# Correct Ethernet Jack + Magnetics for 100Base-TX

I've been shopping around for Ethernet jacks for use in a personal project. The part specifically states that it's internal PHYs are 100BASE-TX/10BASE-T/Te IEEE 802.3

I understand the basic difference between 100Base-T and 100Base-TX, but I guess I don't understand why an Ethernet jack and/or the magnetics need to be spec'd for this. It's all getting clocked through the wire at ~125MHz, right?

Digikey seems to differentiate between -TX and -T. Mouser's parametric search doesn't mention anything like the connection speed and is very unhelpful, showing me stuff with and without magnetics.

The 100Base-TX jacks with mags seem to be more expensive than -T (on Digikey) so that leads me to believe some timing requirement of 100Base-TX require entirely different magnetics specs or something. But if it doesn't matter, I certainly don't want to spend $4 on a jack when I could spend only$1.60.

Any advice? I'd appreciate it!

• for $1 you need a chinese supplier (look up for AICO). Western companies, even Wurth, will cost you$2-4. On the other hand, talking to them is much easier, you will get samples quickly...
– user76844
Nov 20 '17 at 8:07
• I was referring to the cheapest option shown by Digikey at the above link. It's a J1B1211CCD from WIZnet. Thanks for the tip. I'll check out AICO and Wurth. Nov 20 '17 at 8:15
• The question shouldn't be whether to get a 100baseT vs 100baseTX jack. Almost all implementations are TX anyway. You should select the jack+magnetics to use based on what your specific PHY chip asks for, because they have different requirements. Which PHY chip are you using?
– dim
Feb 9 '19 at 8:27