PocketVNA Any idea what its like? - Page 1
Forum section: electronics / rf-microwave

author: mohala
author_rank: Newbie
timestamp: March 28, 2016, 09:26:20 pm
content: Hiya everyone,Long time reader of EEVblog but a short time writer.I have been on a mission to find a low cost VNA for antenna design for the 2.4Ghz bluetooth and wifi band, but the results have been quite limited, with those in MiniVNA Tiny, MegiQ or LA Techniques.Seeing the last two go for over £4000 (or copper mountain which is around $3000 1 port VNA) seam to be a lot of money to let go for a beginner.I eventually found these guys called Pocket VNA, costing $430 or 390 Euros the guys are from what I see are Germany, It looks really interesting from a money point of view.But I was wondering has anyone tested their VNA's before and if you would like to give your opinion on accuracy, build and reliability.It would be really appreciated.The link ishttp://pocketvna.com/Best regardsMo

author: TheSteve
author_rank: Unknown
timestamp: March 28, 2016, 10:03:49 pm
content: I think I'd prefer a used HP 8714C or similar(yes shipping them is expensive...)

author: Koen
author_rank: Frequent Contributor
timestamp: March 28, 2016, 10:08:44 pm
content: Over a similar frequency range and similar price, I own a MiniVNA Tiny and would appreciate it if someone more knowledgeable could compare the two. Thank you !

author: mohala
author_rank: Newbie
timestamp: March 28, 2016, 10:42:14 pm
content: Quote from: Koen on March 28, 2016, 10:08:44 pmI agree I had noticed the MiniVNA Tiny when connected to a tablet you have to press a button to start a single sweep, from the looks of the software on the PocketVNA they have something called "Live Measurement" I'm guessing its a continuous sweep.That maybe an advantage I'n not sure?

author: Bud
author_rank: Super Contributor
timestamp: March 28, 2016, 11:23:41 pm
content: They (cheap ones) all use broadband power detectors at their input, therefore detecting all rf energy at the point of measurement which may cause skewed readings. I'd think they are in a same leage in terms of accuracy.

author: mohala
author_rank: Newbie
timestamp: March 29, 2016, 12:06:52 am
content: I guess its a nice way to start learning antenna design and matching. With a cheap VNA than spending thousands on one, maybe when you build up the experience and looking to go to do work professionally, you could go to the R&S, Aglient or Arintsu VNA's.What you guys think?

author: Bud
author_rank: Super Contributor
timestamp: March 29, 2016, 02:04:12 am
content: It certainly is.

author: Theobald
author_rank: Contributor
timestamp: March 30, 2016, 02:31:06 pm
content: Hi,I use a miniVNA Tiny at work for PCB antenna matching and SAW filter amplitude response in the ISM 868 band. It does the job. The Java application on PC is correct, a good product (at least @ 868MHz).A minor point, it can get very hot, not so good for the reliability, unplug it when unused.Add a Smith chart freeware and you're ready.In the other hand, I've never use a 4000€ VNA, I can't compare.Theo

author: Koen
author_rank: Frequent Contributor
timestamp: March 30, 2016, 08:23:32 pm
content: Hello, I used to let it warm up for half an hour before calibrating and measuring anything. Usually, it then stays close to 50°C.Is disconnecting/reconnecting it to use it cold better ?

author: Theobald
author_rank: Contributor
timestamp: March 31, 2016, 07:38:44 am
content: Hello,no, you're right and that's the point: don't make calibration (open, short, 50ohms trilogy) at room temperature, let it warm up. Again, it's a minor issue, even 4000€ instruments need a warm up !Theo

author: Neganur
author_rank: Unknown
timestamp: March 31, 2016, 09:56:03 am
content: Anritsu has a 1-port USB NVA for antenna measurements, it's fairly affordable and, judging by trying it on a trade show, pretty good too!There's two bandwidth models, 40MHz...4GHz and 150kHz...6GHzDatasheet (3MB):https://www.anritsu.com/en-US/test-measurement/support/downloads/brochures-datasheets-and-catalogs/dwl010872EDIT: found the email with the list price for the 4GHz model, it was 2.8k EUR (price is a year old). Of course that's much more that 400-500 for the PocketVNA.

author: jeffsf
author_rank: Contributor
timestamp: April 05, 2016, 06:47:55 pm
content: Quote from: TheSteve on March 28, 2016, 10:03:49 pmI would too......except that the asking price is generally out of my budget.One option to consider is a VSWR bridge which will give you magnitude, but not phase. For tuning antennas, you often just need the magnitude.If you've got 40 dB of directivity you can probably measure return loss down to about 20-30 dBSee, for example,http://www.anritsu.com/en-us/test-measurement/solutions/en-us/Understanding-directivityWiltron (now Anritsu) makes several models. The higher directivity ones (40 dB) covering up to a couple GHz can be had for $200 with patience.An "SWR Autotester" includes a detector, while an "SWR Bridge" does not.http://exodus.poly.edu/~kurt/manuals/manuals/Other/WILTRON%20SWR%20Autotesters%20&%20Bridges%20Operation%20&%20Maintenance.pdfhttps://www.valuetronics.com/Manuals/ANRITSU-60N50.pdfYou'll also need a signal generator that covers the frequencies of interest, if you don't have one already. Sweep isn't really necessary as you can step through the frequencies of interest.If you've got an RF detector for the range, another option would be a directional coupler. Check Narda, for example. The directivity generally isn't as good as the Wiltron bridges/autotesters, but they can be found for $50 or so, with patience.

author: RadioDude
author_rank: Newbie
timestamp: June 18, 2016, 04:04:51 pm
content: I saw a demonstration of a MegiQ VNA-0440. It works nice and professional and it has UFL calibration also. There is review comparing with Rohde & Schwarz ZVL and MiniVNA:http://www.gsm-modem.de/M2M/wp-content/uploads/2014/04/IoT-M2M-Cookbook-Harald_excerpt.pdfPrice is about €2800.

author: D3f1ant
author_rank: Frequent Contributor
timestamp: August 05, 2016, 08:18:06 pm
content: Anybody end up buying/testing a pocketvna?

author: German_EE
author_rank: Super Contributor
timestamp: August 06, 2016, 01:18:58 pm
content: There is some confusion here about the different VNA names and brands.The MiniVNA only works from 1 MHz to 180 MHz and due to internal limitations in the circuitry cannot indicate the sign of a reactive impedance, you therefore cannot determine if a device is inductive, resistive or capacitive and cannot plot it on a Smith Chart. RF connections are BNC and the computer connection is USB 2The MiniVNA Pro is an upgraded version of the MiniVNA with SMA connectors and it can interface using Bluetooth. This VNA CAN measure the sign of a complex impedance and therefore can display a Smith Chart. Frequency range is 100 KHz to 180 MHz.The MiniVNA Tiny can work from 1 MHz to 3 GHz and has SMA connectors. This VNA can also measure the sign of a complex impedance and Smith Chart software is included. Computer connection is via USB using a Mini-USB connector.Disclaimer: I am a happy MiniVNA owner.

author: D3f1ant
author_rank: Frequent Contributor
timestamp: August 06, 2016, 11:06:39 pm
content: Could some of you guys with experience with usb vna's please chime in over at a similar thread in test equipmenthttps://www.eevblog.com/forum/testgear/vna-recommendations/

author: rfbroadband
author_rank: Unknown
timestamp: August 06, 2016, 11:11:56 pm
content: I would buy a used VNA with better specs. 40dB of dynamic range above 1GHz is simply not acceptable for many cases.

author: cncjerry
author_rank: Unknown
timestamp: August 07, 2016, 07:27:55 pm
content: The problem I had with simple VNA circuits as I tried to build my own before settling on the N2PK VNA, was that they were very broad-band and if you had any local broadcast stations (and I do) then it was worthless. Trying to plot my off center fed dipole and I had peaks and dips and all kinds of problems.So no mater what you buy, I suggest you find something that does precise power measurements with some type of filtering. Many of the low cost VNA units use a signal generator with a directional coupler and an AD8307 for the returned power measurement. In a perfect world, this setup would work fine but the 8307 is reading not only the reflected power from the signal generator, but all the harmonics as well as any broadcast stations, amateurs, etc.The bottom line is I would check any of the VNA units you are considering for problems with broadcast stations. A good indicator of a problem is if they offer a broadcast band filter as an option.One other thing I can add is if you have a sweep generator (any cheap DDS off eBay will work) a directional coupler or resistive bridge, and an RTLSDR dongle, you can get pretty close results to many of the low cost VNA units out there.

author: D3f1ant
author_rank: Frequent Contributor
timestamp: August 17, 2016, 08:19:01 pm
content: This is whats inside a pocket VNA if anybody was curious.

author: borjam
author_rank: Unknown
timestamp: August 18, 2016, 06:40:45 am
content: Quote from: rfbroadband on August 06, 2016, 11:11:56 pmCorrect me if I'm wrong please. If you are designing filters and other microwave circuitry you will need better specs. If you are checking antennas 40 dB should be rather adequate.

author: hendorog
author_rank: Super Contributor
timestamp: August 18, 2016, 11:35:57 pm
content: Quote from: D3f1ant on August 17, 2016, 08:19:01 pmThats cool, thanks for posting it. I just spent some time figuring out how I think it works.Maybe this is all wrong, but here are some things I noticed:RFFC5071 mixer 1 output is 30MHz minimum but goes directly into a 4.8kHz max ADC.http://www.rfmd.com/store/downloads/dl/file/id/27381/rffc5071/5072_data_sheet.pdfhttp://www.analog.com/media/en/technical-documentation/data-sheets/AD7192.pdfThe unbalanced side of several of the GH marked Minicircuits baluns seem to be connected inconsistently compared to the datasheet.Pin 1 & 2 should be ground and pin 3 is the unbalanced signal. I don't know if/how much this matters...http://www.minicircuits.com/pdfs/TCM1-43X+.pdfI can't work out how the bridge circuit works - I think it is R28, R29, R30 and U15 but it doesn't seem to be connected in the way I would expect.I haven't worked out what U2 is doing. My first thought was it was the reference path, but it should be connected to the other switch output of U36 - then switching U36 one way measures the DUT and the other way measures the reference. Instead it is connected to the DUT port.

author: Wirehead
author_rank: Regular Contributor
timestamp: January 12, 2017, 06:47:13 am
content: So - what would be the general consensus?The PocketVNA or the MiniVNA Tiny?I'm looking at building some antennas (1GHz <> 2.4GHz), amateur level, but I do want to have some repeatability and measurements. Big irons are too expensive overhere.Specs are pretty similar for both of them from what I can see..The MiniVNA Tiny has a bit more output power, dynamic range seems to be on par..

author: julianhigginson
author_rank: Frequent Contributor
timestamp: January 20, 2017, 06:32:49 am
content: I think for the money the miniVNA tiny and the pocketVNA are both pretty amazing!I'd pick the pocketVNA, because it's about 100 EUR less than the miniVNA tiny, has a metal case, and specs seem kind of similar... possibly slightly better on the pocketVNA (and miniVNA doesn't have a lot of specs published on the site which I find offputting.I guess, from here, I would speak with the pocketVNA manufacturer about what sort of deal they have for returns, and if that seems OK to you, buy it, run it through its paces in your lab, and see if you think it's worth the money yourself!

author: Wirehead
author_rank: Regular Contributor
timestamp: March 02, 2017, 07:55:56 pm
content: Got the PocketVNA, it's awesome.. The software is fast and easy to use, doesn't install crap, calibration works well, doesn't get too hot,... You can tune antennae in a jiffygreat product

author: julianhigginson
author_rank: Frequent Contributor
timestamp: March 02, 2017, 11:56:09 pm
content: awesome to hear! I pulled the trigger the other week, and mine is due in a few days, too.He did say via email that I could return it (postage at my cost) if it's not right for me, but glad to hear someone else really loves theirs already.

author: Wirehead
author_rank: Regular Contributor
timestamp: March 03, 2017, 01:32:30 pm
content: Yep, works great. Initially made a "general" calibration file to do a quick check over a broad range; and then a couple precision, application specifics.Here's an ADS-B antenna before and after tuning (1090MHz). 1/4wave GP antenne. It was a bit too long initially. Now well tuned.

author: julianhigginson
author_rank: Frequent Contributor
timestamp: March 08, 2017, 06:31:38 am
content: I had some interesting introduction to my pocketVNA, but quite happy with how it's going now.Here's the calibration phase of 2-3G, and then a measurement of a detachable wifi antenna (plus 1.5cm or so of RP-SMA adapter.. maybe I should have compensated that??)

author: rfspezi
author_rank: Regular Contributor
timestamp: March 16, 2017, 10:04:44 am
content: I have analyzed the miniVNA in this thread here:https://www.mikrocontroller.net/topic/351273The implementation of the pocketVNA is almost identical.In the block-diagram you can see how the the resistive broadband bridge works.

author: cncjerry
author_rank: Unknown
timestamp: March 18, 2017, 04:41:40 pm
content: http://www.antennasbyn6lf.com/files/vna_comparisons.pdf

author: michael2
author_rank: Contributor
timestamp: March 23, 2017, 10:36:06 pm
content: I'm owning a 2.0 pocketVNA and I'm disappointed.On its web site is claimed:QuoteThis is overdrawn to the limits in my opinion. The problems are significant temperature drift and insufficient calibration options, especially the S21 calibration is useless in my opinion.Up to 100 MHz this VNA works good. Up to 1 GHz you have to control the ambient temperature to say 2°C to get repeatable readings.For the range up to 2 Ghz you have to be very nitpicking. Additionally to control the ambient temperature very close you have to set up your desired measuring parameters (which should be equal to the calibration procedure) and make continuous measurements for about 20 minutes. Then you can use the accumulating function to get some nice readings.But the range starting at about 2 GHz and exceptionally above 3 GHz is useless in my opinion. Even about 10 minutes after a fresh calibration the readings are drifting like an off-road car in the dessert... Repeatability is not achievable.Another thing is the software. There are a some issues. But software can be fixed and I think the software gets fixed in the future. But it is annoying to live with the issues in the meantime. Maybe I'm a little bit huffy regarding the software...My conclusion? Compared to other products in this area the pocketVNA is currentlynobetter. Other products claim a range to 1 GHz for example and support the claimed range very well. I think with more investments into the software pocketVNA can outperform in the range up to 1GHz in the future. But the range 2 GHZ and above will never work reliably, I think. At least with the actual hardware version.

author: Wirehead
author_rank: Regular Contributor
timestamp: March 24, 2017, 08:04:31 am
content: Did you make sure to let the device warm up before calibrating? As with any VNA, you need to let it warm up before calibrating. Otherwise it will drift...

author: michael2
author_rank: Contributor
timestamp: March 24, 2017, 09:04:00 pm
content: Quote from: Wirehead on March 24, 2017, 08:04:31 amOf course, without warm up for an hour even the 100 MHz range is bad. Stabilization starts about 30 minutes after power up.

author: michael2
author_rank: Contributor
timestamp: March 27, 2017, 07:42:02 pm
content: 1 GHz to 4 GHZ, some scans the last 24 hours. The problems are clearly visible, I think.I wonder, if someone else have this issues too?

author: hendorog
author_rank: Super Contributor
timestamp: March 27, 2017, 08:38:27 pm
content: Quote from: michael2 on March 27, 2017, 07:42:02 pmPerhaps there is no Reference path in these instruments? i.e. Where the Source is measured directly separately to the DUT and then the ratio calculated and put through the calibration.That should minimise the drift.I thought that the green switch in the block diagram posted was for that purpose but it seems not - i.e. alternating between measuring the DUT and the reflection. There is a corresponding switch on the PocketVNA PCB image posted earlier in the thread too.

author: YO5EB
author_rank: Newbie
timestamp: May 12, 2017, 08:20:28 am
content: I have this device. I try to write here yesterday but my message did not reach the Forum. If I can post now, I come back with technical details.

author: eb4fbz
author_rank: Regular Contributor
timestamp: May 29, 2017, 10:14:45 am
content: It has a serious design flaw: the Port 2 return loss is horrible, so the DUT is mismatched and huge ripple can be observed when measuring a coaxial cable loss (S21). How are you supposed to be able to tune a cavity filter with one port so badly terminated?You can find there are two rf paths in parallel, so 25ohm at low frequency and whatever above 1GHz where transmission lines matters. Those RFSW6024 SPDT switches are non-reflective, so ports allways present 50ohm. Look at C128, C118, U2 and U36.Mismatch could be alleviated placing an attenuator at port 2, but it will reduce the measurement dynamic range.

author: michael2
author_rank: Contributor
timestamp: May 29, 2017, 03:11:23 pm
content: Quote from: eb4fbz on May 29, 2017, 10:14:45 amI can confirm this. I contacted the Pocket-VNA owner early this year and provided him an measurement which I now attached to this posting. The answer was disappointing and the problem not understood. I refrained from further discussion because I lost the confidence in Pocket VNA.

author: hendorog
author_rank: Super Contributor
timestamp: May 29, 2017, 06:22:07 pm
content: Quote from: eb4fbz on May 29, 2017, 10:14:45 amYeah I noticed that in the earlier image too. You can see in the diagram of the miniVNA posted by rfspezi how it should be connected.https://www.eevblog.com/forum/rf-microwave/pocketvna-any-idea-what-its-like/?action=dlattach;attach=299771;imageMaybe worth trying to mod it, it should work better as long as that U36 switch is actually being flipped.Edited to fix the link to the image

author: Wirehead
author_rank: Regular Contributor
timestamp: May 31, 2017, 05:11:17 am
content: Curious as to what hardware version you guys have - I have a "version 2" (February 2017)edit: here's what I get when verifying a 3 months old calibration. No issues like the above where values wildly drift.

author: michael2
author_rank: Contributor
timestamp: May 31, 2017, 03:03:29 pm
content: Quote from: Wirehead on May 31, 2017, 05:11:17 amThis looks like a totally different product!What was the frequency span of your measurement?

author: Wirehead
author_rank: Regular Contributor
timestamp: May 31, 2017, 05:13:57 pm
content: Ok, here's some more.. First of all, some HF bands (80meter, 40meter, 20meter). Then VHF (2meter) and UHF (70cm) and finally ADS-B (+- 1090MHz) and 2.4GHz Wifi.When calibrating, I always do 10 average, 10 adc average, no smoothing (smoothing is cheating)When measuring: 10ADC average.

author: michael2
author_rank: Contributor
timestamp: June 01, 2017, 08:08:37 pm
content: This is the type label of my PocketVNA. Please could you provide your label for comparison?

author: Wirehead
author_rank: Regular Contributor
timestamp: June 01, 2017, 08:16:16 pm
content: Yep, same version. Do remember, that whenever you want to do a representative measurement on a vna, you have to calibrate it, with test leads and such. Every time. No exceptions. Also variation in lab temp has a great impact. Such is life with any vna. My calibration checks above are done in semi stable conditions, but above 2 GHz, things get critical.

author: eb4fbz
author_rank: Regular Contributor
timestamp: June 01, 2017, 09:07:46 pm
content: Quote from: Wirehead on May 31, 2017, 05:11:17 amThat's not the issue: you have just checked the calibration accuracy by placing the OSL kit at the Port 1 after calibration, that should be fine even with a 25ohm source impedance if the maths are done properly, that's what the calibration is for (+/- temperature drift). The problem is that having a ~25ohm port 1 impedance will affect the DUT behaviour because of the mismatch, and this can't be corrected by calibration (these things are what makes the professional VNAs expensive). Even measuring a coax cable loss will be error prone because of the S21 ripple generated by the reflections.Unfortunatelly, you can't check the port 1 impedance without another VNA, because port 2 doesn't have reflection measurement capability (it's not a bidirectional VNA, so only S11 and S21 measurements). But it's clear by looking at the PCB that the design arround port 1 (CN2 connector!) is far from ideal.You can check the effect of port 1 matching by measuring a couple of meters long coaxial cable. First calibrate the VNA and measure the coax S21 as usual, save the trace. Then place a 10dB attenuator at port 1, calibrate the VNA again and remeasure the same coax. You will see that measurements doesn't match, and the first one will show a huge ripple. You can use the 10dB pad technique to improve this behaviour, but you will reduce the VNA dynamic range by 10dB.Now imagine trying to adjust or optimize a high Q circuit, like a band pass cavity or duplexer: it will not be possible because it's behaviour will be very different when connected to the VNA. Resonances will change, loss, rejection... You could be able to get the desired response, but it will not work the same way when attached to a 50&50ohm system.If your VNA behaves differently, please take a photo of the PCB to look for the differences.

author: Wirehead
author_rank: Regular Contributor
timestamp: June 01, 2017, 09:23:08 pm
content: Quote from: eb4fbz on June 01, 2017, 09:07:46 pmI'll try to take a picture tomorrow. Bit hesitant to open it up, but hey, for the good cause

author: Wirehead
author_rank: Regular Contributor
timestamp: June 01, 2017, 09:36:28 pm
content: By the way - here's the effect of the VNA warming up.1GHz - 4GHz - 1001 step sweep - 10adc avg - 10 avg cal.Initial calibration was made after warm-up of 4 hours. Then I've let the device settle unpowered, and then let it warm up again. Last measurement is after 4 hours again in exact conditions (yes, nitpicking. Same usb port, cable orientation, connector cleaning, ...) of the load calibration standard. You can see it slowly creeps to the correct value once the device is warmed up.No through measurement yet, and I'll need to get that 10dB pad eb4fbz is suggesting

author: pete463251
author_rank: Newbie
timestamp: June 20, 2017, 01:49:33 am
content: Hi Everyone,Great thread, first time poster here. I wrote antennatheory.com and also launched a kickstarter this month of a 400MHz-2.7GHz 2 port VNA, I'd be thrilled if you checked it out:https://www.kickstarter.com/projects/1913839854/chazwazza-a-low-cost-2-port-400mhz-27ghz-vnaPeople send me the miniVNA and pocketVNA a few times and ask why the one I developed, called the Chazwazza is better. I really liked the comparison referenced earlier (http://www.gsm-modem.de/M2M/wp-content/uploads/2014/04/IoT-M2M-Cookbook-Harald_excerpt.pdf) on page 74, which shows the comparison of the miniVNA to a high end VNA and it doesn't stack up too well.The reason I developed mine was to have a low cost (and accurate!) stand alone device - which means no software to install. I also found I could do integrated automatic calibration, which was a side benefit.My kickstarter will probably fail, so I'm trying to decide if there is enough demand for VNAs out there to do another spin, cost down and wider frequency range but with continued solid accuracy. Feel free to ping me on any of this stuff!ThanksPetep.s. 40 dB of range is more than enough for tuning antennas. It is a rookie move to care if your s11 is less than -20 dB, the effects of the cable and installation in any real environment will alter the antenna. So if your target is s11<-40 dB, your wasting your time! source: me

author: eb4fbz
author_rank: Regular Contributor
timestamp: June 26, 2017, 10:42:20 am
content: Quote from: pete463251 on June 20, 2017, 01:49:33 amYou are right, but i would expect much more from 2-Port VNA than just a VSWR antenna analyzer. For filters and duplexers adjustment you absolutely need >80dB S21 dynamic range, and none of these "amateur" VNAs is able to do so at 1GHz. Besides that, accurate and repeatable calibration is a must, and test ports impedance should be perfectly matched to 50ohm or performance will be severely degraded. I know this is not cheap to achieve at >500MHz, but an inaccurate VNA is a no sense.

author: fcb
author_rank: Super Contributor
timestamp: June 26, 2017, 10:59:01 am
content: Everyone seems to be building 2 port VNA's. My personal view is that this is just because there are now some really nice RF IC's available at low cost, and engineers are thinking "great IC, lets build a 2 port VNA).Even Pico Technology have just built one. They certainly have their uses, but most seem to be destined to become posh VSWR meters.What would be really useful is a USB connected (powered via mains!) 4 port VNA that goes from 300KHz to 6GHz (to replace my aging 8753C).....

author: fcb
author_rank: Super Contributor
timestamp: June 26, 2017, 11:05:58 am
content: And just to add insult to injury. I really don't see why the chazwazza has a crappy display on it, why not just USB it into a PC - better chance of accessing the pretty good performance so far, or at least a USB port.

author: Kalvin
author_rank: Super Contributor
timestamp: June 26, 2017, 12:07:31 pm
content: Quote from: fcb on June 26, 2017, 10:59:01 amThis doesn't go down to 300 kHz but nevertheless inexpensive and nice design with detailed explanation:http://hforsten.com/cheap-homemade-30-mhz-6-ghz-vector-network-analyzer.htmlWith some improvements:http://hforsten.com/improved-homemade-vna.htmlThe design files can be found in the Github.

author: fcb
author_rank: Super Contributor
timestamp: June 26, 2017, 07:57:14 pm
content: That's a really impressive project - might be very interesting if he does a third version.300KHz is overkill - but 30MHz still very usable as the bottom end.

author: Wirehead
author_rank: Regular Contributor
timestamp: August 09, 2017, 08:55:19 pm
content: It seems Martin quietly released a beta version of the new pocketVNA software. Much improved calibration screens and methods.. I'll give it a go tomorrow

author: Wirehead
author_rank: Regular Contributor
timestamp: November 15, 2017, 07:40:47 am
content: Quote from: eb4fbz on June 01, 2017, 09:07:46 pmI found a good site explaining that technique with the attenuator.. Might be interesting for others:https://www.evaluationengineering.com/features/0200loss.htmIt also mentions "The technique is not appropriate for S-parameter VNAs because a full 12-term, two-port calibration inherently will produce accurate results." So the issue could be overcome by not using a pad; but doing a 12-term 2port calibration? Maybe that's why it's in the new beta? Hopefully eb4fbz can chime in

author: xaxaxa
author_rank: Regular Contributor
timestamp: November 15, 2017, 09:45:09 am
content: Quote from: Wirehead on November 15, 2017, 07:40:47 am12-term calibration can't be done on a T/R vna because the second port does not have a signal source and can't measure reflection.Both the miniVNA tiny and pocketVNA are of the T/R (transmission/reflection) type.The full two port version of the xaVNA supports this kind of calibration.

author: Wirehead
author_rank: Regular Contributor
timestamp: November 16, 2017, 08:27:10 am
content: Ok, so hardware limitation of not having a full blown VNA... the 10db pad is a good idea then.Do drop the sales pitch please. No need for that when discussing technical issues.

author: xaxaxa
author_rank: Regular Contributor
timestamp: November 16, 2017, 09:20:55 am
content: Quote from: Wirehead on November 16, 2017, 08:27:10 amNot sure why you would think that was a sales pitch; I was trying to be helpful and clear up some confusion about T/R two port vs full two port, since some manufacturers are vague about it.

author: Jaimon
author_rank: Newbie
timestamp: June 08, 2018, 04:04:23 am
content: I also faced the same problem with calibration , But with modified version of the software " BETA" it works fine...

author: hendorog
author_rank: Super Contributor
timestamp: June 24, 2018, 04:58:32 am
content: Quote from: xaxaxa on November 15, 2017, 09:45:09 amThere is a cal type called one path two port which can do this on t/r network analysers. You need to manually reverse the dut.

author: 0xdeadbeef
author_rank: Super Contributor
timestamp: July 21, 2019, 07:32:27 pm
content: I wonder if there is the verdict on the pocketVNA has changed in the meantime? Is it usable in the 2G range or does it have a design flaw?I figure there is a SW 1.0 available since end of October 2018 but not much development since then.Anyway, for the MiniVNA Tiny, things look even worse. I guess the developers have stopped supporting it after the Chinese copycats took over.

author: OwO
author_rank: Super Contributor
timestamp: July 22, 2019, 05:43:46 am
content: Quote from: 0xdeadbeef on July 21, 2019, 07:32:27 pmThe design flaw is in using those all-in-one phase & log magnitude detector chips. No way you're gonna get good accuracy out of those because of DC, nonlinearity and drift errors. AFAIK all cheap USB VNA's have this problem.Edit: except those Si5351 based cheap 300MHz ones on aliexpress that actually do DSP on the micro.

author: hendorog
author_rank: Super Contributor
timestamp: July 22, 2019, 06:51:21 am
content: Quote from: OwO on July 22, 2019, 05:43:46 amNegative ghost rider, pocketVNA doesn't use that technique either. See the PCB layout and the block diagrams which have been posted above.

author: ogden
author_rank: Super Contributor
timestamp: July 22, 2019, 07:02:59 am
content: Quote from: OwO on July 22, 2019, 05:43:46 amIt is not about detector butfront end design flaw. PocketVNA have no log / magnitude detector but rffc5071 mixer with ad7192 ADC. It is clearlyRF mixing and IF sampling architecture.

author: AF6LJ
author_rank: Unknown
timestamp: July 25, 2019, 05:12:21 pm
content: Not to mention the first time you key a transmitter directly into one, or when a nearby transmitter fires up and blows the snot out of the detector you are not out big bucks or that HP you bought on E-Bay is waiting for you to buy another one to use as a Parts queen.When you know their limitations you can get some use out of the cheap ones.

author: KD0CAC John
author_rank: Frequent Contributor
timestamp: July 25, 2019, 11:22:46 pm
content: 1st off Hi SueI have several antenna analyzer / VNAs , MFJ-269 , Sark 110 , and a MiniVNA Pro .I keep all inputs covered with my calibration loads , either a 50 ohm load , short or open - probably in that order for effectiveness .I started doing that after repairing several RF test gear and overloaded inputs MFJ 259s , TimeWave TZ-900 etc.TimeWave is a friend of mine , club member and we talked about that , and ever since - capped all inputs .

author: AF6LJ
author_rank: Unknown
timestamp: July 29, 2019, 08:13:20 pm
content: Long time no see.Good to see you again.Indeed this stuff is really fragile.