I needed to connect two buildings and was having machines in to dig a 4’ (1.2m) deep trench between them for a water line so I went to Amazon and bought a 250’ (76m) pre-terminated copper Cat6 cable. As I was going to be burying it I wanted to be sure it worked, so I used it as a “fly lead” for my laptop for a week or two first and it worked fine. I know it initially connected at 1Gbps, but (stupidly) I can’t be 100% certain it stayed at full speed the whole time.

Now that it’s buried I’m only getting 100Mbit/s. It does sometimes connect at 1Gbit/s, but it later falls back to 100Mbit/s. I have an old Cisco SG300-10P on one end and a Ubiquiti Edge Router X on the other. I disabled 802.3 Energy Efficient Ethernet (EEE) on the Cisco and, as expected, it made no difference. The Cisco has built in cable test capability and it says I have an 84m open cable on all pairs - even when connected to the ER/X and working. Is there some sort of loopback/test termination I can make for the other end to get a better (more meaningful) result? I’ve tried searching, but failed.

The plug at one end did get pushed through some silicone caulk as it was being shoved through a hole in a wall. I cleaned it off with alcohol and it looks clean, but I’m considering cutting the plug off and replacing it with a socket as my next debugging step as it would be more convenient anyway.

I live about an hour from the nearest large town so there’s no way I’m getting someone here with a proper tester at a reasonable price. If I can’t figure it out myself I’ll revert to the pair of airMax GigaBeam radios that have given me a solid 800Mbit/s for the last 3 years with only visual alignment!

Edit: this is the cable https://a.co/d/i6mYLy1

  • notgoldEnglish
    3·
    3 days ago

    Unplug both ends and use a multimeter to check resistance between the individual wires at one end. Should be OL (out of limits) on screen.

    Try earthing one end as slazer2au said. The cable may be bringing in stray voltage thats messing with the device.

    84m for pairs sounds right on a 76m cable when you adjust for the twists.

    Some devices can push distance better than others. The cisco has eee and a short range option from memory. Make sure you turn all off on the port in question.

    Try the link with a pair of laptops.

    Cut off the connectors and determinate.