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| Cheap triax connector ? |
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| (*steve*):
--- Quote from: alm on June 17, 2017, 05:15:05 am ---You sure you got that model right? Pomona 5299 is a 3 lug triax (male) to BNC (female) adapter with shield shorted to guard (not good for anything with an active guard like a SMU). --- End quote --- I'm well aware of the triax to BNC converters and I blame <insert favouite blame thing here> for totally failing to spot this, even though I looked up the spec sheet. |O Oh well, I can use it for my Keithley 600B. I already have a converter to BNC but my regular coax to alligator clip cable has a resistance of 50G\$\Omega\$. I can probably use this to allow me to connect my nice Keithley triax cables And I guess I'll be filing off that damn lug after all. Thanks everyone for the heads-up. :-+ |
| ebclr:
https://item.taobao.com/item.htm?spm=a1z10.3-c.w4002-2384871945.56.29ed68dexQhfcl&id=536567327738 |
| TerraHertz:
I've been looking for affordable triaxial BNC connectors (and cable) for a while. I have a HP 4140B pico-amp meter I need to connect to a test fixture, and it's required to use triaxial 3-lug BNCs and cable. The triaxial cable is Belden 9222. Low leakage, low microphony. Suitable connectors are Pomona model number: 5218. See: https://www.pomonaelectronics.com/products/connectors/bnc-triaxial-m-3-lug-belden-9222-triaxial-cable BNC Triaxial (M), 3 Lug For Belden 9222 Triaxial Cable But these cost around AU $78 each, and the first price break is at Qty 25. Still not much cheaper. Too rich for me. Anyway, I finally found an affordable source on Aliexpress. Store name: Chengtec Store Triaxial BNC male connector, domestic high quality, JY75-1.5 / JY75-2 / JY75-3 1553B cable Curently AU$ $23.98 each (15.19 USD), 10% off for 5 or more. I'd originally ordered just two. They arrived recently and are well made and fit Belden 9222 cable perfectly. The construction allows for re-using them if you need to replace the cable. A big relief to me, since they are still quite expensive. Insulating material seems to be PTFE, so hopefully they are suitable for the pA meter. It appears the store only recently listed these connectors, and I was their first buyer. Perhaps they'll lower the price if they start getting significant sales numbers? Here are some pics I took of one I received. Incidentally I also found an ebay seller (wzjworld) with some used Belden 9222 for sale. That cable is OK too, and cheap. |
| noreply:
Just be careful with 'ebay' or Amazon - as you usually get what you pay for. I got some 50 ohm BNC inline terminators from Amazon - these were VERY reasonably priced - but compared to an original Rigol part - which is 5 times more expensive - their quality was reflective of the cost. I know the Triax connector is not same as what I am referring to - but the concept of an alternative 'cheaper' item stays same. The Rigol BNC is a machined part - expensive to make - the 'Amazon' BNC is cast metal -poor tolerances - much cheaper to make - not to mention the Rigol termination resistance is spot-on 50.0 ohms, the 'Amazon' part is 49.8 ohms. Remember you tent to get what you pay for. Good luck in your selection :) |
| TerraHertz:
All good points, and thus why out of caution I initially only bought two of these 'cheap' triax connectors. Also why I posted photos of them here, to show that they are not the cheap diecast zinc alloy rubbish that does exist. These are machined brass, nicely plated, seem to be close-tolerance parts. Whether the 'gold' plating is actually gold, and what's the plating thickness, don't know. As for impedance matching, for the frequencies involved in the target system (all under 15MHz) that isn't going to be a significant issue. Down in the pico-amp measurements range a far more significant factor will be surface and bulk conductance of the insulating materials. But if those are half-way decent (teflon/PTFE) a fingerprint on the insulator surface would swamp the material characteristics anyway. |
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