce Griffiths pages ( http://www.ko4bb.com/~bruce/ZeroCrossingDetectors.html)). I then compare this ideal signal to that of a similar one that is offset by 40mV. Notice the asymmetry in the signal due to offset. 40mV result in 1.8ms offset 4mV result in 180us offset Obviously, once the time offset is there no amount of subsequent slope amplification will remove it. I've tested this in practice and bingo, I now have a very accurate way of plotting relative mixer DC offset over time. Any comments? ___ 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. One can always add AC coupling to eliminate this effect as in http://www.wriley.com/A%20Small%20DMTD%20System.pdf Bruce ___ 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 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 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.
