On Wed, Aug 23, 2023 at 03:10 PM, Geoff Peters - AB6BT wrote:
OK, I see what you mean, and I suspect the the VF can vary by 1% over the
length of the cable.
I will test with a piece of CAT6 by cutting one wire and reconnecting at one
foot intervals.
The VF for the TDR test will be the same no matter what length you cut the CAT6 cable. VF for a specific type of cable will vary by manufacturer and even different between production runs by the same manufacturer. But for what you are measuring this should not be a concern. Take a measured length and then adjust VF to get the same calculated length using the TDR. Then you have the VF to use for with that specific type of cable. Roger
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For some reason, my messages are not making it to the email chain...they are in the groups.io online...
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On 8/23/2023 3:01 PM, Roger Need via groups.io wrote: On Wed, Aug 23, 2023 at 01:52 PM, Geoff Peters - AB6BT wrote:
In this case, what I'm trying to determine is the minimum distance I can
measure to a fault.. I used 4.8mm to simplify this discussion, I'm not sure
what you mean by "only in steps of 1 so this is the limiting factor." . I
understand that the actual distance/step is VF dependent.
The resolution is 4.8 mm but the accuracy will be worse because you cannot enter the VF to more than two digits. So if the VF is 69.5 % and you have to enter 69 or 70% that will affect the calculation because the VF used in the NanoVNA is off by 0.5 %. But for practical purposes it will be close enough.
BTW - if you select the Format as "Real" in the menu the line will move to the center of the display and shorts and open can be determined by seeing if the pulse is above or below the line just like with a TDR test box.
Roger
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OK, I see what you mean, and I suspect the the VF can vary by 1% over the length of the cable.
I will test with a piece of CAT6 by cutting one wire and reconnecting at one foot intervals.
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On Wed, Aug 23, 2023 at 01:52 PM, Geoff Peters - AB6BT wrote:
In this case, what I'm trying to determine is the minimum distance I can
measure to a fault.. I used 4.8mm to simplify this discussion, I'm not sure
what you mean by "only in steps of 1 so this is the limiting factor." . I
understand that the actual distance/step is VF dependent.
The resolution is 4.8 mm but the accuracy will be worse because you cannot enter the VF to more than two digits. So if the VF is 69.5 % and you have to enter 69 or 70% that will affect the calculation because the VF used in the NanoVNA is off by 0.5 %. But for practical purposes it will be close enough. BTW - if you select the Format as "Real" in the menu the line will move to the center of the display and shorts and open can be determined by seeing if the pulse is above or below the line just like with a TDR test box. Roger
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Sigi,
Yes, I have a piece of CAT6 cable to test. I removed the jacket at 1 foot intervals for about an inch. I will test by cutting 1 wire at a time at each location and see what I measure.
Geoff
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On 8/23/2023 2:02 PM, Siegfried Jackstien wrote: take 10 inch of speaker wire.. that should show almost similar numbers.. if thats the case then yes you can trust it
dg9bfc sigi
Am 23.08.2023 um 22:52 schrieb Geoff Peters - AB6BT:
Roger,
I sent a reply but it hasn't shown up so here's take 2...
In this case, what I'm trying to determine is the minimum distance I can measure to a fault.. I used 4.8mm to simplify this discussion, I'm not sure what you mean by "only in steps of 1 so this is the limiting factor." . I understand that the actual distance/step is VF dependent.
For example, I have a CAT6 cable with an open green wire. I have calculated the VF as I know the physical length of the cable, 300 feet/91.44 meters.
Using a NanoVNA-H4 I measure the distance to the fault at about 240mm.
So the question is...can I trust that number?
Geoff
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take 10 inch of speaker wire.. that should show almost similar numbers.. if thats the case then yes you can trust it
dg9bfc sigi
Am 23.08.2023 um 22:52 schrieb Geoff Peters - AB6BT:
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Roger,
I sent a reply but it hasn't shown up so here's take 2...
In this case, what I'm trying to determine is the minimum distance I can measure to a fault.. I used 4.8mm to simplify this discussion, I'm not sure what you mean by "only in steps of 1 so this is the limiting factor." . I understand that the actual distance/step is VF dependent.
For example, I have a CAT6 cable with an open green wire. I have calculated the VF as I know the physical length of the cable, 300 feet/91.44 meters.
Using a NanoVNA-H4 I measure the distance to the fault at about 240mm.
So the question is...can I trust that number?
Geoff
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Roger,
I sent a reply but it hasn't shown up so here's take 2...
In this case, what I'm trying to determine is the minimum distance I can measure to a fault.. I used 4.8mm to simplify this discussion, I'm not sure what you mean by "only in steps of 1 so this is the limiting factor." . I understand that the actual distance/step is VF dependent.
For example, I have a CAT6 cable with an open green wire. I have calculated the VF as I know the physical length of the cable, 300 feet/91.44 meters.
Using a NanoVNA-H4 I measure the distance to the fault at about 240mm.
So the question is...can I trust that number?
Geoff
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Roger,
Mainly I'm trying to determine the minimum distance to a fault that I can measure.
I understand that the 4.8mm number is dependent on the VF, I was only trying to keep things simple for this discussion.
How reasonable is it to believe I can resolve a distance to within one step?
We use CAT6 cables for interconnecting audio equipment that gets pretty rough treatment on the road. Right now I have a quad CAT6 cable with an open green wire in one of the cables. I have determined the VF as I know the physical length of the cable.
Using NanoVNA-H4, I measure the break to be at about 240mm. So the real question is can I trust that number?
Geoff
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On 8/23/2023 1:21 PM, Roger Need via groups.io wrote: On Wed, Aug 23, 2023 at 10:07 AM, Geoff Peters - AB6BT wrote:
How does calibration affect the Thansform measurement? You need to be calibrated over the frequency range that you select. However there is calibration interpolation used on some NanoVNA's, like the -H and -H4, so you can arrow the frequency range if you want to measure longer cables. However for best accuracy calibrate over the frequency range that accommodates your cable length. The lower frequency should be kept at 50 kHz and the upper frequency limit , number of sample points and velocity factor entered will determine the maximum length that can be measured.
If I set the stimulus start and stop to 50KHz and 1.5GHz the transform maximum
length is shown as 19.36m. If I set the sweep to 401 points what resolution
and accuracy can I expect, provided that I have the VF entered correctly.
1936mm/401 equals just over 4.8mm.
Your calculation is correct. However you won't be accurate to 4.8 mm becasue the velocity factor you enter (in percent) is only in steps of 1 so this is the limiting factor.
Roger
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On Wed, Aug 23, 2023 at 10:07 AM, Geoff Peters - AB6BT wrote:
How does calibration affect the Thansform measurement?
You need to be calibrated over the frequency range that you select. However there is calibration interpolation used on some NanoVNA's, like the -H and -H4, so you can arrow the frequency range if you want to measure longer cables. However for best accuracy calibrate over the frequency range that accommodates your cable length. The lower frequency should be kept at 50 kHz and the upper frequency limit , number of sample points and velocity factor entered will determine the maximum length that can be measured.
If I set the stimulus start and stop to 50KHz and 1.5GHz the transform maximum
length is shown as 19.36m. If I set the sweep to 401 points what resolution
and accuracy can I expect, provided that I have the VF entered correctly.
1936mm/401 equals just over 4.8mm.
Your calculation is correct. However you won't be accurate to 4.8 mm becasue the velocity factor you enter (in percent) is only in steps of 1 so this is the limiting factor. Roger
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Yes, that's what I do, not a problem...
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On 8/23/2023 12:59 PM, Clyde Spencer wrote: Make sure you enter the VF as a percentage not a decimal value. EXAMPLE 60
not .60
*Clyde K. Spencer*
On Wed, Aug 23, 2023 at 1:08?PM Geoff Peters - AB6BT <AB6BT@...>
wrote:
I have a couple questions regarding using the Transform function to
measure length of a cable.
How does calibration affect the Thansform measurement?
If I set the stimulus start and stop to 50KHz and 1.5GHz the transform
maximum length is shown as 19.36m. If I set the sweep to 401 points what
resolution and accuracy can I expect, provided that I have the VF entered
correctly.
1936mm/401 equals just over 4.8mm.
Thanks,
Geoff -- AB6BT
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Make sure you enter the VF as a percentage not a decimal value. EXAMPLE 60 not .60 *Clyde K. Spencer* On Wed, Aug 23, 2023 at 1:08?PM Geoff Peters - AB6BT <AB6BT@...> wrote: I have a couple questions regarding using the Transform function to
measure length of a cable.
How does calibration affect the Thansform measurement?
If I set the stimulus start and stop to 50KHz and 1.5GHz the transform
maximum length is shown as 19.36m. If I set the sweep to 401 points what
resolution and accuracy can I expect, provided that I have the VF entered
correctly.
1936mm/401 equals just over 4.8mm.
Thanks,
Geoff -- AB6BT
|
I have a couple questions regarding using the Transform function to measure length of a cable.
How does calibration affect the Thansform measurement?
If I set the stimulus start and stop to 50KHz and 1.5GHz the transform maximum length is shown as 19.36m. If I set the sweep to 401 points what resolution and accuracy can I expect, provided that I have the VF entered correctly.
1936mm/401 equals just over 4.8mm.
Thanks,
Geoff -- AB6BT
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Re: some Nano VNA SAVER 40m antenna graphs
That will be a very interesting comparison test!
I hope you publish all the details and measurements.
(Great choices of antennas, too. My full-wave horizontal loop is terrific.)
--
Doug, K8RFT
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some Nano VNA SAVER 40m antenna graphs
Getting Ready for the new
**** MidAtlantic 40m NBEMS net ****
testing: Saturday and Sunday 10 AM EDT on 7068 kHz (vfo)
coverage over a 300 mile radius from Philadelphia
THOR 22 check in
THOR 56 traffic (new alpha mode: w1hkj.com/alpha)
Hope to have the net begin by October 7/8 2023
Need 5-8 net control ops from the MidAtlantic region
I now have three 40m antennas to compare prop paths
1) Traditional Inv V dipole, center fed with 1:1 BALUN 66 ft
2) Full one-wave horizontal loop (140 ft)
3) 34 ft alum tubing Vertical (lashed to a tall tree) with two above gnd 30 ft radials
and matching coil at base (like an inverted T )
I had to mess a bit with the length of vertical to get it resonant where I wanted it.
de k3eui barry Aug 22 2023
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Nuno, I was pretty happy with my NanoVNA-F V2 until it randomly died on me. It lasted nearly 2 years though and had zero issues with it before it died. I took a gamble and purchased the SV4401A because I wanted more accuracy (and range) out of a portable VNA.
The SV4401A is *not* light nor compact. So far, I'm very happy with my unit. The firmware is fairly stable, so I have no complaints.
I purchased mine from E-Bay from a China seller. I got mine in about 8 days which was pretty quick.
-Nick, k7cj
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I forgot to add this link
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On 8/21/23 8:45 AM, Leif M wrote: Likewise. I would recommend V2 Plus4 or V2 Plus4 PRO from an official store. There are several other version but I like V2 Plus4. Today perhaps PRO version. Battery lasts a long time and results are good enough. If the tool works at 4GHZ, it will surely be good at 50MHz and 1GHz. I am not totally satisfied with PC software. It is usable but not well finished.
Then there is the VNA6000.
The only potential downside to the V2 is that they are more sensitive to ESD, because they have a monolithic RF switch at the input.
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Likewise. I would recommend V2 Plus4 or V2 Plus4 PRO from an official store. There are several other version but I like V2 Plus4. Today perhaps PRO version. Battery lasts a long time and results are good enough. If the tool works at 4GHZ, it will surely be good at 50MHz and 1GHz. I am not totally satisfied with PC software. It is usable but not well finished.
Then there is the VNA6000.
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i have finaly got my pc to tato the vna,ready to load fw,can anyone tell me what FW has the biggest fonts with the most save slots,thanks.
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Is not easy as you said. It needs to be new design and higher speed components. See link:
FC
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Roger Need
Barry K3EUI
