[time-nuts] How can I measure time-delay of a cable with HP 5370B time-interval counter?

slawdabr@wp.pl slawdabr at wp.pl
Mon Oct 29 18:01:36 EDT 2018


Hello,  Maybe this method will help:   1. connect splitter to generator ,any two coaxes to splitter and then connect them to start and stop channel of TIC (CAB I and CAB II)  2. Generate any time interval (period, pulse width etc)  3. Measured time interval is zero - level, reference level(TI0)  4. Connect coax under test to CAB II and then TIC channel  5. Generate the same time interval as in p.2  6. Measured TI is TI1  7. Replace CAB II and coax under test, generate the same time interval as in p.2  8. Measured TI is TI2  9. Calculate delay: T = TI0 - (TI1+TI2)/2   For best result, use the same timebase for generator and TIC  
                
              
               
                 
                  Dnia 29 października 2018 17:00 time-nuts-request at lists.febo.c napisał(a):
                 
                 
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 Today's Topics: 
  
   1. Re: How can I measure time-delay of a cable with HP 5370B 
      time-interval counter? (David C. Partridge) 
   2. Re: How can I measure time-delay of a cable with HP 5370B 
      time-interval counter? (Artek Manuals) 
   3. Re: Question about noisetypes and ADEV (Attila Kinali) 
   4. Re: Question about noisetypes and ADEV (Magnus Danielson) 
   5. Re: How can I measure time-delay of a cable with HP 5370B 
      time-interval counter? (Chris Caudle) 
   6. Re: How can I measure time-delay of a cable with HP 5370B 
      time-interval counter? (Dr. David Kirkby) 
  
  
 ------------------------------ 
  
 Message: 1 
 Date: Mon, 29 Oct 2018 10:38:52 -0000 
 From: "David C. Partridge" <david.partridge at perdrix.co.uk 
 To: "'Discussion of precise time and frequency measurement'" 
 	<time-nuts at lists.febo.com> 
 Subject: Re: [time-nuts] How can I measure time-delay of a cable with 
 	HP 5370B time-interval counter? 
 Message-ID: <004801d46f73$96e047b0$c4a0d71 
 Content-Type: text/plain;	charset="us-ascii" 
  
 If you have a Tektronix 7000 series 'scope, then a 7S12 equipped with a S52 
 pulse generator and an S6 sampler head will talk all the pain out of 
 measuring cable length and will also show you any impedance mismatches. 
 This way you don't need to suspect a bad cable, you can prove it's bad. 
  
 If you need a cable checked, I can do it as I have 7S12 plugins. 
 Dave 
  
 -----Original Message----- 
 From: time-nuts [mailto:time-nuts-bounces at list On Behalf Of Dr. 
 David Kirkby 
 Sent: 29 October 2018 00:50 
 To:   time-nuts at lists.febo.com 
 Subject: [time-nuts] How can I measure time-delay of a cable with HP 5370B 
 time-interval counter? 
  
 I'm trying to do something which would seem conceptually easy, but I'm 
 getting results I can't understand. I wish to measure the delay (in 
 seconds) of a bit of length of coaxial cable. 
  
 I'm feeding a sine wave from a Stanford Research DS345 30 MHz function 
 generator via a coax to the START input of the counter, then with a BNC 
 T-piece, of 480 mm of 50 ohm cable to the STOP input of the counter. Here's 
 a photo of the complete setup. 
  
 www.kirkbymicrowave.co.uk www.kirkbymicrowave.co.uk 
 enerator-to-start-then-stop.jp 
  
 I've set the 5370B's START impedance to be 1 M ohm, and the STOP to be 50 
 ohms, so the function generator should see a 50 ohm load, as 1 M ohm in 
 parallel with 50 ohms is virtually 50 ohms. 
  
 The switch position on the counter are as shown here 
  
 www.kirkbymicrowave.co.uk www.kirkbymicrowave.co.uk 
 s.jpg 
  
 So the main settings are 
  
 * TI mode. 
 * +/- TI 
 * START. 1 M ohm, positive slope, level to preset position (0 V) 
 * STOP 50 ohm, positive slope, level to preset position (0 V) 
  
 With the cable 480 mm in length, the velocity factor of the cable being 
 approximately 0.7, I would have expected an electrical length of around 686 
 mm, and so a delay of 
  
 time =  distance / velocity = 0.686 / 3e8 
 = 2.29 ns. 
  
 I would not be surprised by small changes in delay with frequency, which is 
 what I wanted to investigate. But I'm getting the following readings, for 
 different frequencies of the function generator 
  
 1 kHz - unstable readings, around 100~300 us. 
 10 kHz  -> -21.3 us 
 50 kHz -> -4.27 us 
 100 kHz -> -1.90 us 
 250 kHz -> - 528 ns 
 500 kHz -> 1.837 us 
 1 MHz -> 956 ns 
 2 MHz -> 490 ns 
 3 MHz -> -2.6 ns 
 4 MHz -> -0.33 ns 
 5 MHz -> 0.90 ns 
 6 MHz -> 1.50 ns 
 7 MHz -> 1.93 ns 
 8 MHz -> 2.15 ns 
 9 MHz -> 2.38 ns 
 10 MHz -> 2.52 ns 
 11 MHz -> 2.60 ns 
 20 MHz -> 2.85 ns 
 30 MHz -> 2.80 ns 
  
 The numbers look believable  with a frequency input of 10 MHz or more. I 
 did not do the complete set again, but using a cable of 1.53 m in length, 
 where I would expect the delay to be around 7.29 ns, the results were 
  
 1 MHz  -> -26.51 ns 
 5 MHz -> 9.70 ns 
 10 MHz -> 9.70 ns 
 15 MHz -> -57.81 ns 
 20 MHz -> -41.64 ns 
 30 MHz -> 7.13 ns 
  
 Note, the function generator and counter do not share a common frequency 
 standard for this test. I have not tried it with them locked to the same 10 
 MHz reference, but I somewhat doubt that is the cause of these issues. 
  
 I must be missing something, but I'm not sure what it is. 
  
 --  
 Dr David Kirkby Ph.D C.Eng MIET 
 Kirkby Microwave Ltd 
 Registered office: Stokes Hall Lodge, Burnham Rd, Althorne, CHELMSFORD, 
 Essex, CM3 6DT, United Kingdom. 
 Registered in England and Wales as company number 08914892 
 www.kirkbymicrowave.co.uk www.kirkbymicrowave.co.uk 
 Tel 01621-680100 / +44 1621-680100 
 ______________________________ 
 time-nuts mailing list --   time-nuts at lists.febo.com 
 To unsubscribe, go to 
 lists.febo.com lists.febo.com 
 and follow the instructions there. 
  
  
  
  
 ------------------------------ 
  
 Message: 2 
 Date: Mon, 29 Oct 2018 07:57:00 -0400 
 From: Artek Manuals <Manuals at ArtekManuals.com> 
 To:   time-nuts at lists.febo.com 
 Subject: Re: [time-nuts] How can I measure time-delay of a cable with 
 	HP 5370B time-interval counter? 
 Message-ID: <b0ac7b03-c460-7e6d-1d5d-163fd 
 Content-Type: text/plain; charset=windows-1252; format=flowed 
  
 David 
  
 First let me say that I have never used a 5370B 
  
 Ignoring the lower frequency stuff for the moment, Can you measure (  
 accurately) the trigger levels of both the start and stop gates? Slight  
 differences in the trigger points at each end will will obviously add  
 error in the measurement. 
  
 The next flag for thought is your comment "assuming a velocity factor of  
 .7" What if the velocity factor is really .66 ? This would account for  
 almost half of the error. 
  
 Rerun you data with larger and smaller output levels from the function  
 generator. Increasing error" with lower signal levels (or vice versa  
 lower erros with increased voltage ) would implicate a trigger  
 differences as the source of error as well 
  
 Dave 
  manuals at artekmanuals.com 
  
 David on another note I tried replying to you directly and the email  
 bounced ? 
  
 On 10/29/2018 6:38 AM, David C. Partridge wrote: 
  
 <SNIP> 
 
 If 
  
 I'm trying to do something which would seem conceptually easy, but I'm 
 getting results I can't understand. I wish to measure the delay (in 
 seconds) of a bit of length of coaxial cable. 
  
 I'm feeding a sine wave from a Stanford Research DS345 30 MHz function 
 generator via a coax to the START input of the counter, then with a BNC 
 T-piece, of 480 mm of 50 ohm cable to the STOP input of the counter. Here's 
 a photo of the complete setup. 
  
 www.kirkbymicrowave.co.uk www.kirkbymicrowave.co.uk 
 enerator-to-start-then-stop.jp 
  
 I've set the 5370B's START impedance to be 1 M ohm, and the STOP to be 50 
 ohms, so the function generator should see a 50 ohm load, as 1 M ohm in 
 parallel with 50 ohms is virtually 50 ohms. 
  
 The switch position on the counter are as shown here 
  
 www.kirkbymicrowave.co.uk www.kirkbymicrowave.co.uk 
 s.jpg 
  
 So the main settings are 
  
 * TI mode. 
 * +/- TI 
 * START. 1 M ohm, positive slope, level to preset position (0 V) 
 * STOP 50 ohm, positive slope, level to preset position (0 V) 
  
 With the cable 480 mm in length, the velocity factor of the cable being 
 approximately 0.7, I would have expected an electrical length of around 686 
 mm, and so a delay of 
  
 time =  distance / velocity = 0.686 / 3e8 
 = 2.29 ns. 
  
 I would not be surprised by small changes in delay with frequency, which is 
 what I wanted to investigate. But I'm getting the following readings, for 
 different frequencies of the function generator 
  
 1 kHz - unstable readings, around 100~300 us. 
 10 kHz  -> -21.3 us 
 50 kHz -> -4.27 us 
 100 kHz -> -1.90 us 
 250 kHz -> - 528 ns 
 500 kHz -> 1.837 us 
 1 MHz -> 956 ns 
 2 MHz -> 490 ns 
 3 MHz -> -2.6 ns 
 4 MHz -> -0.33 ns 
 5 MHz -> 0.90 ns 
 6 MHz -> 1.50 ns 
 7 MHz -> 1.93 ns 
 8 MHz -> 2.15 ns 
 9 MHz -> 2.38 ns 
 10 MHz -> 2.52 ns 
 11 MHz -> 2.60 ns 
 20 MHz -> 2.85 ns 
 30 MHz -> 2.80 ns 
  
 The numbers look believable  with a frequency input of 10 MHz or more. I 
 did not do the complete set again, but using a cable of 1.53 m in length, 
 where I would expect the delay to be around 7.29 ns, the results were 
  
 1 MHz  -> -26.51 ns 
 5 MHz -> 9.70 ns 
 10 MHz -> 9.70 ns 
 15 MHz -> -57.81 ns 
 20 MHz -> -41.64 ns 
 30 MHz -> 7.13 ns 
  
 Note, the function generator and counter do not share a common frequency 
 standard for this test. I have not tried it with them locked to the same 10 
 MHz reference, but I somewhat doubt that is the cause of these issues. 
  
 I must be missing something, but I'm not sure what it is. 
  
 
  
 --  
 Dave 
  Manuals at ArtekManuals.com 
 www.ArtekManuals.com 
  
  
 --- 
 This email has been checked for viruses by Avast antivirus software. 
 www.avast.com www.avast.com 
  
  
  
  
 ------------------------------ 
  
 Message: 3 
 Date: Mon, 29 Oct 2018 14:59:08 +0100 
 From: Attila Kinali <attila at kinali.ch> 
 To: Discussion of precise time and frequency measurement 
 	<time-nuts at lists.febo.com> 
 Subject: Re: [time-nuts] Question about noisetypes and ADEV 
 Message-ID: <20181029145908.f7fde144af2bc1 
 Content-Type: text/plain; charset=ISO-8859-1 
  
 Moin, 
  
 I'm bunching a few mails together, to not clutter the mailinglist too much 
  
 On Sat, 27 Oct 2018 23:25:30 +0200 
 Magnus Danielson <magnus at rubidium.dyndns.org> wrote: 
  
 
 The integration is very important aspect, as a number of assumptions 
 becomes embedded into it, such as the f_H frequency which is the Nyquist 
 frequency for counters, so sampling interval is also a relevant 
 parameter for expected level. 
 
  
 An important thing to note here is that Gaussian white noise is, 
 as it is defined, non-continuous (by any continuity measure). 
 Ie if you take two samples, no matter how close they are time-wise, 
 their difference in value can be arbitrary large. If you are integrating 
 over (time-continuous) Gaussian white noise, you have to argue 
 carefully, why this integral is defined (meaning why calculating it 
 leads to a single, well defined value). In our case, it's usually 
 enough to assume that there is a finite cut-off frequency at which 
 point the signal falls off with at least 1/f^2 (or >=40dB/dec) to 
 ensure 1) continuity and 2) convergence of the integral. 
  
 For more details, see a textbook on Ito-calculus, e.g. [1] 
  
 On Sat, 27 Oct 2018 23:43:33 +0200 
 Magnus Danielson <magnus at rubidium.dyndns.org> wrote: 
  
 
 A simple trick to transform uniform distribution to normal distribution 
 like shape is to take 12 samples and add them together. A special trick 
 is to take them pair-wise and subtract them and then add 6 differences, 
 to avoid DC bias of typical uniform distribution generation (as typical 
 pseudo-noise generators does not have all 0 state in them). The result 
 of this subtract-add trick is a normal distribution like thing with the 
 standard distribution of 1. More or fewer sample-pairs can be added if 
 the product is scaled appropriately. 
  
 The Box-Mueller algorithm is another way to convert uniform distribution 
 to normal distribution. 
 
  
 Please, plase, please, do not use "just 12 samples and add them together" 
 as an approach for generating normal distributed values! Even if it will 
 get you something that looks like a normal distribution, it's quite far 
 from it. It is also a very slow method and uses up a lot of randomnes. 
  
 Box-M?ller is a usable alternative, though I would recommend using 
 the Ziggurat Method[2], which is very fast and leads to a very good 
 approximation. When I replaced the "take 30 samples and add them" of 
 Fran?ois Vernotte's Sigmatheta package[3] and used the Ziggurat Method, 
 combined with xorshift1024*[4] for random number generation, I got 
 a total speed up of a factor of more than 2 (including the FFT and 
 everything)[5] (yes, I know that xorshift1024* does have some problems 
 in the quality of random numbers generated, but they shouldn't be 
 relevant for the application at hand). 
  
  
 			Attila Kinali 
  
 [1] "Stochastic Differential Equations", by Bernt ?ksendal, 2013 (6th ed) 
  
 [2] "The Ziggurat Method for Generating Random Variables",  
 by Marsaglia and Tsang, 2000 
 dx.doi.org dx.doi.org 
  
 [3]  theta.obs-besancon.fr theta.obs-besancon.fr 
  
 [4]  xoshiro.di.unimi.it xoshiro.di.unimi.it   
 or more specifically:  xoroshiro.di.unimi.it xoroshiro.di.unimi.it 
  
 [5]  git.kinali.ch git.kinali.ch 
 --  
 It is upon moral qualities that a society is ultimately founded. All  
 the prosperity and technological sophistication in the world is of no  
 use without that foundation. 
                  Miss Matheson, The Diamond Age, Neal Stephenson 
  
  
  
 ------------------------------ 
  
 Message: 4 
 Date: Mon, 29 Oct 2018 15:28:28 +0100 
 From: Magnus Danielson <magnus at rubidium.dyndns.org> 
 To:   time-nuts at lists.febo.com 
 Cc:   magnus at rubidium.se 
 Subject: Re: [time-nuts] Question about noisetypes and ADEV 
 Message-ID: <2abfba15-f9f7-2ff6-bff8-0ec46 
 Content-Type: text/plain; charset=utf-8 
  
 Hi Attila, 
  
 On 10/29/18 2:59 PM, Attila Kinali wrote: 
 
 Moin, 
  
 I'm bunching a few mails together, to not clutter the mailinglist too much 
  
 On Sat, 27 Oct 2018 23:25:30 +0200 
 Magnus Danielson <magnus at rubidium.dyndns.org> wrote: 
  
 
 The integration is very important aspect, as a number of assumptions 
 becomes embedded into it, such as the f_H frequency which is the Nyquist 
 frequency for counters, so sampling interval is also a relevant 
 parameter for expected level. 
 
  
 An important thing to note here is that Gaussian white noise is, 
 as it is defined, non-continuous (by any continuity measure). 
 Ie if you take two samples, no matter how close they are time-wise, 
 their difference in value can be arbitrary large. If you are integrating 
 over (time-continuous) Gaussian white noise, you have to argue 
 carefully, why this integral is defined (meaning why calculating it 
 leads to a single, well defined value). In our case, it's usually 
 enough to assume that there is a finite cut-off frequency at which 
 point the signal falls off with at least 1/f^2 (or >=40dB/dec) to 
 ensure 1) continuity and 2) convergence of the integral. 
 
  
 There is aspects of noise which is more or less important depending on 
 what you do. As we leave WPM it is no longer gaussian anyway. For ADEV 
 and friends the shape of the PDF isn't as important as for other things. 
 The slope of the frequency range is however the important one. It is 
 only when we do the confidence intervals where the Gaussian shape 
 becomes relevant for the Chi-square bounds, but those are usually not 
 precise enough that even rough Gaussian shape is relevant. Even for 
 noises with none-Gaussian properties, the Chi-square seems to be valid 
 enough. 
  
 For other measures, like bit-error simulations, proper Gaussian shape is 
 much more important, but only to a certain point. For higher BER values, 
 the details of the outer part of the shape isn't all that important, 
 it's only as you push into lower BER numbers you need to care. 
  
 
 For more details, see a textbook on Ito-calculus, e.g. [1] 
  
 On Sat, 27 Oct 2018 23:43:33 +0200 
 Magnus Danielson <magnus at rubidium.dyndns.org> wrote: 
  
 
 A simple trick to transform uniform distribution to normal distribution 
 like shape is to take 12 samples and add them together. A special trick 
 is to take them pair-wise and subtract them and then add 6 differences, 
 to avoid DC bias of typical uniform distribution generation (as typical 
 pseudo-noise generators does not have all 0 state in them). The result 
 of this subtract-add trick is a normal distribution like thing with the 
 standard distribution of 1. More or fewer sample-pairs can be added if 
 the product is scaled appropriately. 
  
 The Box-Mueller algorithm is another way to convert uniform distribution 
 to normal distribution. 
 
  
 Please, plase, please, do not use "just 12 samples and add them together" 
 as an approach for generating normal distributed values! Even if it will 
 get you something that looks like a normal distribution, it's quite far 
 from it. It is also a very slow method and uses up a lot of randomnes. 
 
  
 Actually, for many simulations you do not need better "shape". 
 There is some simulations where shape comes in, but others where it has 
 little to no consequence. 
  
 
 Box-M?ller is a usable alternative, though I would recommend using 
 the Ziggurat Method[2], which is very fast and leads to a very good 
 approximation. When I replaced the "take 30 samples and add them" of 
 Fran?ois Vernotte's Sigmatheta package[3] and used the Ziggurat Method, 
 combined with xorshift1024*[4] for random number generation, I got 
 a total speed up of a factor of more than 2 (including the FFT and 
 everything)[5] (yes, I know that xorshift1024* does have some problems 
 in the quality of random numbers generated, but they shouldn't be 
 relevant for the application at hand). 
 
  
 Getting suitable PRNG polynomials isn't all that hard, if the length of 
 the "random" sequence is of concern compared to the length of the 
 sequence used. It's a solved problem. 
  
 Never the less, thanks for the many references. Will read up on them 
 eventually. 
  
 Cheers, 
 Magnus 
  
 
  
 			Attila Kinali 
  
 [1] "Stochastic Differential Equations", by Bernt ?ksendal, 2013 (6th ed) 
  
 [2] "The Ziggurat Method for Generating Random Variables",  
 by Marsaglia and Tsang, 2000 
 dx.doi.org dx.doi.org 
  
 [3]  theta.obs-besancon.fr theta.obs-besancon.fr 
  
 [4]  xoshiro.di.unimi.it xoshiro.di.unimi.it   
 or more specifically:  xoroshiro.di.unimi.it xoroshiro.di.unimi.it 
  
 [5]  git.kinali.ch git.kinali.ch 
  
 
  
  
  
 ------------------------------ 
  
 Message: 5 
 Date: Mon, 29 Oct 2018 10:01:32 -0500 
 From: "Chris Caudle" <chris at chriscaudle.org> 
 To:   time-nuts at lists.febo.com 
 Subject: Re: [time-nuts] How can I measure time-delay of a cable with 
 	HP 5370B time-interval counter? 
 Message-ID: 
 	<4c942efd15520e6d47bdb068bf3b 
 Content-Type: text/plain;charset=iso-8859-1 
  
 On Mon, October 29, 2018 6:57 am, Artek Manuals wrote: 
 
 The next flag for thought is your comment "assuming a velocity factor of 
 .7" What if the velocity factor is really .66 ? This would account for 
 almost half of the error. 
 
  
 Propagation velocity has an inverse dependence on permittivity, and 
 permittivity changes with frequency.  Electrical delay time will not be 
 constant with frequency because of that. 
  
 In addition to the fundamental physics at play, there are instrumentation 
 difficulties.  The rise time at low frequencies is long enough that any 
 50Hz/60Hz interference from power line related current flow can modify the 
 trigger point and influence the measurement.  The fast rise time signals 
 proposed for evaluating the measurement setup get around that, but then of 
 course you are measuring a wideband signal, which rather misses the point 
 of the original goal of measuring vs. frequency, so at some point after 
 verifying the setup basics you will have to go back to narrow band 
 signals. 
  
 A 5370 is a somewhat coarse instrument for this type of measurement, a VNA 
 which has a suitable lower measurement frequency would probably be more 
 suitable. 
  
 --  
 Chris Caudle 
  
  
  
  
  
  
  
 ------------------------------ 
  
 Message: 6 
 Date: Mon, 29 Oct 2018 15:23:49 +0000 
 From: "Dr. David Kirkby" <drkirkby at kirkbymicrowave.co.u 
 To: Tom Van Baak <tvb at leapsecond.com>,   time-nuts at lists.febo.com 
 Subject: Re: [time-nuts] How can I measure time-delay of a cable with 
 	HP 5370B time-interval counter? 
 Message-ID: 
 	<CANX10hDi1yY82fXJZvYDVomnnAX 
 Content-Type: text/plain; charset="UTF-8" 
  
 On Mon, 29 Oct 2018 at 09:43, Tom Van Baak <tvb at leapsecond.com> wrote: 
  
 
 David, 
  
 Just to see if your setup is working: 
  
 1) Set the pulse generator to as fast a risetime as possible; ns or less. 
 Use a low pulse rate (100 Hz is fine). 
  
 
  
 Unfortunately, I don't have such a pulse generator, so I can't run that 
 test. But it is clear the system is sensitive to the trigger levels, so I 
 guess is the problem. I have done all the confidence checks in the manual 
 on this TI counter before and it was fine. 
  
 Also, I am interested in the delay of the cable at low frequencies, as I 
 suspect that might depart significantly from the usual figure based on the 
 "velocity factor". Certainly the impedance of coax  rise at low frequencies 
 because the normal formula 
  
 Zo = sqrt(L/C) 
 is not valid before a few MHz. A more accurate formula is 
  
 Zo = sqrt ( (R + j w L )/ ) / (G + j w C)) 
  
 where R = Resistance per unit length 
 L = inductance per unit length 
 G = Conductance per unit length 
 C = Capacitance per unit length. 
  
 So feeding in short pulses brings the validity of such a test into 
 question. 
  
  
 
 2) Use a BNC tee at the generator, into two equal 2 meter cables, each one 
 into a 5370B input. 
 3) Set manual trigger, 50R, 1.0 V, DC 
 4) Now collect time interval data in block/stats mode. You should see a 
 mean of under +/-1 ns and a stdev in low ps. 
  
 /tvb 
  
 
  
 Thank you. I will look for a pulse generator. I would use the 1 pps from 
 the GPS receiver, but my HP 58503A GPS receiver has decided to pack up. I 
 need to have a look at that, but it is not the highest priority task just 
 now. 
  
 This possible trigger issue metioned by Hal Murray is probably a result of 
 the knobs not exactly lining up with the positions they are in. It is 
 fairly clear that the marker on one of them is vertical at 0  V, but the 
 other is not. I need to try to get the knob back on the shaft in a slightly 
 different position. But they were both set to preset, but it is clear that 
 the reading is sensitive to the trigger points. 
  
 I have a 100 MHz scope, and can borrow a 300 MHz scope, but I don't have 
 anything really fast. 
  
 I have a VNA which can make measurements of phase difference down to 300 
 kHz, but don't trust those because of the fact one calibrates with a 50 ohm 
 load, 50 ohm calibration standards, yet I know the impedance will rise well 
 above 50 ohms at low frequencies. 
  
 I was looking for a different approach than a VNA, to make comparisons with 
 a VNA. 
  
 Dave 
  
  
 ------------------------------ 
  
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