Re: [time-nuts] PRS-10 PPS output
iers of more than +/- 1.2us >> (the >>> scope display at 200ns/div), or that the PRS-10 did not create a PPS? >>> >>> Test 2. >>> >>> Trigger on PRS-10 PPS-out and set up the scope delay to 1s, to observe >> the >>> next PPS after the trigger. Set up a mask test. >>> This also indicates a failure. >>> >>> My goal was to get a good low noise and accurate reference oscillator. I >>> bought the PRS-10 for 550 euro, and probably should have just purchased a >>> new one, but live and learn... >>> It probably does not need to be GPS disciplined, but I wanted to get it >>> calibrated before setting it to free-running. >>> >>> At this point, to get further, I probably need a time interval counter, >>> which I can set up using my 4ch 14 bit 500MSPS A/D boards pulse >> stretching >>> input, which should give 5ps RMS time stamping. Unfortunately, right >> now I >>> only have one "good" quality timebase, the PRS-10. I do have an old >>> TrueTime XL-AK GPSDO, but the 10MHz out is noisy, with strong 100Hz spurs >>> (2X line freq in Germany), and my boards on-board 50Mhz tcxo. >>> >>> The two time bases I neglected to mention, are the 10M ref out from my >>> Rigol DG4062, and the 10M ref out from my Siglent SSA 3021X. I cannot >>> comment on their respective quality. >>> >>> Possible test config 1 >>> prs-10 10MHz -> ref in -> LMX2581 (creates 500MHz sample clk for AD9684 >> 14 >>> bit 500MSPS A/D) >>> PRS-10 pps out -> pulse stretcher -> ch0 500MSPS A/D >>> ublox pps out -> ch1 500MSPS ( does not require pulse stretcher, as the >>> leading edge is 48ns, and should interpolate to sub 50ps easily) >>> >>> possible test config 2 >>> 50MHz tcxo -> LMX2581 (creates 500MHz sample clk for AD9684 14 bit >> 500MSPS >>> A/D) >>> PRS-10 pps out -> pulse stretcher -> ch0 500MSPS A/D >>> ublox pps out -> ch1 500MSPS ( does not require pulse stretcher, as the >>> leading edge is 48ns, and should interpolate to sub 50ps easily) >>> PRS-10 10MHz -> ch2 500MSPS >>> >>> I think that test config 2 is probably the best until I can get a good >> free >>> running 10MHz reference. >>> With the shown setup I can store the arrival time/ rising edge zero >>> crossing of all of the inputs to a file for analysis. >>> >>> Any further suggestions on test setup? >>> >>> --mike >>> >>> >>> >>> >>> [image: pps_fail.png] >>> >>> >>> >>> On Sun, Apr 5, 2020 at 6:43 PM Joseph Gwinn >> wrote: >>> >>>> On Sun, 05 Apr 2020 12:00:02 -0400, time-nuts-requ...@lists.febo.com >>>> wrote: >>>> Re: time-nuts Digest, Vol 189, Issue 9 >>>> [snip] >>>>> -- >>>>> >>>>> Message: 2 >>>>> Date: Sat, 4 Apr 2020 14:08:02 -0400 >>>>> From: Bob kb8tq >>>>> To: Discussion of precise time and frequency measurement >>>>> >>>>> Subject: Re: [time-nuts] PRS-10 PPS output >>>>> Message-ID: <1131af5e-3444-4e48-b5d9-ecb36457d...@n1k.org> >>>>> Content-Type: text/plain; charset=utf-8 >>>>> >>>>> Hi >>>>> >>>>> Pulling the output of a normal CMOS gate to ground through a small >>>>> resistor is not generally a good idea. That?s what an attenuator or far >>>>> end termination of the coax is doing. It?s not specifically outlawed in >>>> the >>>>> spec, but it's still not what they are designed to do. Also the output >>>> level >>>>> is going to be pretty wimpy run through an attenuator. >>>>> >>>>> One way to 'fix' the problem is with a 50 ohm series resistor at the >>>> source >>>>> end. That only works to the degree that the output impedance of the >> gate >>>>> is very low when in saturation. How true this is?. that depends. >>>> >>>> Well, the coax 1PPS outputs I've had to deal with are all claim in >>>> their datasheets to be able to drive a 50-ohm load, so I didn't worry >>>> about overloading the output circuitry with a standard attenuator. >>>> Their source impedance seemed to be closer to 200
Re: [time-nuts] PRS-10 PPS output
; Possible test config 1 > > prs-10 10MHz -> ref in -> LMX2581 (creates 500MHz sample clk for AD9684 > 14 > > bit 500MSPS A/D) > > PRS-10 pps out -> pulse stretcher -> ch0 500MSPS A/D > > ublox pps out -> ch1 500MSPS ( does not require pulse stretcher, as the > > leading edge is 48ns, and should interpolate to sub 50ps easily) > > > > possible test config 2 > > 50MHz tcxo -> LMX2581 (creates 500MHz sample clk for AD9684 14 bit > 500MSPS > > A/D) > > PRS-10 pps out -> pulse stretcher -> ch0 500MSPS A/D > > ublox pps out -> ch1 500MSPS ( does not require pulse stretcher, as the > > leading edge is 48ns, and should interpolate to sub 50ps easily) > > PRS-10 10MHz -> ch2 500MSPS > > > > I think that test config 2 is probably the best until I can get a good > free > > running 10MHz reference. > > With the shown setup I can store the arrival time/ rising edge zero > > crossing of all of the inputs to a file for analysis. > > > > Any further suggestions on test setup? > > > > --mike > > > > > > > > > > [image: pps_fail.png] > > > > > > > > On Sun, Apr 5, 2020 at 6:43 PM Joseph Gwinn > wrote: > > > >> On Sun, 05 Apr 2020 12:00:02 -0400, time-nuts-requ...@lists.febo.com > >> wrote: > >> Re: time-nuts Digest, Vol 189, Issue 9 > >> [snip] > >>> -- > >>> > >>> Message: 2 > >>> Date: Sat, 4 Apr 2020 14:08:02 -0400 > >>> From: Bob kb8tq > >>> To: Discussion of precise time and frequency measurement > >>> > >>> Subject: Re: [time-nuts] PRS-10 PPS output > >>> Message-ID: <1131af5e-3444-4e48-b5d9-ecb36457d...@n1k.org> > >>> Content-Type: text/plain; charset=utf-8 > >>> > >>> Hi > >>> > >>> Pulling the output of a normal CMOS gate to ground through a small > >>> resistor is not generally a good idea. That?s what an attenuator or far > >>> end termination of the coax is doing. It?s not specifically outlawed in > >> the > >>> spec, but it's still not what they are designed to do. Also the output > >> level > >>> is going to be pretty wimpy run through an attenuator. > >>> > >>> One way to 'fix' the problem is with a 50 ohm series resistor at the > >> source > >>> end. That only works to the degree that the output impedance of the > gate > >>> is very low when in saturation. How true this is?. that depends. > >> > >> Well, the coax 1PPS outputs I've had to deal with are all claim in > >> their datasheets to be able to drive a 50-ohm load, so I didn't worry > >> about overloading the output circuitry with a standard attenuator. > >> Their source impedance seemed to be closer to 200 ohms, as I recall. > >> > >> The PRS-10 datasheet (page 59) says: "The LOCK/1PPS function may be > >> configured via RS-232. The factory default is a low level to indicate > >> lock, with a 10μs pulse to +5V at 1PPS, with the leading edge being > >> defined as the 1PPS timing reference. This BNC output is a CMOS logic > >> output via a 1kΩ resistor." > >> > >> So, a 50-ohm load (or even a dead short) should not hurt anything. And > >> we can predict the peak voltage over a 50-ohm load driving a 50-ohm > >> coax is 5(25/1000)= 0.125 Vpeak. > >> > >> For the TTL outputs in the days of yore, the series 50-ohm resistor was > >> standard practice. > >> > >> Joe Gwinn > >> > >> > >> Context: > >>> > >>>> I've [JMG] had this issue with coax 1PPS outputs across the board. > >>>> What I generally do is to attach a coaxial 50-ohm attenuator between > >>>> instrument coax output connector and the 50-ohm cable it will drive. > >>>> The attenuator matches the output impedance to the coax impedance. I > >>>> use attenuators between 3 dB and 10 db. The actual attenuation is not > >>>> as marked, because of the mismatch between the ~1K output impedance > and > >>>> the 50-ohm input of the attenuator. I suppose that a 75-ohm > attenuator > >>>> may work as well or better to drive 50-ohm cable, but have not tried > >>>> it. All the ringing et al are suppressed because the length of the > >>>> mismatched part of the path is maybe an inch or two. > >>>> > >> > >> ___ > >> time-nuts mailing list -- time-nuts@lists.febo.com > >> To unsubscribe, go to > >> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > >> and follow the instructions there. > >> > > ___ > > time-nuts mailing list -- time-nuts@lists.febo.com > > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > > and follow the instructions there. > > > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] PRS-10 PPS output
Hi Backing up a little bit …. the PPS in on these telecom Rb’s is designed to easily get the part set on frequency. It’s not designed for a GPSDO application. What you are seeing is consistent with that “application target”. Bob > On Apr 7, 2020, at 6:32 AM, Mike Ingle wrote: > > Hi all, > > Thank you for your feedback. I found the schematics for the PRS-10 online, > and the output is 5V HCMOS. > > signal : > > locked --> hc08 inhc08 out --> hc14 in hc14 out --> 4x 240 ohm > resistors -> output pin > PPS--> hc08 in > > Which brings me to my next question. I have been running this used PRS-10 > FW version 3.21 with apparently (from lady heather) 126000 hours lifetime. > Since Friday when it came in the mail. It has the bench heat sinks and the > accessory output board. It is being disciplined by a blox5T PPS signal. > Occasionally the PPS is missing from the PRS-10 (1 in 1000 or so) . I > presume due to loss of lock, as the and gate would inhibit PPS when lock is > zero. > > First some over-all results, then some background on my testing methodology. > > The PRS-10 seems to lock to PPS-in such that the PRS-10 PPS out is 1.84us > after PPS in. The +1.84us happens to be where the time tag (TT) goes to > zero. I suspect that something might be wrong with the Time Tag setup. > The unit steers itself until the TT=0ns, at which point the TT no longer > returns data. The PPS out from this point seems to wander by about 60ns or > so (delay from GPS PPS in to PPS out). > > Why do I think that I am missing PPS from the PRS-10? > > Test 1. > > GPS PPS -> scope ch2 (1M input on BNC T) -> PRS-10 PPS in > PRS-10 PPS out -> scope ch4 > > scope setup to trigger on ch2 PPS in and look 1.84us (200 ns/div) later at > the PRS-10 PPS out. On infinite persistence, one clearly sees that some > PPS out times remain at ground. > > OK so is the problem that the GPS had outliers of more than +/- 1.2us (the > scope display at 200ns/div), or that the PRS-10 did not create a PPS? > > Test 2. > > Trigger on PRS-10 PPS-out and set up the scope delay to 1s, to observe the > next PPS after the trigger. Set up a mask test. > This also indicates a failure. > > My goal was to get a good low noise and accurate reference oscillator. I > bought the PRS-10 for 550 euro, and probably should have just purchased a > new one, but live and learn... > It probably does not need to be GPS disciplined, but I wanted to get it > calibrated before setting it to free-running. > > At this point, to get further, I probably need a time interval counter, > which I can set up using my 4ch 14 bit 500MSPS A/D boards pulse stretching > input, which should give 5ps RMS time stamping. Unfortunately, right now I > only have one "good" quality timebase, the PRS-10. I do have an old > TrueTime XL-AK GPSDO, but the 10MHz out is noisy, with strong 100Hz spurs > (2X line freq in Germany), and my boards on-board 50Mhz tcxo. > > The two time bases I neglected to mention, are the 10M ref out from my > Rigol DG4062, and the 10M ref out from my Siglent SSA 3021X. I cannot > comment on their respective quality. > > Possible test config 1 > prs-10 10MHz -> ref in -> LMX2581 (creates 500MHz sample clk for AD9684 14 > bit 500MSPS A/D) > PRS-10 pps out -> pulse stretcher -> ch0 500MSPS A/D > ublox pps out -> ch1 500MSPS ( does not require pulse stretcher, as the > leading edge is 48ns, and should interpolate to sub 50ps easily) > > possible test config 2 > 50MHz tcxo -> LMX2581 (creates 500MHz sample clk for AD9684 14 bit 500MSPS > A/D) > PRS-10 pps out -> pulse stretcher -> ch0 500MSPS A/D > ublox pps out -> ch1 500MSPS ( does not require pulse stretcher, as the > leading edge is 48ns, and should interpolate to sub 50ps easily) > PRS-10 10MHz -> ch2 500MSPS > > I think that test config 2 is probably the best until I can get a good free > running 10MHz reference. > With the shown setup I can store the arrival time/ rising edge zero > crossing of all of the inputs to a file for analysis. > > Any further suggestions on test setup? > > --mike > > > > > [image: pps_fail.png] > > > > On Sun, Apr 5, 2020 at 6:43 PM Joseph Gwinn wrote: > >> On Sun, 05 Apr 2020 12:00:02 -0400, time-nuts-requ...@lists.febo.com >> wrote: >> Re: time-nuts Digest, Vol 189, Issue 9 >> [snip] >>> -- >>> >>> Message: 2 >>> Date: Sat, 4 Apr 2020 14:08:02 -0400 >>> From: Bob kb8tq >>> To: Discussion of precise time and frequency measureme
Re: [time-nuts] PRS-10 PPS output
Hi all, Thank you for your feedback. I found the schematics for the PRS-10 online, and the output is 5V HCMOS. signal : locked --> hc08 inhc08 out --> hc14 in hc14 out --> 4x 240 ohm resistors -> output pin PPS--> hc08 in Which brings me to my next question. I have been running this used PRS-10 FW version 3.21 with apparently (from lady heather) 126000 hours lifetime. Since Friday when it came in the mail. It has the bench heat sinks and the accessory output board. It is being disciplined by a blox5T PPS signal. Occasionally the PPS is missing from the PRS-10 (1 in 1000 or so) . I presume due to loss of lock, as the and gate would inhibit PPS when lock is zero. First some over-all results, then some background on my testing methodology. The PRS-10 seems to lock to PPS-in such that the PRS-10 PPS out is 1.84us after PPS in. The +1.84us happens to be where the time tag (TT) goes to zero. I suspect that something might be wrong with the Time Tag setup. The unit steers itself until the TT=0ns, at which point the TT no longer returns data. The PPS out from this point seems to wander by about 60ns or so (delay from GPS PPS in to PPS out). Why do I think that I am missing PPS from the PRS-10? Test 1. GPS PPS -> scope ch2 (1M input on BNC T) -> PRS-10 PPS in PRS-10 PPS out -> scope ch4 scope setup to trigger on ch2 PPS in and look 1.84us (200 ns/div) later at the PRS-10 PPS out. On infinite persistence, one clearly sees that some PPS out times remain at ground. OK so is the problem that the GPS had outliers of more than +/- 1.2us (the scope display at 200ns/div), or that the PRS-10 did not create a PPS? Test 2. Trigger on PRS-10 PPS-out and set up the scope delay to 1s, to observe the next PPS after the trigger. Set up a mask test. This also indicates a failure. My goal was to get a good low noise and accurate reference oscillator. I bought the PRS-10 for 550 euro, and probably should have just purchased a new one, but live and learn... It probably does not need to be GPS disciplined, but I wanted to get it calibrated before setting it to free-running. At this point, to get further, I probably need a time interval counter, which I can set up using my 4ch 14 bit 500MSPS A/D boards pulse stretching input, which should give 5ps RMS time stamping. Unfortunately, right now I only have one "good" quality timebase, the PRS-10. I do have an old TrueTime XL-AK GPSDO, but the 10MHz out is noisy, with strong 100Hz spurs (2X line freq in Germany), and my boards on-board 50Mhz tcxo. The two time bases I neglected to mention, are the 10M ref out from my Rigol DG4062, and the 10M ref out from my Siglent SSA 3021X. I cannot comment on their respective quality. Possible test config 1 prs-10 10MHz -> ref in -> LMX2581 (creates 500MHz sample clk for AD9684 14 bit 500MSPS A/D) PRS-10 pps out -> pulse stretcher -> ch0 500MSPS A/D ublox pps out -> ch1 500MSPS ( does not require pulse stretcher, as the leading edge is 48ns, and should interpolate to sub 50ps easily) possible test config 2 50MHz tcxo -> LMX2581 (creates 500MHz sample clk for AD9684 14 bit 500MSPS A/D) PRS-10 pps out -> pulse stretcher -> ch0 500MSPS A/D ublox pps out -> ch1 500MSPS ( does not require pulse stretcher, as the leading edge is 48ns, and should interpolate to sub 50ps easily) PRS-10 10MHz -> ch2 500MSPS I think that test config 2 is probably the best until I can get a good free running 10MHz reference. With the shown setup I can store the arrival time/ rising edge zero crossing of all of the inputs to a file for analysis. Any further suggestions on test setup? --mike [image: pps_fail.png] On Sun, Apr 5, 2020 at 6:43 PM Joseph Gwinn wrote: > On Sun, 05 Apr 2020 12:00:02 -0400, time-nuts-requ...@lists.febo.com > wrote: > Re: time-nuts Digest, Vol 189, Issue 9 > [snip] > > -- > > > > Message: 2 > > Date: Sat, 4 Apr 2020 14:08:02 -0400 > > From: Bob kb8tq > > To: Discussion of precise time and frequency measurement > > > > Subject: Re: [time-nuts] PRS-10 PPS output > > Message-ID: <1131af5e-3444-4e48-b5d9-ecb36457d...@n1k.org> > > Content-Type: text/plain; charset=utf-8 > > > > Hi > > > > Pulling the output of a normal CMOS gate to ground through a small > > resistor is not generally a good idea. That?s what an attenuator or far > > end termination of the coax is doing. It?s not specifically outlawed in > the > > spec, but it's still not what they are designed to do. Also the output > level > > is going to be pretty wimpy run through an attenuator. > > > > One way to 'fix' the problem is with a 50 ohm series resistor at the > source > > end. That only works to the degree that the output impedance of the
Re: [time-nuts] PRS-10 PPS output
On Sun, 05 Apr 2020 12:00:02 -0400, time-nuts-requ...@lists.febo.com wrote: Re: time-nuts Digest, Vol 189, Issue 9 [snip] > -- > > Message: 2 > Date: Sat, 4 Apr 2020 14:08:02 -0400 > From: Bob kb8tq > To: Discussion of precise time and frequency measurement > > Subject: Re: [time-nuts] PRS-10 PPS output > Message-ID: <1131af5e-3444-4e48-b5d9-ecb36457d...@n1k.org> > Content-Type: text/plain; charset=utf-8 > > Hi > > Pulling the output of a normal CMOS gate to ground through a small > resistor is not generally a good idea. That?s what an attenuator or far > end termination of the coax is doing. It?s not specifically outlawed in the > spec, but it's still not what they are designed to do. Also the output level > is going to be pretty wimpy run through an attenuator. > > One way to 'fix' the problem is with a 50 ohm series resistor at the source > end. That only works to the degree that the output impedance of the gate > is very low when in saturation. How true this is?. that depends. Well, the coax 1PPS outputs I've had to deal with are all claim in their datasheets to be able to drive a 50-ohm load, so I didn't worry about overloading the output circuitry with a standard attenuator. Their source impedance seemed to be closer to 200 ohms, as I recall. The PRS-10 datasheet (page 59) says: "The LOCK/1PPS function may be configured via RS-232. The factory default is a low level to indicate lock, with a 10μs pulse to +5V at 1PPS, with the leading edge being defined as the 1PPS timing reference. This BNC output is a CMOS logic output via a 1kΩ resistor." So, a 50-ohm load (or even a dead short) should not hurt anything. And we can predict the peak voltage over a 50-ohm load driving a 50-ohm coax is 5(25/1000)= 0.125 Vpeak. For the TTL outputs in the days of yore, the series 50-ohm resistor was standard practice. Joe Gwinn Context: > >> I've [JMG] had this issue with coax 1PPS outputs across the board. >> What I generally do is to attach a coaxial 50-ohm attenuator between >> instrument coax output connector and the 50-ohm cable it will drive. >> The attenuator matches the output impedance to the coax impedance. I >> use attenuators between 3 dB and 10 db. The actual attenuation is not >> as marked, because of the mismatch between the ~1K output impedance and >> the 50-ohm input of the attenuator. I suppose that a 75-ohm attenuator >> may work as well or better to drive 50-ohm cable, but have not tried >> it. All the ringing et al are suppressed because the length of the >> mismatched part of the path is maybe an inch or two. >> ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] PRS-10 PPS output
Hi Pulling the output of a normal CMOS gate to ground through a small resistor is not generally a good idea. That’s what an attenuator or far end termination of the coax is doing. It’s not specifically outlawed in the spec, but it’s still not what they are designed to do. Also the output level is going to be pretty wimpy run through an attenuator. One way to “fix” the problem is with a 50 ohm series resistor at the source end. That only works to the degree that the output impedance of the gate is very low when in saturation. How true this is …. that depends. A far better approach is to buffer the output through something like a set of 2, 3, or 4 NC7SZ125’s (or similar) in parallel. The output from something like that has much higher drive capability than a single gate output. Source termination with a single 50 ohm or with 100, 150, or 200 ohms on each gate works pretty well in this case. (If you want to dig further into the details of “why source termination?” there are several posts from Said back about 4 or 5 years ago). You do have the problem of not knowing what the “far end” is expecting. If it has a 50 ohm load *and* is looking for a 5V logic signal …. source termination isn’t going to work with normal logic gates doing the drive end of things. You would need a high speed gate that is happy with a 10V supply to do that ….. Unfortunately, there *is* gear out there that terminates a PPS with a 50 ohm load *and* expects some sort of logic level. Is it set up for 1.2V, 1.65V, 2.5V …. Often this is not very well documented. If you *do* set up to “straight drive” a 50 ohm end termination to 5V in order to do right by a 2.5V logic level: Spend some time looking at the power distribution approach on your board. That’s a 0.1A 10 us wide pulse you are thumping onto the supply rail….. Bob > On Apr 4, 2020, at 1:20 PM, Joseph Gwinn wrote: > > On Fri, 03 Apr 2020 20:00:59 -0400, time-nuts-requ...@lists.febo.com > wrote: > > Re: time-nuts Digest, Vol 189, Issue 7 > - >> >> Message: 1 >> Date: Fri, 3 Apr 2020 15:48:50 -0400 >> From: Bob kb8tq >> To: Discussion of precise time and frequency measurement >> >> Subject: Re: [time-nuts] PRS-10 PPS output >> >> Hi >> >> At least according to page 20 in: >> >> https://www.thinksrs.com/downloads/pdfs/manuals/PRS10m.pdf >> >> the ?raw? PPS output from the PRS-10 is just a CMOS gate output. >> There is nothing suggesting it is designed to drive a 50 ohm load >> or a coax cable. >> > [snip] >> >> Best guess: It's doing what it's supposed to, but not quite what >> you expected it to do. >> >> >> Message: 2 >> Date: Fri, 3 Apr 2020 20:27:25 + (UTC) >> From: Taka Kamiya >> To: Discussion of precise time and frequency measurement >> >> Subject: Re: [time-nuts] PRS-10 PPS output >> >> I've seen this with my own.? You are catching the leading edge of >> ringing of the signal.? >> >> Since the output is CMOS, and high impedance, it really doesn't have >> enough current to push through low impedance cables.? Try shorter and >> different cable.? Terminate it with 50 ohms.? Set the trigger level >> little higher.? In my setup, the cable is actually a very short >> twisted pair, and only 2" long into a buffer board. > > I've had this issue with coax 1PPS outputs across the board. What I > generally do is to attach a coaxial 50-ohm attenuator between > instrument coax output connector and the 50-ohm cable it will drive. > The attenuator matches the output impedance to the coax impedance. I > use attenuators between 3 dB and 10 db. The actual attenuation is not > as marked, because of the mismatch between the ~1K output impedance and > the 50-ohm input of the attenuator. I suppose that a 75-ohm attenuator > may work as well or better to drive 50-ohm cable, but have not tried > it. All the ringing et al are suppressed because the length of the > mismatched part of the path is maybe an inch or two. > > Joe Gwinn > >> >> End of time-nuts Digest, Vol 189, Issue 7 >> * > > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] PRS-10 PPS output
On Fri, 03 Apr 2020 20:00:59 -0400, time-nuts-requ...@lists.febo.com wrote: Re: time-nuts Digest, Vol 189, Issue 7 - > > Message: 1 > Date: Fri, 3 Apr 2020 15:48:50 -0400 > From: Bob kb8tq > To: Discussion of precise time and frequency measurement > > Subject: Re: [time-nuts] PRS-10 PPS output > > Hi > > At least according to page 20 in: > > https://www.thinksrs.com/downloads/pdfs/manuals/PRS10m.pdf > > the ?raw? PPS output from the PRS-10 is just a CMOS gate output. > There is nothing suggesting it is designed to drive a 50 ohm load > or a coax cable. > [snip] > > Best guess: It's doing what it's supposed to, but not quite what > you expected it to do. > > > Message: 2 > Date: Fri, 3 Apr 2020 20:27:25 + (UTC) > From: Taka Kamiya > To: Discussion of precise time and frequency measurement > > Subject: Re: [time-nuts] PRS-10 PPS output > > I've seen this with my own.? You are catching the leading edge of > ringing of the signal.? > > Since the output is CMOS, and high impedance, it really doesn't have > enough current to push through low impedance cables.? Try shorter and > different cable.? Terminate it with 50 ohms.? Set the trigger level > little higher.? In my setup, the cable is actually a very short > twisted pair, and only 2" long into a buffer board. I've had this issue with coax 1PPS outputs across the board. What I generally do is to attach a coaxial 50-ohm attenuator between instrument coax output connector and the 50-ohm cable it will drive. The attenuator matches the output impedance to the coax impedance. I use attenuators between 3 dB and 10 db. The actual attenuation is not as marked, because of the mismatch between the ~1K output impedance and the 50-ohm input of the attenuator. I suppose that a 75-ohm attenuator may work as well or better to drive 50-ohm cable, but have not tried it. All the ringing et al are suppressed because the length of the mismatched part of the path is maybe an inch or two. Joe Gwinn > > End of time-nuts Digest, Vol 189, Issue 7 > * ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] PRS-10 PPS output
I've seen this with my own. You are catching the leading edge of ringing of the signal. Since the output is CMOS, and high impedance, it really doesn't have enough current to push through low impedance cables. Try shorter and different cable. Terminate it with 50 ohms. Set the trigger level little higher. In my setup, the cable is actually a very short twisted pair, and only 2" long into a buffer board. You might want to look at what your PRS-10 is set to, as far as pulse width is concerned. Also, use much longer horizontal scan rate. The standard pulse width is 10 MICRO second. Your image is capturing beginning of the pulse but not the whole of it. --- (Mr.) Taka Kamiya KB4EMF / ex JF2DKG On Friday, April 3, 2020, 3:21:09 PM EDT, Mike Ingle wrote: Hello fellow nuts, I just received my PRS-10 with boardlet and heat sink, and I have a question regarding my PPS output signal. My output looks strange, (but usable). I have attached a couple screen-shots of my scope/ The first is with 50 ohm termination after 5foot of 5g-58 cable, the second is without termination. --mike [image: pps_term.png] [image: pps_unterm.png] ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
