# Speed of fathom tethere without tether interface **URL:** \ **Category:** Cables\ **Created:** [May 30, 2025, 10:51am UTC](https://discuss.bluerobotics.com/t/speed-of-fathom-tethere-without-tether-interface/20507 "2025-05-30T10:51:27Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![SmokeySalmon](https://avatars.discourse-cdn.com/v4/letter/s/b3f665/32.png) [@SmokeySalmon](https://discuss.bluerobotics.com/u/SmokeySalmon)\ **Post date:** [May 30, 2025, 10:51am UTC](https://discuss.bluerobotics.com/t/speed-of-fathom-tethere-without-tether-interface/20507/1 "2025-05-30T10:51:27Z")
Hi, i’m currently building an underwater ROV, and i’m planning to use around 40m of **fathom tether** to connect the blue robotic’s **ethernet switch** inside the ROV the to the laptop. Since the **fathom-X interface** board are for long distance communication, can this setup work without the fathom-X interface, with just two rj45 connector at the ends? If so, what bandwidth can I expect to get with this setup? I would really appreciate any insights on this, thanks! ---
**Author:** ![tony-white](https://sea1.discourse-cdn.com/flex019/user_avatar/discuss.bluerobotics.com/tony-white/32/18385_2.png) [@tony-white](https://discuss.bluerobotics.com/u/tony-white)\ **Post date:** [May 30, 2025, 4:04pm UTC](https://discuss.bluerobotics.com/t/speed-of-fathom-tethere-without-tether-interface/20507/2 "2025-05-30T16:04:33Z")
Hi @SmokeySalmon - Welcome to the forums! Because Fathom tether does not meet the cat-5 specification, a link at that distance using two twisted pairs and regular ethernet communications is _not_ likely to succeed! Stranded wire is used for flexibility, instead of solid-core… The Fathom-X tether interface will provide ~70-80 Mbps over just a single twisted pair without issue! I’d recommend trying regular ethernet, and if you have connection reliability / bandwidth issues, installing the tether adapters. ---
**Author:** ![SmokeySalmon](https://avatars.discourse-cdn.com/v4/letter/s/b3f665/32.png) [@SmokeySalmon](https://discuss.bluerobotics.com/u/SmokeySalmon)\ **Post date:** [May 31, 2025, 4:40am UTC](https://discuss.bluerobotics.com/t/speed-of-fathom-tethere-without-tether-interface/20507/3 "2025-05-31T04:40:09Z")
Thank you for your reply! In this case I’ll try a regular ethernet cable _without_ the interface first. But I’m also planning to use the **Blue robotics ethernet switch** to communicate with two microcontrollers over the tether and the **Fathom spool** for organisation. Then from what I’ve gathered, the ethernet switch uses only two twisted pairs inside the tether, and the spool has a slip ring core with binder 770 connectors. Would any of these features affect the bandwidth over a regular ethernet cable? ---
**Author:** ![tony-white](https://sea1.discourse-cdn.com/flex019/user_avatar/discuss.bluerobotics.com/tony-white/32/18385_2.png) [@tony-white](https://discuss.bluerobotics.com/u/tony-white)\ **Post date:** [May 31, 2025, 7:02am UTC](https://discuss.bluerobotics.com/t/speed-of-fathom-tethere-without-tether-interface/20507/4 "2025-05-31T07:02:45Z")
Hi @SmokeySalmon - You should be fine with a 40m cat5 or cat6 cable going from the ethernet switch to a topside ethernet connection, going through the slip ring and binder connector - maybe not to a full 100mbit, but likely very close! ---
**Author:** ![SmokeySalmon](https://avatars.discourse-cdn.com/v4/letter/s/b3f665/32.png) [@SmokeySalmon](https://discuss.bluerobotics.com/u/SmokeySalmon)\ **Post date:** [June 1, 2025, 3:06am UTC](https://discuss.bluerobotics.com/t/speed-of-fathom-tethere-without-tether-interface/20507/5 "2025-06-01T03:06:42Z")
Great! Thanks for you help : )