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NanoVNA for 120 ohm Twin wire Balanced lines

Arun All Messages By This Member #33918 Has anyone used a NanoVNA to characterize a Twin wire twisted Balanced line like say a CAN bus line or an ISO-SPI balanced 120 ohm line? If so what interface hardware has been used or is recomended?
KENT BRITAIN All Messages By This Member #33920 I would suggest one of the small transformers made by Mini-Circuits. You can get both the unbalanced to balanced transformation and 50 Ohms to XXX per your needs. I have been using their 50-75 Ohm transformers for years to test video products. Kent toggle quoted message Show quoted text On Monday, August 28, 2023 at 02:01:45 PM CDT, Arun <arunkumar1@...> wrote: Has anyone used a NanoVNA to characterize a Twin wire twisted Balanced line like say a CAN bus line or an ISO-SPI balanced 120 ohm line? If so what interface hardware has been used or is recomended?
Donald S Brant Jr All Messages By This Member #33923 On Mon, Aug 28, 2023 at 03:45 PM, KENT BRITAIN wrote: I have been using their 50-75 Ohm transformers for years to test video products. I can vouch for the quality of Mini-Circuit products, I have used them in MIL SATCOM projects. 73, Don N2VGU
W0LEV All Messages By This Member #33925 I have used the NANOVNAs quite successfully to test 300-ohm and 410 to 450-ohm balanced lines at HF. The size of the NANOVNAs is small enough to not have any (extremely little) influence on the measurements so long as it is not connected to ANYTHING and is resting on a dielectric material and placed well away from anything "large" that is conducting. Oh yes, and "no touchie". Something I can not do with my HP8753C, even with the proper transformers - they should be idolators like a balun or unun. Dave - W?LEV toggle quoted message Show quoted text On Mon, Aug 28, 2023 at 7:46?PM KENT BRITAIN <WA5VJB@...> wrote: I would suggest one of the small transformers made by Mini-Circuits. You can get both the unbalanced to balanced transformation and 50 Ohms to XXX per your needs. I have been using their 50-75 Ohm transformers for years to test video products. Kent On Monday, August 28, 2023 at 02:01:45 PM CDT, Arun < arunkumar1@...> wrote: Has anyone used a NanoVNA to characterize a Twin wire twisted Balanced line like say a CAN bus line or an ISO-SPI balanced 120 ohm line? If so what interface hardware has been used or is recomended? -- Dave - W?LEV -- Dave - W?LEV
Greg Strickland All Messages By This Member #33929 Echoing what Dave posted, I agree it would be best to physically locate Nano VNA at the antenna feed point. This could be physically dangerous or impossible. And how to view or save the measurement? I agree about impact of nearby objects on the antenna. Logical next step is a transformer (aka balun). Now you will need to know characteristics of the balun, or successfully move the calibration measurement plane beyond it. Practicality and safety may result in the balun located at the transmitter end of the balanced transmission line in the transmitter room. But now are you measuring the antenna and transmission line as a system? I think the antenna characteristics or precise transmission line characteristics should be known before doing that. And if you already know that... Presumably for amateur radio and commercial HF and VHF, motorized remote controlled antenna matching networks may be "flown" at the feed point, which may be a elevated high above ground, with coax and matching network monitoring/control cable running from the transmitter room to the antenna feed point. btw- the other night, I noticed I was slightly de-tuning a high Q resonant circuit with my hand nearby, and this was at 2 MHz.
Bob Ecclestone VK2ZRE All Messages By This Member #33931 Hi Arun, I can vouch for Mini Circuits transformers. I had Mini Circuits build some custom 100 Ohm balanced hybrid splitters for a VDSL broadband startup project in Australia. We used 100 Ohm Cat5 cable for the "last mile" and these were used to split one physical VDSL port into two isolated VPN ports. The splitters consisted of one of their standard 50 Ohm unbalanced hybrid splitters with 50-100 Ohm balancing transformers on each of the three ports, all in a 16 pin DIL package. Excellent performance over 1MHz-30MHz, better than 26dB between output ports if I recall. It is your choice, but the general consensus on these forums seems to be to use a centre tapped balanced secondary. You can then chose to connect the centre tap to the 50 Ohm unbalanced port ground or not. You will need to make up an appropriate cable termination jig and to make up your own O-S-L-T terminations for calibration at your chosen test impedance. Be aware that how you support the cable will affect the measurements. Just be consistent about how you support and orient the cable if you intend to compare various results. If you intend to use one of the NanoVNA computer apps, then a ferrite decoupled USB cable is also highly recommended to minimise counterpoise effects. Regards...Bob VK2ZRE toggle quoted message Show quoted text On 29/08/2023 5:01 am, Arun wrote: Has anyone used a NanoVNA to characterize a Twin wire twisted Balanced line like say a CAN bus line or an ISO-SPI balanced 120 ohm line? If so what interface hardware has been used or is recomended?
Donald S Brant Jr All Messages By This Member #33933 On Tue, Aug 29, 2023 at 04:12 AM, Bob Ecclestone VK2ZRE wrote: Be aware that how you support the cable will affect the measurements. I have found that blocks of Styrofoam are excellent for this use; polystyrene is a pretty good dielectric and the foam is 99% air so even better. 73, Don N2VGU
W0LEV All Messages By This Member #33937 Dry discarded corrogated shipping boxes also work well. Dave - W?LEV On Tue, Aug 29, 2023 at 12:25?PM Donald S Brant Jr <dsbrantjr@...> wrote: On Tue, Aug 29, 2023 at 04:12 AM, Bob Ecclestone VK2ZRE wrote: Be aware that how you support the cable will affect the measurements. I have found that blocks of Styrofoam are excellent for this use; polystyrene is a pretty good dielectric and the foam is 99% air so even better. 73, Don N2VGU -- Dave - W?LEV -- Dave - W?LEV
Brian Beezley All Messages By This Member #33940 On Tue, Aug 29, 2023 at 11:41 AM, W0LEV wrote: Dry discarded corrogated shipping boxes also work well. I used to use cardboard to support things until I found these 1 MHz specs for cardboard with a density 0.5 ounces per cubic inch: dielectric constant 6, loss tangent 0.04. By contrast, styrofoam type 103.7 has a dielectric constant of 1.03 and a loss tangent of 0.000021. At 3 GHz the loss tangent is 0.0001. Brian
W0LEV All Messages By This Member #33941 Possibly the εr rating of the corrugated paper, itself, is well above unity, which I seriously doubt. But a large box is pretty much all air with an εr miniscually larger than unity. Dave - W?LEV toggle quoted message Show quoted text On Tue, Aug 29, 2023 at 7:03?PM Brian Beezley <k6sti@...> wrote: On Tue, Aug 29, 2023 at 11:41 AM, W0LEV wrote: Dry discarded corrogated shipping boxes also work well. I used to use cardboard to support things until I found these 1 MHz specs for cardboard with a density 0.5 ounces per cubic inch: dielectric constant 6, loss tangent 0.04. By contrast, styrofoam type 103.7 has a dielectric constant of 1.03 and a loss tangent of 0.000021. At 3 GHz the loss tangent is 0.0001. Brian -- Dave - W?LEV -- Dave - W?LEV
W0LEV All Messages By This Member #33942 One can easily MEASURE the εr of the corrugated box material. Build a parallel plate capacitor using aluminum foil, single or double-sided FR-4 PCB, or some other creative set of flat conductors. Measure the capacitance using the NANOVNA (Smith Chart) with only air between the plates. Then slip in and fill the volume between the plates with your unknown material. Again measure the capacitance. Since the capacitance is a linear function of εr, the εr of the unknown material is the ratio of the two measurements, unknown over air measurements of the two capacitances. What's more, you can measure the εr as a function of frequency as well. Dave - W?LEV On Tue, Aug 29, 2023 at 7:23?PM W0LEV via groups.io <davearea51a= [email protected]> wrote: Possibly the εr rating of the corrugated paper, itself, is well above unity, which I seriously doubt. But a large box is pretty much all air with an εr miniscually larger than unity. Dave - W?LEV On Tue, Aug 29, 2023 at 7:03?PM Brian Beezley <k6sti@...> wrote: On Tue, Aug 29, 2023 at 11:41 AM, W0LEV wrote: Dry discarded corrogated shipping boxes also work well. I used to use cardboard to support things until I found these 1 MHz specs for cardboard with a density 0.5 ounces per cubic inch: dielectric constant 6, loss tangent 0.04. By contrast, styrofoam type 103.7 has a dielectric constant of 1.03 and a loss tangent of 0.000021. At 3 GHz the loss tangent is 0.0001. Brian -- Dave - W?LEV -- Dave - W?LEV -- Dave - W?LEV -- Dave - W?LEV
Brian Beezley All Messages By This Member #33943 Corrugation should lower the dielectric constant and loss of any material roughly in proportion to its air content. So corrugated cardboard should have better specs than the uncorrugated cardboard specs I quoted. However, the electric field of the object under test will be maximum where it touches the support. It's there where the dielectric properties of the support matter. Increasing the size of a supporting box is unlikely to reduce the effect of lossy box material. Using lossy materials with high dielectric constant is fine for casual measurements. But it pays to use something more transparent to electric fields when the measurement is important. This also applies to the magnetic field. Avoid anything ferromagnetic or conductive nearby. Brian
W0LEV All Messages By This Member #33944 Large styrofoam blocks are the "standard" in professional communities. At home, with all the RF test equipment, I use either corrugated boxes or an empty 50-gallon rubbish can. I could buy large styrofoam blocks from Hobby Lobby (at least they used to carry them), but I'd have trouble storing them with wifie. Dave - W?LEV toggle quoted message Show quoted text On Tue, Aug 29, 2023 at 7:56?PM Brian Beezley <k6sti@...> wrote: Corrugation should lower the dielectric constant and loss of any material roughly in proportion to its air content. So corrugated cardboard should have better specs than the uncorrugated cardboard specs I quoted. However, the electric field of the object under test will be maximum where it touches the support. It's there where the dielectric properties of the support matter. Increasing the size of a supporting box is unlikely to reduce the effect of lossy box material. Using lossy materials with high dielectric constant is fine for casual measurements. But it pays to use something more transparent to electric fields when the measurement is important. This also applies to the magnetic field. Avoid anything ferromagnetic or conductive nearby. Brian -- Dave - W?LEV -- Dave - W?LEV
Jim Lux All Messages By This Member #33945 On 8/29/23 1:55 PM, W0LEV wrote: Large styrofoam blocks are the "standard" in professional communities. At home, with all the RF test equipment, I use either corrugated boxes or an empty 50-gallon rubbish can. I could buy large styrofoam blocks from Hobby Lobby (at least they used to carry them), but I'd have trouble storing them with wifie. We use blocks covered with static dissipative film (Amstat, etc.) The surface resistance is sufficiently high that it doesn't load the RF system, but it also prevents the charge that inevitably accumulates on foam from destroying your electronics.
Brian Beezley All Messages By This Member #33946 For large, high-Q coils, some crystal set builders use a styrofoam cake dummy like this: Styrofoam is as close to air as anything solid I know of. It may be tedious to set up, but if you can support whatever you're measuring with fishing line you should be able to eliminate all support interaction. But you still have to worry about other stuff in the room. One time I was trying to accurately measure the Q of a large coil with my HP 4342A Q meter. I was astounded to find that I had to remove myself several feet and crouch down to eliminate interaction with my body. Even then I wasn't sure I got rid of it all. I couldn't read the meter from any farther away. Brian
Greg Strickland All Messages By This Member #33975 Feature creep alert Could sensitive measurements be easier if Nano VNA had an optical transmitter and companion receiver, or an internal memory to record "screen shot" or measurements on a timer?
Stan Dye All Messages By This Member #33986 Some users have installed bluetooth adapters, which can give the same isolation result. These use the serial port available inside the nanovna. You could also use a pair of opto-isolators on the internal serial port lines, and connect a serial control port through them to give electrical isolation. The cable wires would still be there, which may still have some minor effect, even though they are electrically isolated. Unfortunately you can't do an optical approach with the USB port, since it requires electrical connectivity for power, etc. Adding a true optical control port that uses optical cable is possible, but would likely be more than the cost of the nanovna. On Thu, Aug 31, 2023 at 4:24?AM Greg Strickland <greg@...> wrote: Feature creep alert Could sensitive measurements be easier if Nano VNA had an optical transmitter and companion receiver, or an internal memory to record "screen shot" or measurements on a timer?

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