Products > Test Equipment
Sub $1000 VNA for antenna matching
dermeister:
Thanks a lot for all of the replies! I am tending towards getting a LiteVNA64 now. It seems like it will be sufficient for my current needs and also good tool to learn VNA basics.
joeqsmith:
Just for another reference, here is some magnet wire with an OD of 1.12mm. This is slightly smaller than UT047 at 1.19mm (OD of outer conductor).
Bud:
Get a VNA that has Port Extensions feature. Not just Electrical Delay correction. Some VNAs call the simple electrical delay adjustment "Port Extension" which is confusing. Those are different features. Electrical delay is a correcting value which is applied to the measured phase. It does not correct for the connection loss and the calibration plane remains where it was. Port Extension shifts the calibration plane to the DUT terminals by taking in account the delay and loss, recalculating the error terms for the test port.
joeqsmith:
--- Quote from: dermeister on November 27, 2022, 05:55:26 pm ---Thanks a lot for all of the replies! I am tending towards getting a LiteVNA64 now. It seems like it will be sufficient for my current needs and also good tool to learn VNA basics.
--- End quote ---
IMO all of these low cost VNAs are great tool for learning and you can hardly go wrong with any of them. Between the LiteVNA and the original NanoVNA, you pretty much have the basics covered. Below 300MHz, the original NanoVNA offers some advantages I have yet to see matched. The Lite on the other hand is fast, higher frequency range, somewhat adjustable output level. Dislord has done a very good job with the Lite's firmware. While I have no use for 90% of the features, it's proven to be very stable.
Downside with all of these are the output is not level and it's a squarewave. You don't get a lot of the features you would with a higher end system (built-in bias T's, input and output attenuators, more complex calibration schemes, two port one path...). You also are not going to get the dynamic range, they have higher noise, poor connectors.... For passive circuits, much of it won't matter. Active is another story. I made a video showing an simple circuit to demonstrate the possible problems with the squarewave drive (attached if interested). Obviously, if you are trying to measure an amplifier and the VNA's output is not known and level, you can run into problems quick.
FYI on the Lite.
The first one I bought worked well and met the suppliers specs. A friends had very high noise. They bought a second and shipped me theirs. Their second one also had high noise. After some testing, I found the Lite was very sensitive to the input voltage level from the USB port. Basically, to get around it, I made a USB cable with a diode in series with the power to lower it. This solved the problem. Thanks to Dislord, you can use it to measure narrow band devices (crystal filters) but it is dog slow. It's low frequency performance is poor (much higher noise) compared with the original NanoVNA. One of the Lite's my friend purchased came with a bad USB cable. It supports a CF card. I don't have a use for it but did try it out. First thing that happened, the card fell inside the case and I had to take it apart to fetch it. $120.... You may find several posts on the standards supplied with them. I've never looked at what was supplied with the Lite. Any test data I have shown with these low cost VNAs has used the ideal model (standards are considered perfect), and using the short and open supplied with the V2Plus4. For the load, I bought a lot of 8 mini-circuit terminators that I characterized using a set of Agilent standards and my Agilent PNA. One had really good RL which I set aside. The second best is what I use.
points2:
--- Quote from: joeqsmith on November 27, 2022, 06:59:14 pm ---... Below 300MHz, the original NanoVNA offers some advantages I have yet to see matched.
--- End quote ---
hello joeqsmith,
you mention that over low frequencies, the nanoVNA is OK.
I have a nanoVNA-H4, I confirm that point, when I just want to see the self resonant freq of a MLCC X7R (sorry for this basic example :-) )
Recently I get bored to wait for the nanoVNA to sweeeeeeeep (too long), so I bought a LibreVNA => much faster ! Cool ! The LibreVNA freeware : top cool too (requires some time to understand the features but... top ! )
Problem : when I tested a basic X7R, having a SRF @ 300kHz => the LibreVNA was blind vs its SRF due a too high noise (wavvy curve around magnitude=-40dB) over the weird frequency range : mini 100kHz to 1.29Mhz, then, the measurement was in line with the product characteristics (strange).
Is it a common drawback of LibreVNA & others (except the nano) to struggle to do clean measurements over the low-end frequencies ? or if my vendor replaces my LibreVNA by a new one, I'll have no issue ? (a bad item, it can happen) ; I'm waiting for feedback from him, he's waiting for feedback from the manufacturer...)
After reading this thread & the other in link above, I'm a bit confused to discover that the ability of VNAs to do clean measurements over low frequencies is "tricky".
Fortunatly, my nanoVNA does the job. But it is so slow...
When I look at the other VNAs on the market, I end up to the conclusion that, regarding low freq measurements, we have (vs price) : the nanoVNA (100eur) and then... the cheapest seems to be the Siglent SNA5002A (8000eur). What a gap ! :-)
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