Misfitting RF connectors

[blueskull]

Hi RF gurus,

I have just got my first VNA, and I'm looking for doing some tests with it.

I'm mainly interested in inductance/capacitance measurement and EMI chamber/antenna calibration (actual high sensitivity EMI measurements will be done with an SA).

My VNA came with 3.5mm female connectors, and I'm supposed to mate with a 2.92mm or 3.5mm male connector.

However, those cables are not cheap, and mostly only come in conformable or semi-rigid. I was not able to find a <$100 flexible cable assembly.

So my question is, what kind of damage and performance degradation am I looking at if I rape the connector with standard SMA cables?

My intended frequency is <6.5GHz (VNA limit).

Thanks.

[TheSteve]

Buy some decent quality SMA connector savers, installed them once and never take them off. Everything will work great and you prevent any real wear to the golden 3.5mm connectors. Signal integrity will be just fine.

[richnormand]

What he said ^^

On most of the RF connectors of that type that see regular use I put properly torqued extenders. This has save me a couple of times when using dodgy cheap connectors. Worst were BNC and SMA from ebay. If it seises or jam it is then possible to remove the extended and the jammed connector to get brutal without fear of damage to the instrument. Never had issues with the expensive ones.

I also found that a SMA torque wrench was great to ensure good connections and signal integrity on the VNA in particular.

[Andrey_irk]

The main thing I would be worried about with cheap cables is their stability. It'll limit your calibration accuracy. On the other hand lossy, but stable assembly can be calibrated out and will only degrade the maximum power you can get from your VNA.

Have a look at the Copper Mountain's website. They have some quite cheap but quality gear.
https://coppermountaintech.com/

[radar_macgyver]

BTW, if anyone can suggest a good place to order custom made cables? Cables on demand is very limited on their RF cable selection. Pasternack is stupidly expensive. So far, the only acceptable places I've found are Mini Circuit (limited selection, not-so-cheap price) and Online cables (which its new version of web UI doesn't work, it stuck at PayPal page).

I've used Cross RF, they're a bit cheaper than Online Cables.

[bb37]

I've been using Field Components https://fieldcomponents.com/ for RG400 jumper cables to use inside repeater cabinets (VHF and UHF). I just priced a 3 foot N male to N male at both Cross and Field. Field is about 8 bucks (U.S.) less expensive.

The cables I've gotten from Field in the past seem to be well made and use Harbor Industries cable.

[virtualparticles]

The cables sold on the Copper Mountain Technologies website are really very good. I was impressed when I did some testing in our lab. There is very minimal amplitude and phase variance when moving the cables around after calibration. Bad cables don't actually calibrate out. The phase changes during movement can cause large ripples in the measurement as the calibration is seeing a different phase shift.

[OwO]

Bad cables don't actually calibrate out. The phase changes during movement can cause large ripples in the measurement as the calibration is seeing a different phase shift.

This is true, the consumer grade cables from aliexpress show significant phase error when flexed.
However I have personally tested 3 samples of this cable: https://www.mouser.com/ProductDetail/Johnson-Cinch-Connectivity-Solutions/415-0033-018?qs=%2Fha2pyFadugLAkmyjV6nGzyH5%252BO9qHHc2CQJcSivnSmi7bz%252B847wYA%3D%3D
And they all show excellent phase stability. The S11 error change is below -50dB with significant flexing.

No need for >$100 VNA cables, at <10GHz at least.

[German_EE]

I have heard good things said about the cables from Minicircuits.

[rfdave#gmail.com]

Koaxis has been my goto recently for RF cables. Quick service and their cables are gluten free 

https://koaxis.com/mercury-free/54-quality-and-compliance/60-quality-compliance