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!

  • 1
    \$\begingroup\$ 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... \$\endgroup\$
    – user76844
    Nov 20, 2017 at 8:07
  • \$\begingroup\$ 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. \$\endgroup\$
    – ahogen
    Nov 20, 2017 at 8:15
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    \$\begingroup\$ 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? \$\endgroup\$
    – dim
    Feb 9, 2019 at 8:27

1 Answer 1


I understand the basic difference between 100Base-T and 100Base-TX ...

Are you sure? Maybe between 10BASE-T (original Ethernet) and 100BASE-TX (Fast Ethernet)? Or between 1000BASE-T (Gigabit Ethernet) and 100BASE-TX?

Both 10BASE-T and 100BASE-TX work over two twisted pairs at once. While 1000BASE-T works over four pairs at once.

Making it shorter, people often write simply but mistakenly 10/100BASE-TX or 10/100BASE-T instead of proper 10BASE-T/100BASE-TX or 10BASE-Te/100BASE-TX to indicate that a MagJack support both (original and Fast) protocols.


  • On the Digikey page you referred to, there is no difference between selects in the Application field, select both and choose between all the will-be-shown possibilities;
  • On the Mouser page, there is no "simple" way to filter out only Fast ones.

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