WTB MiniVNA Tiny - Page 1
Forum section: electronics / general

author: mayor
author_rank: Regular Contributor
timestamp: August 02, 2018, 10:47:26 pm
content: Looking for MiniVNA Tiny or Tiny+. Or another reasonably priced VNA.

author: Wolfgang
author_rank: Super Contributor
timestamp: August 03, 2018, 12:54:58 am
content: What about this one:https://www.sdr-kits.net/introducing-DG8SAQ-VNWA3?A lot of my ham colleagues have one and they like it.

author: mayor
author_rank: Regular Contributor
timestamp: August 03, 2018, 01:01:30 am
content: Thanks for the suggestion. Need at least 15khz to 2.4ghz range.

author: Wolfgang
author_rank: Super Contributor
timestamp: August 03, 2018, 01:22:50 am
content: Well, not an easy choice. The "in-spectrum analyzer" VNAs from Siglent or R&S dont meet your lower frequency limit, and if you want something usefulyou will probably end up with a few k€ at least. 15kHz to almost 3GHz is met by a Keysight E5071 without bias tees (then you have 9kHz), or by a E5061 3L5 (5Hz),but these machines are pro class and really expensive.Maybe a used Keysight boatanchor is something for you ?Further questions:- Dynamic range required- Power level required

author: mayor
author_rank: Regular Contributor
timestamp: August 03, 2018, 11:38:21 am
content: Crap! Did I type 15khz? 15mhz is what i meant. This is for personal use (to tune pcb antennas only), so the only real criteria besides frequency is a low price. A new tinyvna goes for around 500 bucks canadian, which is as high as I can go.Thanks for taking time to respond.

author: Wolfgang
author_rank: Super Contributor
timestamp: August 03, 2018, 11:56:22 am
content: 15MHz instead of 15kHz makes a big difference. What comes closest and is useful is one of the new spectrum analyzers with built-in VNA option, mostly starting from a few MHz. Personally I have seen a Rohde & Schwarz (FPC1500) and a Siglent. The Rohde can go up to 3GHz, and I liked it because its a well designed instrument. The Siglent (at Ham Radio fair at Feriedrichshafen, Germany in June) was still very new and quite buggy at the time, but a lot cheaper than the Rohde. RIGOL has no VNA to my knowledge.Unfortunately, I have never seen something useful for 500CN$ (~400€).If reflection is all you want to measure you could go for a spectrum analyzer with return loss bridge. I have a RIGOL DSA815TG, and it works fine (up to 1.5GHz).There are budget spectrum analyzer based solutions from many manufacturers up to 3GHz (Rigol, Siglent, ...).Tough decision. If its only antenna matching and if you have no spectrum analyzer yet maybe its time to get one anyway.

author: mayor
author_rank: Regular Contributor
timestamp: August 03, 2018, 05:33:51 pm
content: Hi Wolfgang, I dunno if VSWR is really enough? My intent is to use the VNA to find correct values for a pi network just before the antenna. As I understand it, I really need to take phase into account to find the correct values for L and C (I'm new at RF, so all my "knowledge" is to be questioned at this stage!), and using a Smith chart was the "easiest" way to go. This is really home gamer stuff we're talking about here. It may be that I am even overthinking it and that even mismatched antennas will be good enough for my home purposes (using TI's CC1350/1352). Still, using a device that can produce Smith charts sounds like a great learning experience.

author: Wolfgang
author_rank: Super Contributor
timestamp: August 03, 2018, 05:45:09 pm
content: Of course a "real" VNA is a big help for tuning filters or antennas, and a Smith diagram is the representation that helps you most. All pros do it this way.On the other hand, you need to measure phase and not only amplitude, so no way around a "real" VNA. A spectrum analyzer with tracking generator and return loss bridge is a compromise, but could work for homebrew stuff if you know what you are doing.There is another issue: Antennas are one-port devices, so there simple "Antenna Analyzers" that just do S11. Filters and active devices are another story, you need both S11 and S21, a full VNA so to say. Below a few k€ its hard to find something reasonable, and dont forget a cal kit and good cables you will also need.Homebrewing a VNA in the 3GHz range needs a lot of expertise, precision mechanics, expensive RF components and a park of T&M equipment (VNA, SPA, Generators, ...),so I would just forget that.Sorry for no better news.

author: mayor
author_rank: Regular Contributor
timestamp: August 03, 2018, 06:52:39 pm
content: Hi Wolfgang, thanks once more for taking the time. Yeah, you can kind of tell just from the pricing of the lab equipment that high-frequency RF is not so much of a home gamer thing :-) Fortunately, the chances of my project actually leaving the confines of home are low. Thus, I think I can get away with a cheap device like the tiny VNA. What I think I can hope for is to make the match marginally better with such a tool, and have some learning fun doing it.Some people report success with it, so I figure it can't be a completely fruitless endeavour.At this stage: still WTB a tiny VNA, or _maybe_ a pocketVNA if I abandon some of my NFC ideas!

author: Wolfgang
author_rank: Super Contributor
timestamp: August 03, 2018, 10:54:28 pm
content: Any old way, good luck ! Please tell about your experiences with the MiniVNA ...

author: mayor
author_rank: Regular Contributor
timestamp: October 05, 2018, 12:14:44 am
content: @wolfgang, I ended up buyin the xavna (https://www.kickstarter.com/projects/1759352588/xavna-a-full-featured-low-cost-two-port-vna,https://github.com/xaxaxa-dev/vna), which offers good performance! I'm very happy with it so far, and I really like the fact that it's open-source.I had to give up on lower frequency measurements, but that'll be a problem for later. So far, the xavna allowed me to match my first pcb antenna circuit well (though my antenna has limited bandwidth, I think it will work out fine). See attached...

author: Wolfgang
author_rank: Super Contributor
timestamp: October 05, 2018, 12:34:11 am
content: Hi, so you got something going, congrats !I am stuck at the other end of spectrum at the moment, measuring power supply impedances using a VNA (E5061B-3L5).This one goes down to 5Hz and up to 3GHz. Nice, but not cheap.Have fun !