Ethernet and LWDAQ Cables

[Kevan Hashemi]

A customer writes:

I was recently involved in upgrading the system and installing PoE microseven cameras and moving a currently unused octal/LWDAQ driver/attena set up into an existing faraday to up the number of recording slots.

Something caught my eye when I was looking on your website. Specifically here:

https://www.opensourceinstruments.com/E ... 7/SCT.html

and here:

http://www.bndhep.net/Electronics/LWDAQ ... t%20Cables

and it is on the use of ethernet cables and LWDAQ cables.

Am I right in thinking that from the back of the LWDAQ driver to the Octal it should be a specific LWDAQ cable. Firstly, are these available for purchase and if so can you quote me for 5 of these?

The second question i have is about ethernet cables to that allow power and data transfer to/from the cameras. We currently have shielded cat6 ethernet cables going from the switch to the ethernet block outside the canopy. Shielded cat 5e cables are contact the ports on the inside and connect to the camera. I note on your website that it says that ethernet can/should be unshielded outside the canopy. Is there a problem with running shielded ones?

[Kevan Hashemi]

Dear Nat,

I am going to answer your question in detail, because it is a good question, and I feel that a short answer will be more confusing than a long answer.

> Am I right in thinking that from the back of the LWDAQ driver to the Octal it should be a specific LWDAQ cable.

In your question, you are implying that the cable from the LWDAQ Driver (black box) to the Octal Data Receiver (silver box) connects to the "back" side of the driver. In our documentation, the "back" side of the driver has one RJ-45 socket, one power plug, and one switch. The "front" side is the one with eight RJ-45 sockets, thirteen LED indicators, and one switch. Here is a picture of the front side:



The cable from the receiver plugs into one of the eight sockets on the front of the driver, usually socket No1, closest to the LEDs. This cable functions as a "LWDAQ root cable". If the cable is longer than ten meters, the cable needs to be a "LWDAQ Cable", or else the communication between the driver and receiver will be unreliable.

Network cables contain eight wires. The wires terminate at either end with an eight-way modular connector. All modern network cables, and all LWDAQ Cables, are "straight-through", meaning that pin 1 on one end is connected to pin 1 on the other end, the same for pin 2 on both ends, and so on.

To the first approximation, LWDAQ and Ethernet cables are the same. Provided the cables are short, this approximation is good enough. Inside the cable, however, the eight wires are twisted into four pairs. Twisted pairs are good for transmitting high-frequency logic signals over long distances. In Ethernet cables, the pairs are 1/2, 3/6, 4/5, 7/8. In LWDAQ Cables, they are 1/2, 3/4, 5/6, 7/8.

When I chose the pinout for the LWDAQ connector back in 2003, I made a mistake. I thought I was picking the same pinout as Ethernet, but I was wrong. By the time I realized my mistake, it was too late to fix it.

The LWDAQ uses 3/4 to download data from the receiver to the driver. In a LWDAQ cable, 3/4 are twisted together, so they can go a long way without distortion. With a solid-wire LWDAQ cable, you can read out your receiver from 130 m away. Hence the name "Long-Wire DAQ". With an Ethernet cable, the communication will be reliable only up to ten meters.

In your system, ten meters is more than long enough. You can use a short Ethernet cable to connect your driver to your receiver. And of course you can use an Ethernet cable to connect your driver to the Ethernet.

> Firstly, are these available for purchase and if so can you quote me for 5 of these?

As you can see: buy network cables from your local cable supplier and they will be fine.

> The second question i have is about ethernet cables to that allow power and data transfer to/from the cameras.
> We currently have shielded cat6 ethernet cables going from the switch to the ethernet block outside the canopy.
> Shielded cat 5e cables are contact the ports on the inside and connect to the camera.

I believe you have Ethernet Feedthroughs on the floor of your Faraday Canopy, like this:



You have your Power over Ethernet (PoE) switch outside the canopy and you are running Ethernet cables from the switch to the feedthrough, and from the other side of the feedthrough to the cameras inside the enclosure. Please correct me if I'm wrong.

> I note on your website that it says that ethernet can/should be unshielded outside the canopy.
> Is there a problem with running shielded ones?

The cables from the switch to the feedthrough can be shielded or unshielded. Depending upon how the cameras are designed, it is possible for shielded cables between the switch and the feedthrough to cause problems with PoE startup. But we have tested three types of MicroSeven camera so far, and none of them show any startup problems with shielded cables. So you can use shielded everywhere if you want to. The cables inside the enclosure must, however, be shielded, in order to permit telemetry reception.

> Thanks in advance for your response

I hope I answered your questions. If not, please register on this forum and ask again.

Best Wishes, Kevan