VNA Testport Cable - Page 1
Forum section: electronics / rf-microwave

author: EVlab
author_rank: Contributor
timestamp: July 21, 2017, 07:33:16 am
content: Hi all!I'm searching for some testport cables (N connectors, 18GHz) for my VNA. As it is for hobby use, I can not afford the professional VNA testport cables, so I'm looking for alternatives.Taking a look at Pasternack webpage, I found a VNA ruggedized test cable (PE3VNA1803-24). As price is quiet high (length 48in = 730USD), I thought about other cables like PE302-48 = 160USD (higher losses) or PE330-48 = 308USD (low loss).As I have no experience in this topic, I would like to know what to look out for in case of budged is a concern (hobby use)? Is loss and phase stability that important? Is ruggedness very important? Thereby I mean "important" is handle it gently, not moving a lot around, no moving setup. All in focus of hobby use -> good measurements with acceptable costsFurthermore I would be pleased to get any hint for a product if someone has undergone the same trajectory already.Best, Simon

author: rx8pilot
author_rank: Super Contributor
timestamp: July 21, 2017, 07:53:09 am
content: Joining the conversation.Sent from my horrible mobile....

author: nctnico
author_rank: Super Contributor
timestamp: July 21, 2017, 10:32:07 am
content: AFAIK cable loss isn't that important since you would calibrate that out before taking the measurement. I'd look on Ebay for N cables which use low loss coax. Expect to spend some money though. For example 50cm SMA cables with Huber+suhner RG223 coax cable cost $30 to $40 each from China.

author: tggzzz
author_rank: Super Contributor
timestamp: July 21, 2017, 11:09:12 am
content: High quality cables are often available cheaply at hamfests.Don't forget to consider therepeatabilityof connections!

author: slurry
author_rank: Regular Contributor
timestamp: July 21, 2017, 11:31:20 am
content: For not-so-critical measurements i tend to use RG400 with good quality crimped connectors by Huber Suhner or Rosenberger,Never let any low quality ebay connectors near your expensive test equipment ports!

author: mgberry
author_rank: Newbie
timestamp: July 21, 2017, 04:13:12 pm
content: Ive been down this road and have continued to evaluate options. If your willing to keep the cables stationary post calibration you can save a lot money.I own and have tested Gore VNA cables, new Pasternack cables, used Agilent cables purchased online and cheap RG316 ebay specials. Buyinganyused cables is a gamble. I concluded that I was far better off buying some new test cables from Pasternack for a few hundred bucks than rolling the dice on ebay. These are my everyday bench cables and when things really matter I pull out my Gore cables.Matt

author: D3f1ant
author_rank: Frequent Contributor
timestamp: July 21, 2017, 09:25:48 pm
content: I do dislike crappy cloned connectors (had some eBay N so misformed they wouldn't even screw on) but does the cable really matter that much (or make that much difference) for short 50cm or less lengths on a bench? Looking at youtube videos you see plenty of adapters and things used with what looks like fairly ordinary RG58 and BNC cables. I can understand using semi rigid cables have some advantages in ensuring repeatability. I suppose it does depend on the frequencies involved as well, but like nctnico suggested, arn't cable anomalies normalised out doing calibration with cables? Learning RF stuff is really facinating, can't wait to get a decent VNA and test this all for myself.

author: rx8pilot
author_rank: Super Contributor
timestamp: July 21, 2017, 09:29:54 pm
content: Curious how much the Keysight, R&S cables cost new?

author: rfeecs
author_rank: Frequent Contributor
timestamp: July 21, 2017, 09:42:11 pm
content: A 40GHz Keysight cable, I believe actually made by Gore, is on the order of $5,000.https://www.gore.com/products/gore-vna-microwave-rf-test-assemblies

author: rx8pilot
author_rank: Super Contributor
timestamp: July 21, 2017, 10:04:56 pm
content: Quote from: rfeecs on July 21, 2017, 09:42:11 pmI just fell out of my chair.

author: hendorog
author_rank: Super Contributor
timestamp: July 21, 2017, 10:33:57 pm
content: The cheapest cables (for up to 6GHz) that I found, which looked like reasonable quality, were the used Orange Megaphase cables on eBay.I have three and they look OK to me on the VNA for loss, return loss and stability. However the SMA connectors are not very nice to use as they tend to bind, which is made worse by the rigidity of the cables themselves.I put that down to wear and tear. These cables are not new and also perhaps the connectors were never that great to begin with.e.g. I have one of these, N-SMA 8GHz cables:http://www.ebay.com/itm/Megaphase-TM8-S1NK-60-DC-to-8-GHz-SMA-M-to-Type-N-Hex-Knull-RF-Test-Cable-60/221285280496?_trksid=p2047675.c100005.m1851&_trkparms=aid%3D222007%26algo%3DSIM.MBE%26ao%3D2%26asc%3D41451%26meid%3Dc5db2791811e4da59e1ea3808c4044d3%26pid%3D100005%26rk%3D3%26rkt%3D6%26sd%3D221268869303

author: Bud
author_rank: Super Contributor
timestamp: July 21, 2017, 10:38:23 pm
content: Advice from Dr Joel of KeysightQuoteSource:https://community.keysight.com/message/64590?commentID=64590#comment-64590

author: hendorog
author_rank: Super Contributor
timestamp: July 22, 2017, 12:23:37 am
content: Quote from: Bud on July 21, 2017, 10:38:23 pmJust tried the first test on my 3 cheapo eBay Megaphase cables. The two TM8 (8GHz) cables passed at the metrology grade level, and the third TM4 (4GHz) was at the 'not worth using' level. Of course no way to know whether the TM4 cable is crap or that this particular cable is just knackered.- I set the IF bandwidth to 100Hz which made the variations easier to see by reducing the noise in the trace.

author: darrell
author_rank: Regular Contributor
timestamp: July 22, 2017, 01:07:50 am
content: A few more options:These are very similar to Gore Phaseflex, also some lower cost options:https://www.maurymw.com/store/Cable-Assemblieshttps://www.minicircuits.com/WebStore/Cables.htmlIf you go with something other than a precision test cable, I'd suggest using precision connector savers on the test port end. You don't want to be mating your cal kit with SMA connectors.Edit:I'd also add to avoid used cables. They are effectively a consumable in production test. I retired a set of the $5000 Gore cables at my old job due to them being worn out by flexing.

author: Neganur
author_rank: Unknown
timestamp: July 22, 2017, 09:37:30 am
content: assuming your VNA has N-type and not 3.5mm NMD,I find that using good quality N-to-SMA female adapters + good quality semi-rigid Suhner grade SMA male-to-male cables is acceptable.Good quality SMA male-to-male (or even 3.5mm) is easier and cheaper than poor quality N-ruggedized.

author: mswhin63
author_rank: Frequent Contributor
timestamp: July 22, 2017, 02:55:57 pm
content: >Quote

author: EVlab
author_rank: Contributor
timestamp: July 25, 2017, 12:29:04 pm
content: Thank you very much for you support so far!I find the following recommendations very useful, because they offer an online-shop in contrast to many other "traditional" manufacturers.https://www.maurymw.com/store/Cable-Assemblieshttps://www.minicircuits.com/WebStore/Cables.htmlAre there any other recommendations for testport port cable manufacturers with online-shop for individuals?I find it very disappointing, that many companies don't deliver to individuals and only do business with companies.

author: tggzzz
author_rank: Super Contributor
timestamp: July 25, 2017, 02:32:04 pm
content: Quote from: EVlab on July 25, 2017, 12:29:04 pmI've never worried about that too much.I am forced to take note of companies that don't want to bother with small orders. Such companies often have distributors that deal with small orders. The split between manufacturing/wholesale and retail is easy to understand: the business characteristics and parameters are fundamentally different.