Aircraft Grade Ethernet Cable?

[SteinAir]

No problem just using plain old "cheap" M27500 shielded mil spec wire in twisted pairs (2 conductor). We may stock some ethernet some day, but for the time being haven't yet found a big need for it.

Cheers,
Stein

[sparkcrafter]

Thanks for the feedback.

I'm only doing one run between the GTN and the remote transponder, so I hate to spend $300 on a special order.

I did finally locate a source for the wire at aerotronics.com for $3.65/ft, but I'm tempted to use Stein's suggestion and use 2-conductor M27500.

JasonM: Some of the newer Garmin transponders use an ethernet connection between the GTN and the transponder.

-Jerald

[g3xpert]

Originally Posted by sparkcrafter

Thanks for the feedback.

I'm only doing one run between the GTN and the remote transponder, so I hate to spend $300 on a special order.

I did finally locate a source for the wire at aerotronics.com for $3.65/ft, but I'm tempted to use Stein's suggestion and use 2-conductor M27500.

JasonM: Some of the newer Garmin transponders use an ethernet connection between the GTN and the transponder.

-Jerald

Hello Jerald,

We were guessing the GTN to GTX link is what you are wiring. We did a test using two standard MIL-C-27500 22 AWG twisted, shielded pair cables (one on the two Tx wires and one on the two Rx wires), that was 15 ft. long, and it worked fine.

We are revising our installation guidance to indicate that you may use Mil-C-27500 twisted, shielded pair wire if two separately shielded pairs are used.



We may eventually get comfortable using 4 wire MIL-C-27500 shielded cable, but for now we prefer that two wire twisted pair cable like shown above is used since that was tested.

Thanks,
Steve

[cardmarc]

Originally Posted by g3xpert

Hello Jerald,

We were guessing the GTN to GTX link is what you are wiring. We did a test using two standard MIL-C-27500 22 AWG twisted, shielded pair cables (one on the two Tx wires and one on the two Rx wires), that was 15 ft. long, and it worked fine.

We are revising our installation guidance to indicate that you may use Mil-C-27500 twisted, shielded pair wire if two separately shielded pairs are used.



We may eventually get comfortable using 4 wire MIL-C-27500 shielded cable, but for now we prefer that two wire twisted pair cable like shown above is used since that was tested.

Thanks,
Steve

Interesting that the Ethernet 10424 cable Garmin specifies does not have each pair individually shielded. The pairs are just twisted together. Foil and shield over all 4 wires. Wonder if it makes a difference?

[fl-mike]

The pair twisting is more important than individual shields on the pairs. An overall shield (or individual shielded pairs) will keep the EMI in. So, use an overall shielded avionics grade Enet cable, or two pairs of shielded 27500 (one for the TX pair, and one for the RX pair). Now, for the short distances we are using, you probably could get away with 4-cond shielded 27500, but there is going to be some crosstalk and signal degradation. You'll note that regular old Cat5 cable uses twisted pairs with different twist rates to reduce crosstalk from pair-to-pair.

The problem with Ethernet (100Mbps or gigE) is that the symbol frequency is 125MHz, right smack dab in the middle of the comm band. A never-ending source of EMI grief for avionics using Enet.

[lr172]

Originally Posted by fl-mike

The pair twisting is more important than individual shields on the pairs. An overall shield (or individual shielded pairs) will keep the EMI in. So, use an overall shielded avionics grade Enet cable, or two pairs of shielded 27500 (one for the TX pair, and one for the RX pair). Now, for the short distances we are using, you probably could get away with 4-cond shielded 27500, but there is going to be some crosstalk and signal degradation. You'll note that regular old Cat5 cable uses twisted pairs with different twist rates to reduce crosstalk from pair-to-pair.

The problem with Ethernet (100Mbps or gigE) is that the symbol frequency is 125MHz, right smack dab in the middle of the comm band. A never-ending source of EMI grief for avionics using Enet.

+1
This is why I wouldn't use 4 cond tefzel wire. That is NOT twisted pair wire. All four wires are twisted in bulk, which is about comparable to untwisted wire for the issues related to cross talk on ethernet lines. For demanding high speed applications, each pair must be twisted indiviually before being bundled together. I have found unshielded twisted pair aviation cable, but can't remember the number. It is for arinc applications, which call for twisted pair without the need for shielding, similar to ethernet.

Larry

[JDA_BTR]

I used two of the 2- wire shielded cable to make this connection between a 650 and 45R transducer. No error good data in all regimes. Experimental type rating. Prob need the correct cable for long runs or certificated ships.

[1001001]

Originally Posted by lr172

+1
This is why I wouldn't use 4 cond tefzel wire. That is NOT twisted pair wire. All four wires are twisted in bulk, which is about comparable to untwisted wire for the issues related to cross talk on ethernet lines. For demanding high speed applications, each pair must be twisted indiviually before being bundled together. I have found unshielded twisted pair aviation cable, but can't remember the number. It is for arinc applications, which call for twisted pair without the need for shielding, similar to ethernet.

Larry

The twist rate (turns/length) is important too, is it not?

[lr172]

Originally Posted by 1001001

The twist rate (turns/length) is important too, is it not?

Sorry, but that advancement came after I left the industry, which was just around the time that the Cat 5 standard came out. I suspect that you are correct. That level of intervention was not required with the 25-50 MB transmission rates, but wouldn't be surprised to learn that it was for the 100+ MB transmission level that the Cat 5 was designed for.

I know that the twist rate was always specified and therefore important to eliminating cross talk. It stands to reason that using different twist rates on the pairs would change the performance and therefore potentially better reject cross talk.

Be advised that Cat 5 is pretty much the standard today and is specified for many less demanding applications. Therefore, not all of the properties of the Cat 5 standard are required in all applications. I would speculate tha the avionics gear is not using the 100 MB transmission rates. Slower speeds are less sensitive and therefore generally more robust.

Larry