Teardown: DirecTV Ethernet over coax adapter

[NiHaoMike]

I read that those DirecTV Ethernet over coax adapters (DECA) can be used standalone. I looked up the price on Amazon and to my surprise, a bulk pack of 24 adapters was only $30. That translates into $1.25 per adapter or less than 1/4 the cost of implementing Wifi over coax using cheap USB Wifi adapters. That price even includes an 18" Cat5 patch cable and a 6" high quality coax patch cable per adapter. No power supply included however, since in their intended application, the IP set top boxes they're used with supply the power. A common 12V wall wart or piggybacking off any 12-18V supply (but see caveat later) works nicely for standalone use.

The adapters are very well made, but what surprises me is that they bothered to include a rather massive overvoltage protection tube. Even more interesting is that there's an ICS542 clock divider, which on further reverse engineering appears to be used to clock some of the DC/DC converters. I'm going to guess that they're doing that in order to keep the noise on the analog rails predictable and easy to null out.

Hint: if you want to open one of those adapters, pry it apart on the same side as the two coax connectors. The other side is very close to some SMD components that are likely to be damaged if you try to pry it from that side.

As for using and hacking them, the main disadvantage is that they're very slow to boot, taking a few minutes before the link comes up. Not sure if they're waiting for a signal from the master node (then timing out and going into P2P mode) or if they're just slow to boot by design. Keep that in mind if you're thinking about just powering them from the 12V rail inside a PC or other switched supply. A quick test seems to indicate that they perform about as well as plain 100Mb Ethernet over a random long piece of coax (50' or so) I had lying around. Not sure how well they deal with noisy lines (will test later), but I'm expecting much less than Homeplug or Wifi since coax is usually a very clean medium.

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Nicely made.  These might be common enough to find replacement firmware that would connect quicker.

J4 looks like it could be a serial port.

Is 12V supplied on the coax, or somewhere else?

Thanks for posting this!

[NiHaoMike]

12V is supplied on the coax next to the Ethernet port. There's also a passthrough for high frequency RF signals (guessing 700MHz and above since the adapter works on somewhere between 500-600MHz), which could be helpful if you also want to run Wifi over coax on the same cable.

A little more reverse engineering reveals that they put in a soft start circuit to minimize the inrush. Also interesting is that the first buck converter outputs 8V but it only seems to be used for supplying the other buck converters. Apply 5V there and it seems to run just fine, although the power LED will not light as it's supplied from a voltage threshold circuit. It's certainly the most overengineered cheap gadget I have ever reverse engineered.