Hints about a cheap RF Network Analyzer ? - Page 1
Forum section: electronics / general

author: asilva10
author_rank: Contributor
timestamp: December 14, 2013, 02:26:15 am
content: Hints about a cheap RF Network Analyzer ? Basically, a 2-port (T/R) VNA is fine for me.Anything, portable or for bench, up to 2.4GHz. 2 or 4 ports. <US$1,000The main purposes are 2: 1) antenna impedance, antenna matching circuitry verification and 2) measurements of dielectric properties of materials.Thanks!

author: G0HZU
author_rank: Super Contributor
timestamp: December 15, 2013, 01:29:08 pm
content: You need to be a bit more specific in your requirements... Do you want a vector network analyser or a scalar network analyser?Assuming you want a vector network analyser then your choice is limited if you want something from HP or Anritsu etc.Possible contenders are the HP8714B/C or the HP8753A as these 20-25yr old VNAs both cover up to 3GHz.But you will have to be very patient if you want to find one for around $1k. It is possible to get them for this price but it's also possible to pay 3 or 4 times this price if you want one quickly and you buy from a reputable RF test equipment dealer.Both of the above VNAs are T/R VNAs and not full 2 port VNAs. If you want a full 2 port VNA from HP/Agilent etc then you are looking at $4000 minimum for something like an HP8753C/D.A T/R VNA can only measure S11 and S21 and any one time. If you want S22 and S12 you have to swap the connections to the device under test around or you can use it with an external switching box from HP to get all 4 s parameter measurements.

author: hagster
author_rank: Frequent Contributor
timestamp: December 15, 2013, 07:04:02 pm
content: The USB kit from copper mountain technology is really good.http://www.coppermountaintech.comOnly used the Vector Reflectometer but it's a great bit of kit for most jobs.

author: KJDS
author_rank: Super Contributor
timestamp: December 15, 2013, 07:40:37 pm
content: Quote from: hagster on December 15, 2013, 07:04:02 pmI've just had a look at their data sheets, and they claim 0.1dB through path accuracy for a gain of +5dB thought to a loss of 50dB. That's a remarkably accurate claim. Given that they also state that they have a power measurement resolution of 0.05dB, that gives 0.05dB for log uncertainty, cal errors, temperature and time drift and Whilst these could be excellent, given the stated raw test port and directiivity isn't good, I'm left feeling that they are not being entirely honest, which is a shame as I'm sure it's a useful product, but i far prefer to know the truth.Here's the data sheet for Agilents most advanced PNA series which is about as accurate as it gets. Page 10 shows performance that is 0.07 over a similar dynamic range.http://cp.literature.agilent.com/litweb/pdf/N5221-90001.pdfHowever the 523 series PNA, which is still outside the budget of many companies is worst at about 0.15dB over that dynamic range.http://cp.literature.agilent.com/litweb/pdf/N5235-90004.pdf

author: asilva10
author_rank: Contributor
timestamp: December 15, 2013, 07:56:47 pm
content: The products fromhttp://www.coppermountaintech.comimho are pretty expensive considering other companies and features.

author: hagster
author_rank: Frequent Contributor
timestamp: December 15, 2013, 10:17:24 pm
content: @KJDS remember that accuracy and resolution are 2 different things. It's almost impossible to have a measurement setup that lets you achieve the kind of accuracies that Agilent quote anyway.I agree with the OP that they are not bargain basement prices, but it is professional quality kit and the small size makes them really useful , especially if you have to work away from your lab.Others to look at are the miniVNA and ELAD.http://www.wimo.de/instrumentation_e.html

author: KJDS
author_rank: Super Contributor
timestamp: December 15, 2013, 11:04:08 pm
content: Quote from: hagster on December 15, 2013, 10:17:24 pmI'm well aware of the difference between accuracy and resolution, which is why I'm annoyed at accuracy being claimed that is barely better than resolution. All I ask from any datasheet is that it is clear and accurate. The moment one item is obviously unlikely it casts a doubt over everything else.

author: KD0CAC John
author_rank: Frequent Contributor
timestamp: December 16, 2013, 12:15:22 am
content: I recently picked up one these many for ham radio use , I wish went to 5 Ghz to check wifi also .http://miniradiosolutions.com/minivnapro

author: G0HZU
author_rank: Super Contributor
timestamp: December 16, 2013, 12:23:40 am
content: If we are all looking at the 1300MHz VNA from Coppermountain then I think the 0.05dB power resolution spec refers to the 'setting' resolution of the test source power level. However, the specs for the VNA aren't presented in a way I'm used to seeing and this makes it hard to be certain what the specs really mean...Obviously, they can't realistically meet the overall 0.1dB spec for transmission error without some form of correction on the source match because it has a fairly modest 18dB match and it is just a TR VNA so it can't correct for load mismatch errors. So as KJDS says, there isn't much margin left for other error sources.So I think the TR1300 transmission accuracy spec of 0.1dB is (optimistically?) based on the following:1/They are performing a SOL source mismatch correction in order to reduce source match uncertainty.2/The load port match has >= 28dB return loss and this is fairly good for a 1300MHz VNA.3/There will presumably be errors due to drift/temperature/tracking and noise but I think they have used a very narrow RBW to minimise some of this and presumably the tracking will be excellent with this type of VNA.4/They have probably ignored errors in the external connections and calibration kit.5/The device under test has S11 and S22 that each has a mag of zero.Even so, a transmission accuracy spec of 0.1dB over a 50dB range does seem 'impressive' for a low cost TR VNA. A classic full two 2 port VNA with 12 term error correction can improve on this up to 1300MHz but most TR VNAs that work up to a few GHz struggle to better 0.5dB transmission accuracy because of the issues with source and load mismatch uncertainty.For example, I have an HP8714B 3GHz TR VNA here and I have to pad the ports with precision (£££) attenuators to get low uncertainty on transmission measurements and this sacrifices dynamic range. One day I hope to upgrade it to a full two port HP8753ES (6GHz)

author: steve_w
author_rank: Regular Contributor
timestamp: January 01, 2014, 09:03:59 am
content: you could build your own, check this out. I just started construction.http://scottyspectrumanalyzer.com/msaslim.htmlregardsSteve W

author: woodchips
author_rank: Frequent Contributor
timestamp: January 05, 2014, 10:36:19 am
content: Could always splash out on a vector voltmeter? A network analyser without all the fancy display stuff, does the same job though. Best thing is that they don't seem to be too popular now, so are cheap, and easier to repair.Can't see the problem with accuracy being barely better than resolution. Resolution simply states the smallest change that is detectable, might or might not be accurate. Accuracy would normally be 2 to 3 times larger than resolution. Along with repeatability and precision they are the four measures of how good any measuring equipment is.

author: Gerard
author_rank: Newbie
timestamp: April 22, 2014, 03:47:44 pm
content: There are a lot of low cost VNA's around lately, most for amateur use, and many of them working fine.However, if you want to measure WiFi, GSM, Bluetooth, etc.. applications, the frequency range these units offer you is not adequate: you'll need to go well up to 3GHz and then VNA's are more expensive like Coppermountain: fine, but a lot of dollars.There is an other VNA on the market, under 3000 euro, that goes up to 4 GHz, which is 2-port, fully bidirectional, seehttp://www.megiq.com. I've tested the unit against a Rohde & Schwarz ZVL, and must say I was impressed: it showed me the same graphs and measurements at a fraction of the costs.