Re: Estimating coaxial cable length - using TDR
Jim VE7RF
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Re: Estimating coaxial cable length - using TDR
I don't know the OP's reasons for wanting to know but I'd think it useful
for knowing how much is used on a run, how much is left on a reel and for
tracking down faults to think of just a few.
"Precise" is of course variable by application, from back when 10b2
ethernet was a thing and dinosaurs roamed the earth within a metre was
excellent because I can eyeball and inspect for faults at that sort of
distance, YMMV.
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On Mon, 12 Jun 2023, 07:35 Jim VE7RF, <jim.thom@...> wrote: I'm trying to fathom the reason for knowing the exact physical length of
a piece of coax, or it's exact electrical length. What are you trying to
do here, phase yagis on 14 mhz.... or building a 4 square vertical array
for 80m ?
Even if building stacked yagis, and the coax is all coming off the same
reel, it's a moot point. All that is required is equal lengths of coax
from the L network, to each yagi.
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Re: Estimating coaxial cable length - using TDR
I'm trying to fathom the reason for knowing the exact physical length of a piece of coax, or it's exact electrical length. What are you trying to do here, phase yagis on 14 mhz.... or building a 4 square vertical array for 80m ?
Even if building stacked yagis, and the coax is all coming off the same reel, it's a moot point. All that is required is equal lengths of coax from the L network, to each yagi.
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Re: Anybody happens to know VF of this cable ?
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Thank you, Jim. Much appreciated. -- Rich WB2GXM------ Original message------From: Jim LuxDate: Sun, Jun 11, 2023 8:33 PMTo: [email protected];Roger Need via groups.io;Cc: Subject:Re: [nanovna-users] Anybody happens to know VF of this cable ?On 6/11/23 4:23 PM, Richard Spohn wrote: Ok, you said "there are several ways to determine the actual VF of a cable using a NanoVNA". WHY did you stop there? Dispense with the attitude and just TELL US what these methods are!!- 1) use the NanoVNA to sweep and find out where 1/4 wavelength is (i.e. peak in S11 magnitude). Knowing the frequency where it's 1/4 wavelength, you can compare to free space wavelength. 2) Use the NanoVNA to measure the phase shift of the reflection at multiple frequencies, and then fit a straight line to the measurements, after unwrapping the phase. 3) Use the TDR function of the NanoVNA. All of these use a known length of cable, then you measure the electrical length of that length, and the ratio is the VF.
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Thanks Roger and everyone else that is helping me learn on this journey. Eventually I'll get it all locked down and be able to pay it forward I hope ?
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Re: Anybody happens to know VF of this cable ?
On 6/11/23 4:23 PM, Richard Spohn wrote: Ok, you said "there are several ways to determine the actual VF of a cable using a NanoVNA". WHY did you stop there? Dispense with the attitude and just TELL US what these methods are!!- 1) use the NanoVNA to sweep and find out where 1/4 wavelength is (i.e. peak in S11 magnitude). Knowing the frequency where it's 1/4 wavelength, you can compare to free space wavelength. 2) Use the NanoVNA to measure the phase shift of the reflection at multiple frequencies, and then fit a straight line to the measurements, after unwrapping the phase. 3) Use the TDR function of the NanoVNA. All of these use a known length of cable, then you measure the electrical length of that length, and the ratio is the VF.
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On Sun, Jun 11, 2023 at 12:28 PM, Mike Anderson/KF?AWL wrote:
Ok now, is there a easy way to figure out the resonance of the antenna?
I'm useing a different whip and ground plane so the factory (height) on the
coil is going to be off so I'm wondering if there is a easy way to get a idea
of where the coil is setting the antenna up at.
Mike, W2AEW has an excellent series of videos on how to use the NanoVNA to measure and adjust antennas. I think you will find this one worth watching. Roger
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Re: NanoVNA-H not seen by windows11 (no com port)
#nanovna-h
On Sun, Jun 11, 2023 at 12:22 PM, <ciungan.marius@...> wrote: I have a NanoVNA-H wich used to work under W10 with Nanosaver app. After
upgrade to W11, when I connect the NanoVNA to usb port nothing happens, no new
com port is seen under device manager.
Wonder if anyone had the same problem. Any help its welcome.
thank you.
If you can't see the NanoVNA-H as a COM port in Windows 11 after plugging it in that means that the driver is not installed. Windows 11 should install it automatically but sometimes it fails to load. It could be sitting in your "Optional Updates" and you need to select it for installation. Use the search box to find "Windows Update" and select it. Then go to "Advanced Settings" and select "Optional Updates" (see screenshot below). You may find the driver is there waiting to be installed. Some drivers will not install in Windows 11 because "Memory Integrity" is on and the driver does not meet Microsoft safety standards. If you turn off Memory Integrity the driver can then be installed. Roger
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Re: Anybody happens to know VF of this cable ?
Very good point about actual VF vs published VF. There are several ways to quickly get the actual VF of the cable using a NanoVNA but the OP ("Anne") doesn't like posts that go beyond specifically answering her question.
OK, humor me and tel me TWO of several ways to ":get the actual VF of the cable using a NanoVNA"
PS
According to last test - my " digital ( other superlatives intentionally removed ) RG6" VF is .66 !
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Re: Estimating coaxial cable length - using TDR
Roy J. Tellason, Sr
It looks as "this TDR" subject has life of its own,,,
The Agilent article will take me some time to digest...
At present I am trying to "run the source code of nanoVNASaver" in Qt debug mode.
Tentatively I will try to make "TDR" and "TDR display " to match...
My last test - finding known length of my "fancy digital RG6" of VF . 82 ( VF value thanks to the group replies, appreciate that )
matches my inch stick when I set the VF to .66 !
So... is it real or Memorex?
Is my fancy RG6 mislabeled and it is really plain RG6 of .66 VF?
Where is the problem ?
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Re: Anybody happens to know VF of this cable ?
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Ok, you said "there are several ways to determine the actual VF of a cable using a NanoVNA". WHY did you stop there? Dispense with the attitude and just TELL US what these methods are!!------ Original message------From: Roger Need via groups.ioDate: Sun, Jun 11, 2023 3:05 PMTo: [email protected];Cc: Subject:Re: [nanovna-users] Anybody happens to know VF of this cable ?On Sun, Jun 11, 2023 at 11:59 AM, Joe WB9SBD wrote:
Now something to remember,
The VF can be FAR from that spec.
I have seen Brand New cables that were different THAN THE SPECIFIED VALUE.
And as cables age, and it seems this stuff is OLD, that it changes
sometimes a LOT as it gets older!
Joe, Very good point about actual VF vs published VF. There are several ways to quickly get the actual VF of the cable using a NanoVNA but the OP ("Anne") doesn't like posts that go beyond specifically answering her question. Roger
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Re: Estimating coaxial cable length - using TDR
On Saturday 10 June 2023 02:04:13 pm Roger Need via groups.io wrote: For more details on how the S11/IFFT method of TDR works this tutorial by Agilent is quite informative. ?It includes details on why "windowing" the data is necessary, how to determine the upper stop frequency required based on estimated cable length, why the lower start frequency should be close to DC and other considerations.
Some intersting reading, there. -- Member of the toughest, meanest, deadliest, most unrelenting -- and ablest -- form of life in this section of space, ?a critter that can be killed but can't be tamed. ?--Robert A. Heinlein, "The Puppet Masters" - Information is more dangerous than cannon to a society ruled by lies. --James M Dakin
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Re: When I connect NanoVNA Saa-2N to the USB-port
Sorry, it was the USB-cable. Should have used the one included.
-Oddleiv
s?n. 11. juni 2023 kl. 14:33 skrev Oddleiv Tungland <oddleiv@...>:
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s?n. 11. juni 2023 kl. 14:27 skrev Oddleiv Tungland <oddleiv@...>:
the display starts to flicker.
-Oddleiv
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Ok now, is there a easy way to figure out the resonance of the antenna?
I'm useing a different whip and ground plane so the factory (height) on the coil is going to be off so I'm wondering if there is a easy way to get a idea of where the coil is setting the antenna up at.
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NanoVNA-H not seen by windows11 (no com port)
#nanovna-h
Hello all,
I have a NanoVNA-H wich used to work under W10 with Nanosaver app. After upgrade to W11, when I connect the NanoVNA to usb port nothing happens, no new com port is seen under device manager.
Wonder if anyone had the same problem. Any help its welcome.
thank you.
Marius
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Sorry, didn't read your post correctly. Make sure you save the calibration, Then look on the left of the display to make sure you recall the saved calibration.
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On 2023-06-11 11:16, Mike Anderson/KF?AWL via groups.io wrote: Ok new question.
I'm following the setup in the beginner's guide for process of calibration, get it done according to the guide and try to verify with the Smith chart . I screw my open to port 1 trace 1 (trace 0 is my swr trace) were I did the calibrate and according to the guide it should go to the far right of the Smith chart. It dont, it just sits in the same place. What am I doing wrong here?
I'm following it step by step!
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Far right is very high resistance, far left is very low resistance. Your open calibration looks good!
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On 2023-06-11 11:16, Mike Anderson/KF?AWL via groups.io wrote: Ok new question.
I'm following the setup in the beginner's guide for process of calibration, get it done according to the guide and try to verify with the Smith chart . I screw my open to port 1 trace 1 (trace 0 is my swr trace) were I did the calibrate and according to the guide it should go to the far right of the Smith chart. It dont, it just sits in the same place. What am I doing wrong here?
I'm following it step by step!
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Re: Anybody happens to know VF of this cable ?
On Sun, Jun 11, 2023 at 11:59 AM, Joe WB9SBD wrote:
Now something to remember,
The VF can be FAR from that spec.
I have seen Brand New cables that were different THAN THE SPECIFIED VALUE.
And as cables age, and it seems this stuff is OLD, that it changes
sometimes a LOT as it gets older!
Joe, Very good point about actual VF vs published VF. There are several ways to quickly get the actual VF of the cable using a NanoVNA but the OP ("Anne") doesn't like posts that go beyond specifically answering her question. Roger
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Re: Anybody happens to know VF of this cable ?
Now something to remember,
The VF can be FAR from that spec.
I have seen Brand New cables that were different THAN THE SPECIFIED VALUE.
And as cables age, and it seems this stuff is OLD, that it changes sometimes a LOT as it gets older!
Joe WB9SBD
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On 6/11/2023 1:07 PM, Jim Shorney wrote: Yes, well, the point was to have the OP go the last mile to get the information by following the archive link and maybe learn a thing or two in the process. This probably comes from having a mother who was a teacher. She had some clever ways of tricking me into learning things...
73
-Jim
NU0C
On Sat, 10 Jun 2023 20:31:21 -0700
"Jim Lux"<jimlux@...> wrote:
foam, 82% VF
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Re: Anybody happens to know VF of this cable ?
Yes, well, the point was to have the OP go the last mile to get the information by following the archive link and maybe learn a thing or two in the process. This probably comes from having a mother who was a teacher. She had some clever ways of tricking me into learning things... 73 -Jim NU0C On Sat, 10 Jun 2023 20:31:21 -0700 "Jim Lux" <jimlux@...> wrote: foam, 82% VF
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Mike Anderson/KF?AWL
Roger Need
Jim Shorney