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Re: US Manufacturers?
When I worked on GPS initial design we had a rigorous spec for the noise
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temperature of several of the receivers. This was in the late 1970's. We could not make the spec with anything from the US at the time but could using an NEC part from Japan. At the time this was a national security issue with the fear of "hijacked' devices from the Soviet Union or elsewhere with unwanted "codes" embedded in them. This was WELL before the present-day fakes so common from China. We ultimately had to get a letter from the Pentagon, yes, the Pentagon (!!), to use the NEC part. I saw the letter. Be glad this issue is just political and not linked to national security. Dave - W?LEV On Tue, Aug 29, 2023 at 6:38?PM Jim Lux <jimlux@...> wrote:
On 8/28/23 11:23 AM, drfuka@... wrote:--Howdy,project that is regulated by The Build America Buy America Act and NDAA889 *Dave - W?LEV* --
Dave - W?LEV |
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Re: US Manufacturers?
I was just speaking with a fellow who does such work and, unsurprisingly, his first question to me was "How many initially and per year and what is the budget?".
It might wind up cheaper renting a Keysight/Anritsu/Copper Mountain commercial unit once all of the qualified vendor paperwork (which is also not free) gets settled. Of course none of them are made in USA either. 73, Don N2VGU |
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Re: NanoVNA for 120 ohm Twin wire Balanced lines
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:--I have found that blocks of Styrofoam are excellent for this use; *Dave - W?LEV* -- Dave - W?LEV |
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Re: US Manufacturers?
On 8/28/23 11:23 AM, drfuka@... wrote:
Howdy, The Buy American Act probably falls in the exception: "the items to be procured or the materials from which they are manufactured must be present in the United States in sufficient and reasonably available commercial quantities of a satisfactory quality. The provisions of the act may be waived if the head of the procuring agency determines the act to be inconsistent with the public interest or the cost of acquiring the domestic product is unreasonable. " The items to be procured aren't present in the US. In my government funded job, we buy things from foreign mfrs all the time: Think Rhode+Schwarz test equipment, SpaceWire test equipment, or even more mundane, fancy RF cables. Yes, you have to fill out a form saying why you can't get it from a domestic supplier. NDAA889 is potentially more troubling, but I think it covers only "Telecommunications Equipment and Services" and the NanoVNA doesn't fall into that bucket. |
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Re: Not available at Ali Express / Zeenko
Order from R&L Electronics:
* No connection other than ordered quite a number of Chinese electronics including the NANOVNAs and TinySAs / Ultra. My credit card issued on my CU will not deal with AliExpress. . . . nor will I. Dave - W?LEV On Tue, Aug 29, 2023 at 5:55?PM Manfred Mornhinweg <manfred@...> wrote: I placed a lot of orders on AliExpress over several years, including the-- *Dave - W?LEV* -- Dave - W?LEV |
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Re: Not available at Ali Express / Zeenko
I placed a lot of orders on AliExpress over several years, including the NanoVNA, TinySA, etc. Most of the time it worked fine. Until recently! AliExpress sent my last three orders through a little bad logistics company called BlueExpress, that doesn't serve my area, and these orders never arrived. The tracking says "delivery attempt failed", and in e-mail communication with that logistics company they told me that they are holding the parcels, and want me to travel to a distant city to pick them up!
I complained to AliExpress, requesting refunds, and they refused, falsely claiming that the parcels are waiting in my local post office. Of course they are NOT there, and after asking BlueExpress by e-mail, they told me that they do not deliver to post offices. I forwarded that e-mail to AliExpress, and then they judged that it was all my fault, and closed the case with no refund, and no further appeal possible. I lost my money and my time. So AliExpress is no longer an option for me. It would be good for sellers in China to offer their goods on more places. Too many just concentrate on AliExpress. But AliExpress is giving trouble to too many people lately. We need sales sites that give the buyer and seller options for shipping, that allow choosing the actual company that will do the shipping. For me the postal service works fine, but AliExpress doesn't offer that anymore. Just "Standard" or "Economy" shipping, and AliExpress chooses which shipping company to use - and for my last three orders they chose one that can't deliver to me! Sorry to let my steam off here in the forum - but I think the matter is of interest to possible future buyers of NanoVNAs, and certainly to the maker! |
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Re: NanoVNA for 120 ohm Twin wire Balanced lines
On Tue, Aug 29, 2023 at 04:12 AM, Bob Ecclestone VK2ZRE wrote:
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 |
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Re: NanoVNA for 120 ohm Twin wire Balanced lines
Hi Arun,
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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 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? |
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Re: USB vs no USB readings Plots change...
Hello Mark,
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I do not pretend to be an expert here, but I will make a few observations. 1. Many posts in this group have already noted that connecting a NanoVNA to a computer via USB cable results in an effective counterpoise being created which will change the tuning of the system under test. 2. Most professional VNAs are mains powered so you can not do a "battery vs USB" measurement comparison. Nothing to do with "laboratory grade" equipment. 3. Even professional grade battery operated VNAs have significant physical "bulk" compared to a NanoVNA so measurements will be disturbed less than those of the physically smaller sized NanoVNA. 4. Try measuring a 2M or 70cm hand held radio antenna fitted directly to the S11 port. Do the measurement holding the NanoVNA in your hand and with the NanoVNA sitting on a large cardboard box. You will notice a significant difference due to your body affecting the measurement. So all I can suggest is fitting a ferrite to your USB cable to decouple it. Wind several turns through a large ferrite tube or toroid. Maybe one at each end. I would suggest type 43 ferrite, but please, anyone with more knowledge here, please step in. The main thing is you need to try to "kill" the counterpoise effect created by your USB cable. HTH...Bob VK2ZRE On 29/08/2023 3:07 am, Mark KQ4EKK wrote:
Thanks to all for their help with this. |
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Re: NanoVNA for 120 ohm Twin wire Balanced lines
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. |
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Re: USB vs no USB readings Plots change...
Unbalanced antenna should have sufficiently large ground plane to minimize impact of transmission line. Objects near the antenna can change characteristics of the antenna. Such as people and things in a room that act on radio waves at the frequency under test. Some people recommend consideration of objects within ten wavelengths for their impact.
There's a good chance many VNA lab experiments do not fully account for environmental impact on antennas. VHF antennas may be too large to correctly build indoors, and UHF or higher antennas may not be constructed with enough precision to truly evaluate the design. Commercially, antennas are range tested and can be measured when installed at the customer location. VHF range testing means a lot of land. Customer's on-site measurements should be made and reviewed carefully. The other thread discusses balanced antenna measurement. |
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Re: US Manufacturers?
Yeah, indeed... so onto question 2... anybody in the US want to build
one that can be sold to federal agencies or federal contractors? It involves some paperwork if haven't built for them before. On Mon, Aug 28, 2023 at 5:06?PM Jim Allyn - N7JA <jim@...> wrote:
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Re: NanoVNA for 120 ohm Twin wire Balanced lines
I have used the NANOVNAs quite successfully to test 300-ohm and 410 to
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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 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.-- *Dave - W?LEV* --
Dave - W?LEV |
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Re: USB vs no USB readings Plots change...
Hi Mark-
What's causing the data to change when you plug the unit into the USB cable is the fact that adding the USB connection causes that USB cable (and whatever else it's connected to) to become part of the antenna system. Therefore, the impedance that the network analyzer is looking into has actually changed. That's why battery operation is such a nice thing! :-) Tom AE5I |
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Re: USB vs no USB readings Plots change...
Connect the VNA over Bluetooth serial. You can buy the adapters for a few $.
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How to attach the adapter has been discussed a number of times here. On Mon, 28 Aug 2023 at 21:51, Mark KQ4EKK <kq4ekk+groups@...> wrote:
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Re: USB vs no USB readings Plots change...
Mark KQ4EKK
Already understood and thanks. Maybe a better question is: Is there a method to isolate the VNA from the PC when connected via the USB to kill (choke?) the effect. I am just experimenting and learning here, by no means am I a veteran on vna usage.
Thanks Dave. |
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Re: NanoVNA for 120 ohm Twin wire Balanced lines
I would suggest one of the small transformers made by Mini-Circuits.
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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? |
Donald S Brant Jr
Jim Allyn - N7JA
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