NanoVNA are they any Good?

Discussion in 'Amateur Radio News' started by M1MRB, Feb 2, 2020.

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  1. AD0QK

    AD0QK Ham Member QRZ Page

    I've got both an MR100 and a nanoVNA. The MR100 I got several years ago. It has issues with the output from time to time and it sometimes gets stuck on max VSWR (10:1). I use my notebook with software built for each of them and get really nice pictures of the sweeps. I would tend to rate the nanoVNA above the MR100 for sure. I love both of them for what they can tell me about my antennas.

    I've got a G5RV Junior antenna as a center fed inverted L (more or less) and I want to tune it better. I got useful readings from both and compared them. However, I did that in the shack and I am pretty sure I'll get some different readings at the feed point. I've got a current balun some fifteen feet from the transition to the 450 ohm window line so that ought to be a superb place to connect. I can run them off my notebook. If I need extended time I can run an extension cord around the house to the measuring point. What a fantastic tool for us ham radio folks!
     
  2. N3HKN

    N3HKN Ham Member QRZ Page

    Does it work as well as the MFJ 259C? I may have missed that message but it is something I can relate to. I do not have one (too $$) but it seems to be a popular and thus a good reference. I have seen cavities from dental x-rays but I doubt that I will ever see one of the big metallic ones. The final 10% of performance ,and getting contest scores, is the last thing I want. I just want to see where the resonance is, what the SWR is and some idea of that I have to do to fix it, IF anything is wrong. Of course, I need to see when I make a mistake or self-create a bad connection. Simple stuff. I will leave Mr. Smith to others as a curiosity.
     
    W9WQA likes this.
  3. N0TZU

    N0TZU Platinum Subscriber Platinum Subscriber QRZ Page

    My guess is that you should stick with a dedicated antenna analyzer. They are pretty simple to operate and are ruggedly built to be used outdoors.

    That’s not the case with the Nano. It can do a whole lot more, but is more complex to set up and use and is more delicate with tiny SMA connectors. You really need to use a stylus with it, and changing the frequency span of interest dramatically could require a recalibration for most accurate results (which needs little short, open and load terminations).

    Having used it for a while, I consider it to be a miniature portable bench instrument which can be pressed into limited service outside if necessary.
     
    KE8JK likes this.
  4. KE8MVY

    KE8MVY Ham Member QRZ Page

    I really like mine and I like how useful it across so many bands for the cost. Getting the software working is not easy, but I would not want to use it without the software. I can save sweeps for future use too. What I've found interesting, is using really wide sweeps of existing antennas and finding unusual sweet spots in them I didn't know existed. If one has an older design unit, it would be nice to see a experiment to see how well the measurements match.
     
    VK6FD likes this.
  5. M5RJC

    M5RJC XML Subscriber QRZ Page

    At this price it is also a useful component to embed in projects. I am using one to self-tune a homebrew auto AMU without having to transmit. The VNA is connected to an Arduino via a USB host shield.
     
    N0TZU likes this.
  6. N0TZU

    N0TZU Platinum Subscriber Platinum Subscriber QRZ Page

    Cool idea! I for one would like to see how you did that. Perhaps you could write it up?
     
  7. M5RJC

    M5RJC XML Subscriber QRZ Page

    Hi Bob

    It's all over the bench ATM so it's not really ready to share ... it will continue to develop for a while yet, however the key points are :
    • The VNA is switched in line (as opposed to the Tx/Rx) by a coax relay - I would like to make this automatic RF-switched but haven't implemented that yet
    • The VNA connects to an Arduino Uno via a USB host shield using the standard libraries
    • The VNA protocol is a simple serial one that is easily converted to C++ by looking at the Python example code that is available on Github
    • The Arduino also acts as a frequency counter (through a x16 prescaler)
    • The Arduino has a I2C connected EE memory to store settings for each 10Khz segment in the ham bands
    • There are 2 switched banks of inductors in binary multiples, plus a similar bank of switched capacitors. The AMU proper is configured for a balanced feed as I'm feeding dipoles/doublets and this avoids compromising with baluns. Getting accurate binary multiples for the L's and C's has proved the hardest part so far, as if they are not accurate the tuning process is disrupted by random jumps in the values.
    • The current design (for proof of concept) is using cheap Chinese relay boards controlled by MCP23017 I2C I/O expanders. These will be replaced by a custom PCB once the design stabilizes. I would not use the current setup above about 25W but obviously this can be improved with the right relays at a later stage.
    • The tuning is done using a Nelder-Mead optimization method to adjust the L's and C's to minimize SWR. The initial start point is the centre of each band and several iterations will be done with different L and C starting values to get the best SWR without the optimization taking too long. After finding a good result for the band centre, the adjacent frequencies use the solution as the start point, making the tuning much faster. Finally the result is stored for future reference - when transmitting, the stored values are retrieved based on the frequency counter. At the moment the L banks are adjusted in parallel, so both inductors have the same value, but there may be some mileage in allowing fine-tuning of the L values separately to offset any asymmetry in the antenna itself.
    • I have only worked on 1 band to date to keep things simple - on 20m the whole band is tuned in 10Khz segments in about 30 seconds.
    • Finally after tuning, the Arduino enters sleep mode to avoid injecting RF noise into the Rx - currently it needs to be re-woken by a button press, but this should also be done by detecting RF
    Much still to do !

    73
    Rick
     
    N0TZU likes this.
  8. W9WQA

    W9WQA Ham Member QRZ Page

    for anyone who hasnt seen one, a poor pix of my 6btv vertical. 80 not showing up onn left as it did yesterday. im NO EXPERT and scuse the lousy focus.
    scanned from 50 khz to 30 mhz left to right.
    yellow "pointer" at left is 80 mtrs,no response today. others at 40,20,30,15 ,10.
    green mess is the smith chart.
    i know very little of this.
    just started tinkering...fwiw.

    better pix next and ill get my triband rubber duck...
    this a $50 nanovna. scans up to 1500 mhz.
    just told you all i know...
     

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  9. N0TZU

    N0TZU Platinum Subscriber Platinum Subscriber QRZ Page

    Very impressive!
     

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