Re: [time-nuts] T.I. experimenting - newbie question
You cannot change impedance without changing geometry or dielectric, and any of these changes will affect vop. Didier KO4BB Sent from my BlackBerry Wireless thingy while I do other things... -Original Message- From: Joseph Gray jg...@zianet.com Sender: time-nuts-boun...@febo.com Date: Sun, 3 Apr 2011 16:37:05 To: Discussion of precise time and frequency measurementtime-nuts@febo.com Reply-To: Discussion of precise time and frequency measurement time-nuts@febo.com Subject: Re: [time-nuts] T.I. experimenting - newbie question I assume you mean that impedance has an effect on VOP? Can you point to any internet sources that explain this effect? Preferably something not overly technical. Joe Gray W5JG On Sun, Apr 3, 2011 at 4:11 PM, paul swed paulsw...@gmail.com wrote: It does change vop ___ 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] T.I. experimenting - newbie question
Hal, Here are the results I got using your suggestion. The numbers may be a bit different than last night as I'm not sure I'm using the same cable. A+, B+ = 18.9 ns A-, B- = 19.4 ns Obviously there is some difference in delay between the A and B channels. Otherwise, the two numbers would have been identical - correct? If I take the average of the two readings, I get 19.05 ns, which is more precise than the readings I'm taking. I'm rounding to the nearest 0.1 ns on the readings. A+, B- = 5014.6 ns A-, B+ = 5023.5 ns If I take the average of these two readings and subtract out the 5 us for 1/2 period of the 100 KHz square wave, if get 19.15 ns. This agrees very closely with the above average. I haven't looked at the service manual for the 5328A yet, so I don't know if I even have the proper equipment to attempt a calibration. In the mean time, would you say that taking the average of the first two readings is a valid method? Joe Gray W5JG On Sun, Apr 3, 2011 at 7:18 PM, Hal Murray hmur...@megapathdsl.net wrote: How about a square wave? Start on one edge, stop on the next cycle. You can play with start on rising edge, stop on falling and the reverse. They should add up to the total. ___ 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] T.I. experimenting - newbie question
I'm keeping the newbie question in the subject for those who wish to ignore this thread. To those who respond, your contribution to the diminution of my ignorance is appreciated :-) I had borrowed two different 5328A counters. I just compared them, using the exact same coax, connectors and settings. Both units were warmed up for over one hour. In my previous readings, I was averaging for 1 s and rounding to one decimal place. The following readings are averaged for 10 s and rounded to two decimal places. This seemed like a good place to round, as the readings were stable enough to this point. Old 5328A (slide power switch): + + = 19.43 ns - - = 19.49 ns Newer 5328A (toggle power switch): + + = 18.92 ns - - = 19.41 ns The A and B inputs on the old unit match much more closely. If I average the readings of each unit, there is more than 200 ps difference between the old and new unit. How do I know which one is correct? Joe Gray W5JG On Mon, Apr 4, 2011 at 8:25 PM, Joseph Gray jg...@zianet.com wrote: Hal, Here are the results I got using your suggestion. The numbers may be a bit different than last night as I'm not sure I'm using the same cable. A+, B+ = 18.9 ns A-, B- = 19.4 ns Obviously there is some difference in delay between the A and B channels. Otherwise, the two numbers would have been identical - correct? If I take the average of the two readings, I get 19.05 ns, which is more precise than the readings I'm taking. I'm rounding to the nearest 0.1 ns on the readings. A+, B- = 5014.6 ns A-, B+ = 5023.5 ns If I take the average of these two readings and subtract out the 5 us for 1/2 period of the 100 KHz square wave, if get 19.15 ns. This agrees very closely with the above average. I haven't looked at the service manual for the 5328A yet, so I don't know if I even have the proper equipment to attempt a calibration. In the mean time, would you say that taking the average of the first two readings is a valid method? Joe Gray W5JG On Sun, Apr 3, 2011 at 7:18 PM, Hal Murray hmur...@megapathdsl.net wrote: How about a square wave? Start on one edge, stop on the next cycle. You can play with start on rising edge, stop on falling and the reverse. They should add up to the total. ___ 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] T.I. experimenting - newbie question
Does the counter have setable input threasholds? Most do. Are they set the the same? -John I'm keeping the newbie question in the subject for those who wish to ignore this thread. To those who respond, your contribution to the diminution of my ignorance is appreciated :-) I had borrowed two different 5328A counters. I just compared them, using the exact same coax, connectors and settings. Both units were warmed up for over one hour. In my previous readings, I was averaging for 1 s and rounding to one decimal place. The following readings are averaged for 10 s and rounded to two decimal places. This seemed like a good place to round, as the readings were stable enough to this point. Old 5328A (slide power switch): + + = 19.43 ns - - = 19.49 ns Newer 5328A (toggle power switch): + + = 18.92 ns - - = 19.41 ns The A and B inputs on the old unit match much more closely. If I average the readings of each unit, there is more than 200 ps difference between the old and new unit. How do I know which one is correct? Joe Gray W5JG On Mon, Apr 4, 2011 at 8:25 PM, Joseph Gray jg...@zianet.com wrote: Hal, Here are the results I got using your suggestion. The numbers may be a bit different than last night as I'm not sure I'm using the same cable. A+, B+ = 18.9 ns A-, B- = 19.4 ns Obviously there is some difference in delay between the A and B channels. Otherwise, the two numbers would have been identical - correct? If I take the average of the two readings, I get 19.05 ns, which is more precise than the readings I'm taking. I'm rounding to the nearest 0.1 ns on the readings. A+, B- = 5014.6 ns A-, B+ = 5023.5 ns If I take the average of these two readings and subtract out the 5 us for 1/2 period of the 100 KHz square wave, if get 19.15 ns. This agrees very closely with the above average. I haven't looked at the service manual for the 5328A yet, so I don't know if I even have the proper equipment to attempt a calibration. In the mean time, would you say that taking the average of the first two readings is a valid method? Joe Gray W5JG On Sun, Apr 3, 2011 at 7:18 PM, Hal Murray hmur...@megapathdsl.net wrote: How about a square wave? Start on one edge, stop on the next cycle. You can play with start on rising edge, stop on falling and the reverse. They should add up to the total. ___ 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] T.I. experimenting - newbie question
Here are the results I got using your suggestion. The numbers may be a bit different than last night as I'm not sure I'm using the same cable. A+, B+ = 18.9 ns A-, B- = 19.4 ns Obviously there is some difference in delay between the A and B channels. Otherwise, the two numbers would have been identical - correct? ... If I take the average of the two readings, I get 19.05 ns, which is more precise than the readings I'm taking. I'm rounding to the nearest 0.1 ns on the readings. There are several possibilities for asymmetry. The input signal could have other than a 50/50 high/low ratio. The trigger levels could be set at other than the half-way point. Do you have a scope? There are probably second order problems with different rise/fall times. A+, B- = 5014.6 ns A-, B+ = 5023.5 ns If I take the average of these two readings and subtract out the 5 us for 1/2 period of the 100 KHz square wave, if get 19.15 ns. This agrees very closely with the above average. I read that as everything mostly works. The question is how well does it work and/or what can you do to get more/better data? You can get another set of numbers by swapping the A and B inputs so the signal goes from B to A rather than A to B. Some of the errors might be more obvious if you deliberately offset the trigger levels. NB: That's for all 4 modes: A+ to B+ will be slightly less than a whole cycle. A+ to B- will be slightly less than a 1/2 cycle. ... -- These are my opinions, not necessarily my employer's. 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.
Re: [time-nuts] T.I. experimenting - newbie question
John, Yes, they both do. However, only one has the DVM option that lets me measure the voltage trigger levels. When I turned off preset and set the levels manually to match, I got similar numbers to using preset. On Mon, Apr 4, 2011 at 10:13 PM, J. Forster j...@quik.com wrote: Does the counter have setable input threasholds? Most do. Are they set the the same? -John ___ 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] T.I. experimenting - newbie question
Hal, replies inline. On Mon, Apr 4, 2011 at 10:21 PM, Hal Murray hmur...@megapathdsl.net wrote: Here are the results I got using your suggestion. The numbers may be a bit different than last night as I'm not sure I'm using the same cable. A+, B+ = 18.9 ns A-, B- = 19.4 ns Obviously there is some difference in delay between the A and B channels. Otherwise, the two numbers would have been identical - correct? ... If I take the average of the two readings, I get 19.05 ns, which is more precise than the readings I'm taking. I'm rounding to the nearest 0.1 ns on the readings. There are several possibilities for asymmetry. The input signal could have other than a 50/50 high/low ratio. The trigger levels could be set at other than the half-way point. See my reply to John about trigger levels. Do you have a scope? Yes, I will dig out the scope and check. The last time I checked the Spectracom 8140 (long ago), it was ok. I'll check it again. There are probably second order problems with different rise/fall times. A+, B- = 5014.6 ns A-, B+ = 5023.5 ns If I take the average of these two readings and subtract out the 5 us for 1/2 period of the 100 KHz square wave, if get 19.15 ns. This agrees very closely with the above average. I read that as everything mostly works. That was my assumption, but it's nice to have someone more knowledgeable confirm it. The question is how well does it work and/or what can you do to get more/better data? You can get another set of numbers by swapping the A and B inputs so the signal goes from B to A rather than A to B. Some of the errors might be more obvious if you deliberately offset the trigger levels. NB: That's for all 4 modes: A+ to B+ will be slightly less than a whole cycle. A+ to B- will be slightly less than a 1/2 cycle. I'll try swapping inputs and see what happens. I'm not sure if I'll get to this tonight. If not, tomorrow night. Joe Gray W5JG ___ 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] T.I. experimenting - newbie question
Another interesting measurement would be to use the timebase output and external reference to compare the readings using the same timebase. Or are you already using a gpsdo? On Apr 5, 2011, at 12:08 AM, Joseph Gray jg...@zianet.com wrote: I'm keeping the newbie question in the subject for those who wish to ignore this thread. To those who respond, your contribution to the diminution of my ignorance is appreciated :-) I had borrowed two different 5328A counters. I just compared them, using the exact same coax, connectors and settings. Both units were warmed up for over one hour. In my previous readings, I was averaging for 1 s and rounding to one decimal place. The following readings are averaged for 10 s and rounded to two decimal places. This seemed like a good place to round, as the readings were stable enough to this point. Old 5328A (slide power switch): + + = 19.43 ns - - = 19.49 ns Newer 5328A (toggle power switch): + + = 18.92 ns - - = 19.41 ns The A and B inputs on the old unit match much more closely. If I average the readings of each unit, there is more than 200 ps difference between the old and new unit. How do I know which one is correct? Joe Gray W5JG On Mon, Apr 4, 2011 at 8:25 PM, Joseph Gray jg...@zianet.com wrote: Hal, Here are the results I got using your suggestion. The numbers may be a bit different than last night as I'm not sure I'm using the same cable. A+, B+ = 18.9 ns A-, B- = 19.4 ns Obviously there is some difference in delay between the A and B channels. Otherwise, the two numbers would have been identical - correct? If I take the average of the two readings, I get 19.05 ns, which is more precise than the readings I'm taking. I'm rounding to the nearest 0.1 ns on the readings. A+, B- = 5014.6 ns A-, B+ = 5023.5 ns If I take the average of these two readings and subtract out the 5 us for 1/2 period of the 100 KHz square wave, if get 19.15 ns. This agrees very closely with the above average. I haven't looked at the service manual for the 5328A yet, so I don't know if I even have the proper equipment to attempt a calibration. In the mean time, would you say that taking the average of the first two readings is a valid method? Joe Gray W5JG On Sun, Apr 3, 2011 at 7:18 PM, Hal Murray hmur...@megapathdsl.net wrote: How about a square wave? Start on one edge, stop on the next cycle. You can play with start on rising edge, stop on falling and the reverse. They should add up to the total. ___ 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] T.I. experimenting - newbie question
If I understand you correctly, then I did not have things setup symetrically. Now I have a tee on each of the A and B inputs. The unused port on the B tee has a 50 Ohm terminator. Is this what you mean? Symmetry makes it easier to see what is going on. If you use a Tee on the B input, then the timing from the center of the Tee on the A input to the internal logic should match the same setup on the B port. That lets you focus on what is between the two Tees. With the above setup, using the shortest cable I have gives me 1.5 ns. Adding the longer cable to the shorter, using a F-F BNC coupler gives me 21 ns, for a difference of 19.5 ns. Adding the barrel complicates things. What is the delay through the barrel? (My guess would be about an inch at 50% of c, so that's ballpark of 0.2 ns.) If you swap the short cable for a longer one, then the only difference is the change in length. -- These are my opinions, not necessarily my employer's. 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.
Re: [time-nuts] T.I. experimenting - newbie question
On 04/03/2011 12:40 PM, Hal Murray wrote: If I understand you correctly, then I did not have things setup symetrically. Now I have a tee on each of the A and B inputs. The unused port on the B tee has a 50 Ohm terminator. Is this what you mean? Symmetry makes it easier to see what is going on. If you use a Tee on the B input, then the timing from the center of the Tee on the A input to the internal logic should match the same setup on the B port. That lets you focus on what is between the two Tees. Trouble is that you have added the electrical length of a tee inbetween the center-to-center distance. You still need to calibrate that out of the equation. Still not much, but it's a bias. Consider that you have three cables (tc1, tc2, tc3), a barrel (tb) and input offset (toff). You measure them t1 = toff + tc1 t2 = toff + tc2 t3 = toff + tc3 t4 = toff + tc1 + tb + tc2 t5 = toff + tc1 + tb + tc3 t6 = toff + tc2 + tb + tc3 6 measurements for 5 unknowns should work out well. Remove one cable and you only make 3 measurements for 4 unknowns. With the above setup, using the shortest cable I have gives me 1.5 ns. Adding the longer cable to the shorter, using a F-F BNC coupler gives me 21 ns, for a difference of 19.5 ns. Adding the barrel complicates things. What is the delay through the barrel? (My guess would be about an inch at 50% of c, so that's ballpark of 0.2 ns.) If you swap the short cable for a longer one, then the only difference is the change in length. Only helps for diffrence in delay, not actual delay. Cheers, Magnus ___ 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] T.I. experimenting - newbie question
At 09:42 PM 4/2/2011, Joseph Gray wrote... I'm reading 18.9 ns. The coax specs give a VOP of 66%. This should calculate out to a length of 3.74 M. When I measure the coax, I get 3.8 M. Your calculation is incorrect. If the velocity factor only has 2 significant digits, the result of the calculation can only have 2 significant digits. And, I doubt the coax manufacturer will guarantee the VF to 1 part in 66. VF is the reciprocal of the square root of the dielectric constant of the coax insulator. 66% implies you're using a cable which uses solid polyethylene. A quick google for the dielectric constant of polyethylene shows a range (2.2-2.4 depending on the source). That would be a VF range of .67-.65. Working your numbers, I get a length of 3.7-3.8 m. ___ 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] T.I. experimenting - newbie question
Thanks again to everyone who replied. I obviously have much more to learn about this topic. I will do some reading and more experimenting. The comments so far have put me on the right track. Joe Gray W5JG ___ 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] T.I. experimenting - newbie question
With any decent TDR you can SEE all the connections so you can measure the cable length (+/- a few mm) directly. Regards, David Partridge -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Magnus Danielson Sent: 03 April 2011 12:46 To: time-nuts@febo.com Subject: Re: [time-nuts] T.I. experimenting - newbie question On 04/03/2011 12:40 PM, Hal Murray wrote: If I understand you correctly, then I did not have things setup symetrically. Now I have a tee on each of the A and B inputs. The unused port on the B tee has a 50 Ohm terminator. Is this what you mean? Symmetry makes it easier to see what is going on. If you use a Tee on the B input, then the timing from the center of the Tee on the A input to the internal logic should match the same setup on the B port. That lets you focus on what is between the two Tees. Trouble is that you have added the electrical length of a tee inbetween the center-to-center distance. You still need to calibrate that out of the equation. Still not much, but it's a bias. Consider that you have three cables (tc1, tc2, tc3), a barrel (tb) and input offset (toff). You measure them t1 = toff + tc1 t2 = toff + tc2 t3 = toff + tc3 t4 = toff + tc1 + tb + tc2 t5 = toff + tc1 + tb + tc3 t6 = toff + tc2 + tb + tc3 6 measurements for 5 unknowns should work out well. Remove one cable and you only make 3 measurements for 4 unknowns. With the above setup, using the shortest cable I have gives me 1.5 ns. Adding the longer cable to the shorter, using a F-F BNC coupler gives me 21 ns, for a difference of 19.5 ns. Adding the barrel complicates things. What is the delay through the barrel? (My guess would be about an inch at 50% of c, so that's ballpark of 0.2 ns.) If you swap the short cable for a longer one, then the only difference is the change in length. Only helps for diffrence in delay, not actual delay. Cheers, Magnus ___ 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] T.I. experimenting - newbie question
On 04/03/2011 09:33 PM, David C. Partridge wrote: With any decent TDR you can SEE all the connections so you can measure the cable length (+/- a few mm) directly. No, you can't. You can measure the electrical length. I do have a decent TDR at hand. You would have to assume the speed in the cable to know the physical length. It's not a high-quality measure mostly. Cheers, Magnus ___ 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] T.I. experimenting - newbie question
For extra points, test with the same long cable at different temperatures. Say from soaking in a 150 deg F oven and a zero degree freezer. Bill Hawkins ___ 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] T.I. experimenting - newbie question
That's an interesting question. Does temperature have an effect on the dielectric that changes the VOP? I'll have to try your experiment. Is that worth ten extra credit points? :-) The copper in the coax has a positive temperature coefficient, which will contribute to an increased impedance (assuming the reactive components don't change). But, does the impedance have any effect on VOP? A quick Google search didn't find any information on this. AFAIK VOP is due to the dielectric properties. Joe Gray W5JG On Sun, Apr 3, 2011 at 3:21 PM, Bill Hawkins b...@iaxs.net wrote: For extra points, test with the same long cable at different temperatures. Say from soaking in a 150 deg F oven and a zero degree freezer. Bill Hawkins ___ 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] T.I. experimenting - newbie question
It does change vop On Sun, Apr 3, 2011 at 5:52 PM, Joseph Gray jg...@zianet.com wrote: That's an interesting question. Does temperature have an effect on the dielectric that changes the VOP? I'll have to try your experiment. Is that worth ten extra credit points? :-) The copper in the coax has a positive temperature coefficient, which will contribute to an increased impedance (assuming the reactive components don't change). But, does the impedance have any effect on VOP? A quick Google search didn't find any information on this. AFAIK VOP is due to the dielectric properties. Joe Gray W5JG On Sun, Apr 3, 2011 at 3:21 PM, Bill Hawkins b...@iaxs.net wrote: For extra points, test with the same long cable at different temperatures. Say from soaking in a 150 deg F oven and a zero degree freezer. Bill Hawkins ___ 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] T.I. experimenting - newbie question
On 04/03/2011 11:52 PM, Joseph Gray wrote: That's an interesting question. Does temperature have an effect on the dielectric that changes the VOP? I'll have to try your experiment. Is that worth ten extra credit points? :-) The copper in the coax has a positive temperature coefficient, which will contribute to an increased impedance (assuming the reactive components don't change). But, does the impedance have any effect on VOP? A quick Google search didn't find any information on this. AFAIK VOP is due to the dielectric properties. Yes, and the dielectric properties change with temperature and hence will the speed of the signals. Blow bubbles in the dielectric and the speed goes up and dependence of temperature goes down. Same thing happens with fibre. As I recall it about 1/10 of the shift was due to becoming longer from heat and the rest from the dielectric. Cheers, Magnus ___ 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] T.I. experimenting - newbie question
I assume you mean that impedance has an effect on VOP? Can you point to any internet sources that explain this effect? Preferably something not overly technical. Joe Gray W5JG On Sun, Apr 3, 2011 at 4:11 PM, paul swed paulsw...@gmail.com wrote: It does change vop ___ 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] T.I. experimenting - newbie question
Hi Joe, Both VoP and impedance depend on relative permittivity (dielectric constant). See the section Derived Electrical Parameters on Wikipedia. http://en.wikipedia.org/wiki/Coaxial_cable Brent On 4/3/2011 4:37 PM, Joseph Gray wrote: I assume you mean that impedance has an effect on VOP? Can you point to any internet sources that explain this effect? Preferably something not overly technical. Joe Gray W5JG On Sun, Apr 3, 2011 at 4:11 PM, paul swedpaulsw...@gmail.com wrote: It does change vop ___ 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] T.I. experimenting - newbie question
But, does the impedance have any effect on VOP? Not normally. It's 1/sqrt(dielectric constant * magnetic permeability) For most materials used as insulators, the magnetic permeability is 1 so we tend to drop that part. http://en.wikipedia.org/wiki/Coaxial_cable There are a couple of interesting cases where you don't have a simple dielectric constant. Outer traces on a PCB have air on one side and glass/plastic on the other side. They are slightly faster than inner traces. That corresponds to a lower dielectric constant which is what you would expect if mixed glass/plastic with air. (Most of the energy is between the trace and the adjacent plane so the air doesn't contribute much.) Foam coax is a mix of plastic and air. That gives a lower dielectric constant and lower loss. (That's lower than solid whatever material you are using.) If you find a chart of coax impedance and pick similar insulation at 50 and 75 ohms, the velocity will be the same. -- These are my opinions, not necessarily my employer's. 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.
Re: [time-nuts] T.I. experimenting - newbie question
Joe, The coax can be viewed as a series of lumped constants; that is, series inductors with many shunt capacitors to ground in between the inductors. In essence, a delay line. At standard temperature / pressure / etc. the delay line assumes a given value. If any external influence impacts the coax then it assumes a new value because of : 1. Capacitive and inductive changes from dimensional shifts OR 2. Changing dielectric properties OR 3. Some combination of the above Thus the delay line's value (VOP) changes, and, naturally the impedance as well. BillWB6BNQ Joseph Gray wrote: I assume you mean that impedance has an effect on VOP? Can you point to any internet sources that explain this effect? Preferably something not overly technical. Joe Gray W5JG On Sun, Apr 3, 2011 at 4:11 PM, paul swed paulsw...@gmail.com wrote: It does change vop ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to [1]https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. References 1. https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts ___ 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] T.I. experimenting - newbie question
Bottom line is that using a chunk of coax (even air line) as a time delay standard is like using a ruler made of a rubber band to check the accuracy of a SS maxchinist's scale. YMMV, -John === Joe, The coax can be viewed as a series of lumped constants; that is, series inductors with many shunt capacitors to ground in between the inductors. In essence, a delay line. At standard temperature / pressure / etc. the delay line assumes a given value. If any external influence impacts the coax then it assumes a new value because of : 1. Capacitive and inductive changes from dimensional shifts OR 2. Changing dielectric properties OR 3. Some combination of the above Thus the delay line's value (VOP) changes, and, naturally the impedance as well. BillWB6BNQ Joseph Gray wrote: I assume you mean that impedance has an effect on VOP? Can you point to any internet sources that explain this effect? Preferably something not overly technical. Joe Gray W5JG On Sun, Apr 3, 2011 at 4:11 PM, paul swed paulsw...@gmail.com wrote: It does change vop ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to [1]https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. References 1. https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts ___ 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] T.I. experimenting - newbie question
John, I wasn't expecting the coax to be a precision standard. However, since you bring it up, can you recommend something that I could use as a precision standard to test a T.I. counter? Preferably something that is inexpensive and easy to make. Joe Gray W5JG On Sun, Apr 3, 2011 at 6:11 PM, J. Forster j...@quik.com wrote: Bottom line is that using a chunk of coax (even air line) as a time delay standard is like using a ruler made of a rubber band to check the accuracy of a SS maxchinist's scale. YMMV, -John ___ 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] T.I. experimenting - newbie question
Air dielectric coax is about the best you can do, AFAIK. -John == John, I wasn't expecting the coax to be a precision standard. However, since you bring it up, can you recommend something that I could use as a precision standard to test a T.I. counter? Preferably something that is inexpensive and easy to make. Joe Gray W5JG On Sun, Apr 3, 2011 at 6:11 PM, J. Forster j...@quik.com wrote: Bottom line is that using a chunk of coax (even air line) as a time delay standard is like using a ruler made of a rubber band to check the accuracy of a SS maxchinist's scale. YMMV, -John ___ 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] T.I. experimenting - newbie question
The electrical length of a piece of coax does change with temp. The Gore catalog, for instance, has a graph of it. And it has a most annoying bump right around 20 to 25 C, at least for the stuff I use at work. As to why... The length changes for one thing. I think, also, there will be a change due to the change in diameter, as well as the density of the dielectric, which will change the capacitance per unit length. On Apr 3, 2011, at 14:52, Joseph Gray jg...@zianet.com wrote: That's an interesting question. Does temperature have an effect on the dielectric that changes the VOP? I'll have to try your experiment. Is that worth ten extra credit points? :-) The copper in the coax has a positive temperature coefficient, which will contribute to an increased impedance (assuming the reactive components don't change). But, does the impedance have any effect on VOP? A quick Google search didn't find any information on this. AFAIK VOP is due to the dielectric properties. Joe Gray W5JG On Sun, Apr 3, 2011 at 3:21 PM, Bill Hawkins b...@iaxs.net wrote: For extra points, test with the same long cable at different temperatures. Say from soaking in a 150 deg F oven and a zero degree freezer. Bill Hawkins ___ 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] T.I. experimenting - newbie question
Joseph Gray wrote: I have a borrowed HP 5328A with the Universal Module. I'm using averaging mode and auto triggering. Counter does not have the OCXO option. I'm using the internal oscillator, not locking to my GPSDO. I was just messing around with a length of Belden 9273 and the 100 KHz square wave output from my Spectracom distribution amp. Start signal is the 100 KHz signal. Using a tee, the stop signal is the same 100 KHz after passing through the length of coax. I'm reading 18.9 ns. The coax specs give a VOP of 66%. This should calculate out to a length of 3.74 M. When I measure the coax, I get 3.8 M. I am including the BNC connectors in my length measurement. If I subtract them, I'm much closer to my calculated length. Should the BNC connector lengths be included or not? Or, is the measurement I'm getting as good as it gets with this HP counter? Joe Gray W5JG The measured delay includes the time offset between the start and stop inputs. This is unlikely to be zero, you need to measure it and subtract the offset from the measured result. Since the 5328A can only measure positive time intervals measuring this offset is somewhat tricky to do. 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] T.I. experimenting - newbie question
Interesting followup. With the exact same setup, but replacing the tee with a Wenzel power divider, I get 18.6 ns. On Sat, Apr 2, 2011 at 7:42 PM, Joseph Gray jg...@zianet.com wrote: I have a borrowed HP 5328A with the Universal Module. I'm using averaging mode and auto triggering. Counter does not have the OCXO option. I'm using the internal oscillator, not locking to my GPSDO. I was just messing around with a length of Belden 9273 and the 100 KHz square wave output from my Spectracom distribution amp. Start signal is the 100 KHz signal. Using a tee, the stop signal is the same 100 KHz after passing through the length of coax. I'm reading 18.9 ns. The coax specs give a VOP of 66%. This should calculate out to a length of 3.74 M. When I measure the coax, I get 3.8 M. I am including the BNC connectors in my length measurement. If I subtract them, I'm much closer to my calculated length. Should the BNC connector lengths be included or not? Or, is the measurement I'm getting as good as it gets with this HP counter? Joe Gray W5JG ___ 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] T.I. experimenting - newbie question
Bruce Griffiths wrote: Joseph Gray wrote: I have a borrowed HP 5328A with the Universal Module. I'm using averaging mode and auto triggering. Counter does not have the OCXO option. I'm using the internal oscillator, not locking to my GPSDO. I was just messing around with a length of Belden 9273 and the 100 KHz square wave output from my Spectracom distribution amp. Start signal is the 100 KHz signal. Using a tee, the stop signal is the same 100 KHz after passing through the length of coax. I'm reading 18.9 ns. The coax specs give a VOP of 66%. This should calculate out to a length of 3.74 M. When I measure the coax, I get 3.8 M. I am including the BNC connectors in my length measurement. If I subtract them, I'm much closer to my calculated length. Should the BNC connector lengths be included or not? Or, is the measurement I'm getting as good as it gets with this HP counter? Joe Gray W5JG The measured delay includes the time offset between the start and stop inputs. This is unlikely to be zero, you need to measure it and subtract the offset from the measured result. Since the 5328A can only measure positive time intervals measuring this offset is somewhat tricky to do. Bruce The simplest way of measuring the cable delay with the 5328A is to measure the delay with a short length of cable between the start and stop inputs and then increase the length of cable by connecting the cable to be measured in series with the first cable measure the delay again and subtract the first measurement from the second. This procedure corrects for the start to stop offset as well as that of the first cable. Then the effects of finite rise time, trigger thresholds and reflections should be considered. One then has to consider the effects of the various connectors, ___ 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] T.I. experimenting - newbie question
Joseph Gray wrote: Interesting followup. With the exact same setup, but replacing the tee with a Wenzel power divider, I get 18.6 ns. Resistive or rf power divider? Using the latter may result in significant reflections. On Sat, Apr 2, 2011 at 7:42 PM, Joseph Grayjg...@zianet.com wrote: I have a borrowed HP 5328A with the Universal Module. I'm using averaging mode and auto triggering. Counter does not have the OCXO option. I'm using the internal oscillator, not locking to my GPSDO. I was just messing around with a length of Belden 9273 and the 100 KHz square wave output from my Spectracom distribution amp. Start signal is the 100 KHz signal. Using a tee, the stop signal is the same 100 KHz after passing through the length of coax. I'm reading 18.9 ns. The coax specs give a VOP of 66%. This should calculate out to a length of 3.74 M. When I measure the coax, I get 3.8 M. I am including the BNC connectors in my length measurement. If I subtract them, I'm much closer to my calculated length. Should the BNC connector lengths be included or not? Or, is the measurement I'm getting as good as it gets with this HP counter? Joe Gray W5JG 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] T.I. experimenting - newbie question
Seems like you are asking where the reference plane of a BNC is. The distance between the reference planes defines the electrical length of a cable or adapter or L or T. Unlike precision connectors like the APC-7 or GR 900, the reference plane of a BNC is not well defined. A quick Google turned up nothing really useful. So, at a guess, if you look at a female BNC, the Teflon surrounding the center conductor is flush with the end of the cut off end of that conductor. This is about 0.0 to 0.2 below the end of the outside conductor. My GUESS is that cut off end is the reference plane. This corresponds to the bottom of the annular well in the male VNC. You might be able to find more info by researching VNAs or TDRs, Remember, a BNC is not a precision connector. Best, -John == I have a borrowed HP 5328A with the Universal Module. I'm using averaging mode and auto triggering. Counter does not have the OCXO option. I'm using the internal oscillator, not locking to my GPSDO. I was just messing around with a length of Belden 9273 and the 100 KHz square wave output from my Spectracom distribution amp. Start signal is the 100 KHz signal. Using a tee, the stop signal is the same 100 KHz after passing through the length of coax. I'm reading 18.9 ns. The coax specs give a VOP of 66%. This should calculate out to a length of 3.74 M. When I measure the coax, I get 3.8 M. I am including the BNC connectors in my length measurement. If I subtract them, I'm much closer to my calculated length. Should the BNC connector lengths be included or not? Or, is the measurement I'm getting as good as it gets with this HP counter? Joe Gray W5JG ___ 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] T.I. experimenting - newbie question
On Sat, Apr 2, 2011 at 8:06 PM, Bruce Griffiths bruce.griffi...@xtra.co.nz wrote: Resistive or rf power divider? Using the latter may result in significant reflections. RF divider. Perhaps I should make a resistive divider. Joe Gray W5JG ___ 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] T.I. experimenting - newbie question
Thanks for the input. I'll try a bit more experimenting and see what I get. As for the measured cable length, do I include the BNC connectors or not? Joe Gray W5JG On Sat, Apr 2, 2011 at 8:03 PM, Bruce Griffiths bruce.griffi...@xtra.co.nz wrote: Bruce Griffiths wrote: The measured delay includes the time offset between the start and stop inputs. This is unlikely to be zero, you need to measure it and subtract the offset from the measured result. Since the 5328A can only measure positive time intervals measuring this offset is somewhat tricky to do. Bruce The simplest way of measuring the cable delay with the 5328A is to measure the delay with a short length of cable between the start and stop inputs and then increase the length of cable by connecting the cable to be measured in series with the first cable measure the delay again and subtract the first measurement from the second. This procedure corrects for the start to stop offset as well as that of the first cable. Then the effects of finite rise time, trigger thresholds and reflections should be considered. One then has to consider the effects of the various connectors, ___ 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] T.I. experimenting - newbie question
As for the measured cable length, do I include the BNC connectors or not? You want the difference in path lengths. Is there an asymmetry in the setup? If so, count the BNC connectors that don't have a match on the other path. If you have input-Tee-coax-Tee-terminator, then the difference is the coax plus half of each Tee. That is you want to measure the length from center of Tee to center of Tee. If you have a splitter, then the length is the difference in coax lengths. (assuming everything else is symmetric) -- These are my opinions, not necessarily my employer's. 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.
Re: [time-nuts] T.I. experimenting - newbie question
I've always been partial to differential measurements. So many things fall out when you do the subtraction. Make short and long cables using the same wire and connectors. Measure the time delay for each. Subtract the short delay from the long delay to get Td. Subtract the length of the short cable from the length of the long cable to get Ld. The delay per unit length of cable is Td/Ld. If the connectors are a significant part of the delay, you can't use Td/(delay/unit length) to find the virtual end of the cable inside the connectors because the unit length delay changes in the connector. Try it with several different lengths of cable. If the unit length delay changes, something else is going on. Bill Hawkins ___ 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] T.I. experimenting - newbie question
Yes, that is a better way of phrasing my question. If you are correct, then that would make about 14 mm difference in my measured length, which would bring me even closer to my calculated length. And the tee may also be adding to my error margin. Time for more experiments :-) Joe Gray W5JG On Sat, Apr 2, 2011 at 8:05 PM, J. Forster j...@quik.com wrote: Seems like you are asking where the reference plane of a BNC is. The distance between the reference planes defines the electrical length of a cable or adapter or L or T. Unlike precision connectors like the APC-7 or GR 900, the reference plane of a BNC is not well defined. A quick Google turned up nothing really useful. So, at a guess, if you look at a female BNC, the Teflon surrounding the center conductor is flush with the end of the cut off end of that conductor. This is about 0.0 to 0.2 below the end of the outside conductor. My GUESS is that cut off end is the reference plane. This corresponds to the bottom of the annular well in the male VNC. ___ 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] T.I. experimenting - newbie question
On 04/03/2011 04:03 AM, Bruce Griffiths wrote: Bruce Griffiths wrote: Joseph Gray wrote: I have a borrowed HP 5328A with the Universal Module. I'm using averaging mode and auto triggering. Counter does not have the OCXO option. I'm using the internal oscillator, not locking to my GPSDO. I was just messing around with a length of Belden 9273 and the 100 KHz square wave output from my Spectracom distribution amp. Start signal is the 100 KHz signal. Using a tee, the stop signal is the same 100 KHz after passing through the length of coax. I'm reading 18.9 ns. The coax specs give a VOP of 66%. This should calculate out to a length of 3.74 M. When I measure the coax, I get 3.8 M. I am including the BNC connectors in my length measurement. If I subtract them, I'm much closer to my calculated length. Should the BNC connector lengths be included or not? Or, is the measurement I'm getting as good as it gets with this HP counter? Joe Gray W5JG The measured delay includes the time offset between the start and stop inputs. This is unlikely to be zero, you need to measure it and subtract the offset from the measured result. Since the 5328A can only measure positive time intervals measuring this offset is somewhat tricky to do. Bruce The simplest way of measuring the cable delay with the 5328A is to measure the delay with a short length of cable between the start and stop inputs and then increase the length of cable by connecting the cable to be measured in series with the first cable measure the delay again and subtract the first measurement from the second. This procedure corrects for the start to stop offset as well as that of the first cable. Then the effects of finite rise time, trigger thresholds and reflections should be considered. One then has to consider the effects of the various connectors, You would also need to consider the delay effect of the BNC sex-converter to hook the two cables up. You can do that by doing the following measurements: Measure the short cable. Measure the short and DUT cable. Measure the DUT cable. t1 = ts t2 = ts + tc + tDUT t3 = tDUT Solving for the connector delay tc is simple. You won't resolve the delay offsets of the measurement itself. Cheers, Magnus ___ 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] T.I. experimenting - newbie question
If I understand you correctly, then I did not have things setup symetrically. Now I have a tee on each of the A and B inputs. The unused port on the B tee has a 50 Ohm terminator. Is this what you mean? With the above setup, using the shortest cable I have gives me 1.5 ns. Adding the longer cable to the shorter, using a F-F BNC coupler gives me 21 ns, for a difference of 19.5 ns. The readings are bouncing around a bit, so these numbers aren't exact. Using the 19.5 ns figure and a 66% VOP, I get 3.86 M, which is much closer to the measured length. If I use the calculated length vs the measured length, I get a VOP = 65%. Pretty close to the specified 66%. Thanks to everyone for the help. Any more hints or discussion are always appreciated. Joe Gray W5JG On Sat, Apr 2, 2011 at 8:55 PM, Hal Murray hmur...@megapathdsl.net wrote: You want the difference in path lengths. Is there an asymmetry in the setup? If so, count the BNC connectors that don't have a match on the other path. If you have input-Tee-coax-Tee-terminator, then the difference is the coax plus half of each Tee. That is you want to measure the length from center of Tee to center of Tee. ___ 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] T.I. experimenting - newbie question
Speaking of the 5328A, for strictly T.I. use, would having the OCXO option be better? I have a different frequency counter that is much better for that purpose. Joe Gray W5JG ___ 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] T.I. experimenting - newbie question
I would not trust the VOP of any coax cable of a non-precision types. Generally, if you need that kind of precision, you use air line or hard line and measure it with a TDR. -John = If I understand you correctly, then I did not have things setup symetrically. Now I have a tee on each of the A and B inputs. The unused port on the B tee has a 50 Ohm terminator. Is this what you mean? With the above setup, using the shortest cable I have gives me 1.5 ns. Adding the longer cable to the shorter, using a F-F BNC coupler gives me 21 ns, for a difference of 19.5 ns. The readings are bouncing around a bit, so these numbers aren't exact. Using the 19.5 ns figure and a 66% VOP, I get 3.86 M, which is much closer to the measured length. If I use the calculated length vs the measured length, I get a VOP = 65%. Pretty close to the specified 66%. Thanks to everyone for the help. Any more hints or discussion are always appreciated. Joe Gray W5JG On Sat, Apr 2, 2011 at 8:55 PM, Hal Murray hmur...@megapathdsl.net wrote: You want the difference in path lengths. Is there an asymmetry in the setup? If so, count the BNC connectors that don't have a match on the other path. If you have input-Tee-coax-Tee-terminator, then the difference is the coax plus half of each Tee. That is you want to measure the length from center of Tee to center of Tee. ___ 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] T.I. experimenting - newbie question
Oops. I just noticed that I had previously punched the wrong button and had the wrong frequency out of the Spectracom. Using the loweset frequency of 100 KHz (as I thought I was using before), the T.I. readings are much more stable. Using these new numbers gets me even closer to the measured cable length. If we're measuring from the center of each tee as suggested, I think I'm dead on. So, I assume that this particular 5328A is performing as it should in T.I. mode. I checked it in frequency mode against my GPSDO and it reads 11 Hz high. In A/B mode, I get the correct ratios. That's probably enough experimenting for tonight. I'll save some fun for tomorrow :-) Joe Gray W5JG ___ 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] T.I. experimenting - newbie question
John, the intent was not to precisely measure the VOP, although I would expect Belden cable to be fairly close. I'm just messing around with a piece of equipment that I haven't used before and doing simple experiments to see if I get reasonable results. I used to own a 5370A, but it had something wrong with it. I never got around to fixing the problem, so I sold it. From what I can tell so far, this 5328A seems to be working ok. Joe Gray W5JG On Sat, Apr 2, 2011 at 10:22 PM, J. Forster j...@quik.com wrote: I would not trust the VOP of any coax cable of a non-precision types. Generally, if you need that kind of precision, you use air line or hard line and measure it with a TDR. -John = ___ 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.
