advice on buying second-hand network analyzer [title edited] - Page 1
Forum section: electronics / rf-microwave

author: bug13
author_rank: Regular Contributor
timestamp: April 29, 2017, 02:47:06 am
content: Hi guysI want to get more hand on, and learn about more about antenna matching and tuning, so I need a VNA. New ones are too expensive for me, so I want to get my hand on asecond one.second-hand one. (didn't know why I typed second one, doh!!)I see this on ebay:Keysight Agilent HP 8711C 300 kHz to 1.3 GHzhttp://www.ebay.com/itm/Keysight-Ag...530939?hash=item28223416fb:g:6toAAOSwYIxX~jTQcorrect link:http://www.ebay.com/itm/Keysight-Agilent-HP-8711C-300-kHz-to-1-3-GHz-Network-Analyzer-30-Day-Warranty-/172372530939What do you guys think? I would love you hear your advice/suggestion before parting my money.Cheers.James

author: KD0CAC John
author_rank: Frequent Contributor
timestamp: April 29, 2017, 02:13:03 pm
content: You need to double check your link , it does go to eBay - but no results ?There is other options that can be new and cost less than either $500 or $1,000 , many are tied to using a computer to use .For that range , one is the miniVNA Tinyhttp://miniradiosolutions.com/54-2/I have had the miniVNA Pro for some yrs. , not as high in frequency coverage .

author: Teuobk
author_rank: Contributor
timestamp: April 29, 2017, 09:41:55 pm
content: Are you maybe linking to this one?http://www.ebay.com/itm/Keysight-Agilent-HP-8711C-300-kHz-to-1-3-GHz-Network-Analyzer-30-Day-Warranty-/172372530939If so, a few thoughts:That's a 75 ohm input impedance model, so if you want to use it to characterize 50 ohm devices you'll need a "minimum loss pad"The HP 8710 series of VNAs provides decent performance. Not super-high performance, but totally fine for most things you'd want.That one has a T/R test set, so if you want to do full S-parameter measurements, you'll need to do some cable swappingThe full CLIP (schematics, etc.) for the 8711C is available, so if something were to break, you'd have a good shot of diagnosing and fixing itI have a 8714ES, and I've been very happy with it (after I repaired it).

author: bug13
author_rank: Regular Contributor
timestamp: April 30, 2017, 12:13:34 am
content: Hi John,miniVNA look interesting, I think it may be better suit for me, thanks for the info. PS: the link is fixed.

author: bug13
author_rank: Regular Contributor
timestamp: April 30, 2017, 12:16:17 am
content: Hi TeuobkI think the 75Ohm impedance really turn me off, all the stuff I am interested in are 50Ohm, thanks for pointing this out, it helps me a lot. Thanks for your replay!!

author: BigBoss
author_rank: Regular Contributor
timestamp: May 16, 2017, 12:43:41 am
content: It's not a VNA, it's just a Scalar Network Analyzer.You cannot measure impedances in complex form on the Smith Chart.That's why it's very cheap..

author: Teuobk
author_rank: Contributor
timestamp: May 16, 2017, 05:09:34 am
content: Quote from: BigBoss on May 16, 2017, 12:43:41 amInteresting. I checked the datasheet, and you're correct: the 8711C is a scalar network analyzer. The 8712 and 8714 are proper vector network analyzers, with Smith charts, complex impedance, etc., so I had assumed the whole 8710 series were VNAs -- nope! Good to know.

author: bozidarms
author_rank: Regular Contributor
timestamp: May 16, 2017, 10:15:11 am
content: Hi,give a try to - 1.3 GHz DG8SAQ Vector Network Analyzer VNWA3E -,it is more than adequate.Regards

author: BigBoss
author_rank: Regular Contributor
timestamp: May 16, 2017, 02:59:20 pm
content: Quote from: Teuobk on May 16, 2017, 05:09:34 amIf you can find old stuff 8720C, it's really good VNA ( I used for years) but it may be a bit pricey.

author: KJDS
author_rank: Super Contributor
timestamp: May 16, 2017, 05:16:40 pm
content: Quote from: Teuobk on May 16, 2017, 05:09:34 amThe 8711C and the 8713 are vector network analyzers, however they only displays scalar information. It is possible to suck the vector info from the GPIB port.

author: TheSteve
author_rank: Unknown
timestamp: May 16, 2017, 07:49:27 pm
content: You can also convert the 8711x series to a 8712x with a small firmware change to a socketed chip.

author: BigBoss
author_rank: Regular Contributor
timestamp: May 17, 2017, 04:58:56 pm
content: Quote from: KJDS on May 16, 2017, 05:16:40 pmIf it's so why this equipment does not show the vector information on the screen??? I don't think that is so easy.Vector information is more complicated than scalar one.The equipment should measure "the Phase" that is more complex.

author: KJDS
author_rank: Super Contributor
timestamp: May 17, 2017, 05:34:06 pm
content: Quote from: BigBoss on May 17, 2017, 04:58:56 pmYou'll have to ask Keysight why it doesn't show the phase data on the screen.

author: TheSteve
author_rank: Unknown
timestamp: May 17, 2017, 07:59:37 pm
content: 8711/8712 are the same hardware just as 8713/8714 are. The display of vector information was simply disabled on screen on the cheaper models. As was already stated it has always been available via the GPIB port. Or a change to the internal eeprom will upgrade an 8711 to a 8712 or an 8713 to a 8714. With the upgrade all vector information is available on screen.

author: hendorog
author_rank: Super Contributor
timestamp: May 17, 2017, 08:10:04 pm
content: FWIW I made an offer a while back of $430 on that auction. Seller never came back to me.

author: chrisl
author_rank: Regular Contributor
timestamp: May 18, 2017, 04:12:36 am
content: Quote from: BigBoss on May 17, 2017, 04:58:56 pmLooks like this is very doable... no idea how.http://minolta1.cninet.cz/HP8712C/