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Thread: Low cost VNA - thoughts?

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    Default Low cost VNA - thoughts?

    https://www.ebay.ca/itm/Handheld-2-8....c100005.m1851

    I know.

    But if doing up a preselector or a set of 3 cans (per side) in a duplexer, are you going to hear the extra 0.2 - 0.6dB, which you might recover from a $40,000 unit? Yes, it adds up. But even if out by 1dB, is it worth $40,000 more money? I can tell you guys right now, I can't hear 1dB of improvement when listening to an analog system. Digital, perhaps it will affect things when signals are on the edge, but not by much.

    If anyone has tried this thing, I'm curious how you found operation/benefit vs. a $40K+ unit.


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    rtl-sdr.com recently did a review on one of those types of VNAs, I don't think that exact one. But, I can't seem to find it on the site. I tried with googling just the site, and there is a hit, but I just can't get to the article. You might have better luck.

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    For the price, I will use this thing for most measurements unless doing test equipment calibrations. The FieldFox is WAY too expensive to fix if I screw up. If I smoke the cheapo VNA I'll just buy another. I'll let someone else let the smoke out of the $50k instrument. Thank God the Aeroflex is pretty robust. I have done some stupid things in the past. (don't tell the boss)
    Apparently NOT a radio professional.

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    I sponsored the xavna as a kickstarter project. It is open source, and well built.

    https://xaxaxa-dev.com/xavna.cppsp

    It stacks up well against the work $20K Rohde & Schwarz, generating the same smith charts for antennas we swept between 137 MHz and 2.5 GHz. A steal for $275 US.

    Regards,
    Phil

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    I've ordered one of the units in the OP which should be here soon. I've read lots of good reviews about them but be aware that there are now some versions that don't have any shielding around the RF units. These are usually the ones with a white PCB.

    I'll post some test results one mine turns up on the slow boat...

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    I have read a lot of comments about there being varying quality levels, but have never seen details on reliable sources for the good ones.

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    I just ordered one of these gadgets also. Looking forward to testing it against an S412E.

    Reviews look promising and should make a good enough excuse for a VNA I can keep in a go-bag (that does not cost as much as a new Corvette).

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    Couple of local purchased these units as 'get out of jail' test kit and so far so good, minor issues above 350mhz (as noted) but still very much useful device.

    Also I believe you can connect to a laptop or tablet for bigger screen but I have not actually seen this in action yet.

    If you want to spend more dollars the mini-vna has been out for sometime and available on aliexpress in plastic and ally cases
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    I got one. They are very nice for what they are. They read favorably when compared to multi-kilobuck lab devices, and they read directly on a Smith chart which is nice.

    As for quality, there is some variation, read the descriptions and look at the pictures carefully. Make sure that the unit has battery included, some vendors omit them for shipping reasons. I bought mine from Amazon and it was one of the cheapest, but turned out to be one of the best ones. There are 3 "quality" levels - unshielded, copper foil shielded, and proper metal can shielding. Mine was one of the latter, which is the best of the 3. Also, make sure it comes with cables and a calibration kit, with 3 parts - short, open, and load. The top cover trim of the units available is either black or white, and some sites claim that the white ones with the gecko logo are the poorer quality units. I am not sure if that is true, but if you research the above items, that seems to be what matters.

    The Amazon vendor I got mine from was "GuckZahl Direct", and it was only $48.94 out the door, w/shipping, tax, etc. It came from China in about 2 weeks.

    Yes, there are several different PC programs that put up a full-screen display and button layout for better seeing and reading the displays. It comes with a driver that emulates a serial port, my Win7 machine found the driver "online" during the device search, so far I have been using that default MS driver with success. There are also several versions of firmware you can update the unit to, you have to short 2 contacts to bring the unit up in "DFU" mode (I'm not going there...) and you can re-flash the unit. There are several firmware versions, the big difference seems to be the high-end frequency (using 3rd and 4th harmonics) to get a base fundamental version up to 300 MHz, and harmonic versions going up to 900MHz and even 1.5 GHz, but performance kind of falls apart above 1GHz. I have downloaded the flash updates, but have not yet gotten around to loading any of them yet.

    They are well worth the price, credit-card sized, and with a touchscreen, they are 1GHz spectrum analyzers, tracking generators, and return-loss bridges. They can display directly in SWR, AC impedance of an antenna network, and function like an antenna analyzer, with added phase display. They can also perform TDR functions and determine cable length, etc. Very cool!

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    Not a VNA, but I acquired a Keysight E4406 VSA Transmitter Tester a couple of years ago at a very low price.

    https://www.keysight.com/en/pd-10000...z?cc=US&lc=eng

    It's proved useful for many testing tasks.

    These can be had on Ebay for very little money.

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    I also picked one up; I believe it's identical to the one Alpha described.

    Through the exposure/experience I've had in this industry over the years, I was never able to use/access a VNA. I'm not one to pretend I know what I'm doing, if I'm clueless. I understand what a VNA is used for and how it can benefit my projects/PM checks, but I am not entirely familiar with the proper calibration of the unit. I think we should discuss this, as it's critical to the operation/accuracy/results we're looking at.

    The SOLT (Short, Open, Load, Through) method seems to be the most common standard. But is the test done with the coaxial jumper attached to the port? Which port should we use, and why?

    This may seem like a series of stupid questions. But, traditionally, unless one had $40,000+, access to a VNA and performing basic tasks such as a SOLT calibration and interpreting the results, was not something many of us could appreciate/be aware of.

    I'm very much interested in learning more about the functionality of the unit and what all of the data means. Oh, and Alpha, the firmware update is easy. Everything needed (and the flash files) are here.

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    As far as calibration goes, with a commercial unit you calibrate at the end of the jumper and if you remove/change the jumper you need to re-calibrate. They typically come with a very high quality 2-3ft jumper.

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    Quote Originally Posted by Mars View Post
    I also picked one up; I believe it's identical to the one Alpha described.

    Through the exposure/experience I've had in this industry over the years, I was never able to use/access a VNA. I'm not one to pretend I know what I'm doing, if I'm clueless. I understand what a VNA is used for and how it can benefit my projects/PM checks, but I am not entirely familiar with the proper calibration of the unit. I think we should discuss this, as it's critical to the operation/accuracy/results we're looking at.

    The SOLT (Short, Open, Load, Through) method seems to be the most common standard. But is the test done with the coaxial jumper attached to the port? Which port should we use, and why?

    This may seem like a series of stupid questions. But, traditionally, unless one had $40,000+, access to a VNA and performing basic tasks such as a SOLT calibration and interpreting the results, was not something many of us could appreciate/be aware of.

    I'm very much interested in learning more about the functionality of the unit and what all of the data means. Oh, and Alpha, the firmware update is easy. Everything needed (and the flash files) are here.
    Mars,

    Once I get mine off the slow boat from China, I will compare calibration and measurements between it and the VNA that I have access to. I will also make a couple write ups on how to perform calibrations and a couple different quick test setups. I'm sure it would be helpful for more than just you to have a couple cheat sheets to setup a few quick good to go / nope, it's totally fucked test routines.

    -TM

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    Quote Originally Posted by Mars View Post
    The SOLT (Short, Open, Load, Through) method seems to be the most common standard. But is the test done with the coaxial jumper attached to the port? Which port should we use, and why?
    You zero with the jumper cable you are using in place to subtract it from the measurement. If you are connecting directly to the cable under test (CUT), then the cal tool goes on the VNA port. If you are connecting to the CUT with a jumper, the cal tool goes on the end of the jumper.

    I always get a chuckle out of the cal tools with their precision OPEN and precision SHORT ports on them. But, after seeing these measurements being done by tower crews that don't know what a short or open is, I understand the purpose. These guys are great at climbing towers, doing wonderful, neat, professional work getting cables from the poly to the antenna. Everything is perfectly assembled, but they have no idea what it is. So, the test equipment for proofing the lines is geared towards them since a record of the return loss and distance to fault is how they get paid. The test equipment has to be as close to an appliance as possible so untrained guys can run it.

    That said, I have seen crews put the cal tool at the end of the new line they just installed as part of the cal procedure prior to taking the money measurement. They call out from the ground "OPEN!", response yelled "OPEN ON" (wait wait wait), "SHORT!", response "SHORT ON", (wait wait wait), "LOAD!", "LOAD ON",,,, It makes you wonder who trained them.
    Bow wow wow yippie yo yippie yay

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    I've ordered one of the NanoVNA-F units with metal case from China. Different RTOS based firmware.

    There are discussion groups active on:
    https://groups.io/g/nanovna-users
    https://groups.io/g/nanovna-f

    These products appear to be in early days of development. There is a V2 NanoVNA with dual oscillators to extend frequency range higher apparently coming soon.

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    Quote Originally Posted by Bill_G View Post
    That said, I have seen crews put the cal tool at the end of the new line they just installed as part of the cal procedure prior to taking the money measurement. They call out from the ground "OPEN!", response yelled "OPEN ON" (wait wait wait), "SHORT!", response "SHORT ON", (wait wait wait), "LOAD!", "LOAD ON",,,, It makes you wonder who trained them.
    Even better when they take the load up to troubleshoot but grab the wrong line and connect the load to a transmit line.
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    Quote Originally Posted by cyrus View Post
    Even better when they take the load up to troubleshoot but grab the wrong line and connect the load to a transmit line.
    Yep. And because it didn't turn to charcoal after they realize their mistake, they think nothing is wrong, continue to use it to cal, and then wonder why they can't hit their spec'd RL requirements.
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    Quote Originally Posted by Bill_G View Post
    Yep. And because it didn't turn to charcoal after they realize their mistake, they think nothing is wrong, continue to use it to cal, and then wonder why they can't hit their spec'd RL requirements.
    I've seen this many times. One fellow wanted to borrow my gear without troubleshooting his own gear. I insisted we do some basic troubleshooting first and found his DIN female load was blown. Figured he would borrow mine but I said no way, use your male load with an adaptor as I don't trust you.

    Another crew wasn't cleaning their otdr landing cable every time they used it and their results were getting worse and worse over time until they started rejecting complete runs of fiber that had already been pulled. Took two warranty claims before the manufacturer came on-site, failed their landing cable and charged them for the reels.

    I've got an Anritsu but unfortunately it doesn't do HF. The price on these units is cheap enough that I might grab one for sweeping hf antennas.
    Cyrus

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    Quote Originally Posted by Bill_G View Post
    Yep. And because it didn't turn to charcoal after they realize their mistake, they think nothing is wrong, continue to use it to cal, and then wonder why they can't hit their spec'd RL requirements.
    That's one of the persistent immutable Rules of the Universe taught to me by one of my RF mentors. ALWAYS check your dummy load impedance before use! Make sure it wasn't turned to charcoal last time you or someone else used it. Make sure the oil didn't leak out of the Bird!

    Mars, if you haven't figured it out by now, calibration is pretty easy, you install the 3 pieces and select the SOL calibrations, and loop the cable in to out for the "Thru" test. The "Isolation" test requires a more complicated set-up to calibrate, so that calibration is usually omitted. I saw a video or explanation of it somewhere, if I find it again, I'll add the link to the thread.

    As Bill_G said, you calibrate out the jumper/cable you are using to connect the device to a cable or antenna you want to test, then remove the antenna and do the calibration using SOL with as much of the cable and any "T" or elbow joints in place, and you end up zeroing them out by executing a cal with the 3 SOL parts in place of the actual antenna you want to test. The idea is to subtract as much of the test cabling, etc. as possible.

    Keep in mind antenna sweep testing this way isn't bulletproof, since you aren't really simulating the body of the HT and the counterpoise your hand and arm represent. Like the imaginary lower half image of a quarter-wave antenna, the HT frame and the capacitive coupling of the frame to your hand and arm form the other half of the antenna image. For instance the APX UHF single band antenna I swept had a good return from about 400 to 540 MHz, the peak was about 520 MHz or so. However, the AC impedance of the antenna by itself was about 70 Ohms so that mismatch was due to the lack of ground plane/counterpoise, mostly. In fact, some of the earlier antenna designs used odd impedances, like 33, 62 or 75 Ohms to better match what the HT and user's arm represented. These were in the days of the "studly" (pre BNC/SMA) HT antennas.

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    On a side note, I was informed a 3Ghz version of the VNA is coming out shortly based on the same theory but newer thinking.

    Can not confirm if the 350Mhz limitation is now closet to 1Ghz which would make the unit more usable at 400mhz. Here's hoping.
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    Well. my NanoVNA-F order was cancelled by the Ebay vendor who could not fulfill the order. I've placed a new order directly with the developer, and am waiting now for shipment.

    These must be gaining in popularity.

    The new version with alternate LOs is being worked on now, promising greater range at the high end.