Firewire Cable length - how long is too long?

aaroncomp

aaroncomp

1-20-2009
I'm currently using a 10ft firewire cable to connect my CPU with my Firepod. It's just a tad too short (i.e. 1-2 feet) to connect comfortably. So, I've speculated at purchasing, say, a 15ft cable. At what point should I be concerned about signal degradation/latency with firewire cables? Thanks.
 
People freak out about signal degradation and other crap like that when running longer cables but just look at an office building where they run extremely long cables. Of course there's signal boosters but honestly, changing from 10 to 15 feet of cabling is not going to make one bit of noticable difference.
 
10 feet is considered the 'safe limit'. Anything more than that and you're pushing it. Electricity starts to lose it's integrity at about 10' 2". It gets exponentially worse from that point on. 15' is just asking for trouble.
 
solo.guitar said:
10 feet is considered the 'safe limit'. Anything more than that and you're pushing it. Electricity starts to lose it's integrity at about 10' 2". It gets exponentially worse from that point on. 15' is just asking for trouble.
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Hi,
are u talking about voltage drop therefore Signal/Data level drop at the perscribed distance mentioned? (10 feet 2 inches)?
So with a length of 10' compared to 15'...would that make 'a' difference? Really? Kookey! :rolleyes:
SS
 
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aaroncomp said:
I'm currently using a 10ft firewire cable to connect my CPU with my Firepod. It's just a tad too short (i.e. 1-2 feet) to connect comfortably. So, I've speculated at purchasing, say, a 15ft cable. At what point should I be concerned about signal degradation/latency with firewire cables? Thanks.
Click to expand...

The limit for FireWire signaling is 15 feet without a hub in-between as a repeater. You're probably better slapping on a powered hub and a 5 foot cable on the end, but you definitely don't want to go over 15. The nice thing is that according to the spec, if a device can't talk at 15, it is broken or buggy, AFAIK.

Oh, and the other nice thing is that the FIREPOD is a powered device, so you don't have to worry about voltage drop and powering the device off the bus. Yeah, 15 feet should be safe, but no longer.

That said, if you really need a long run, you can go up to a kilometer with optical cable.

http://www.usbfirewire.com/Parts/rr-fw-600.html

The FireWire engineers I've talked to say that above about a kilometer, the devices start having trouble doing bus arbitration because of the latency. :D
 
solo.guitar said:
10 feet is considered the 'safe limit'. Anything more than that and you're pushing it. Electricity starts to lose it's integrity at about 10' 2". It gets exponentially worse from that point on. 15' is just asking for trouble.
Click to expand...

Please put smileys here.... Voltage drop is a function of cable length, voltage, and diameter. Lower voltage requires a larger cable diameter to propagate the same amount of current at a given distance. As long as the current drain on the other end is low enough, you're okay, ignoring SNR.

FireWire signaling is a balanced line mechanism, which gives it excellent noise rejection, so that's largely moot. It's 1vpp, which is the same as a video signal. The farthest I ever ran a video signal (unamplified) over coax was over 150 feet. That 10 foot two inch thing is complete B.S.

The spec says 4.5 meters (about 14.75 feet, but most manufacturers call them "15 foot" cables). Beyond that, the devices will refuse to talk. I think the surface reason for this is that the bias voltage drops below the minimum threshold and the PHYs see the ports as empty. Whether the devices would behave if you provided an external bias voltage on the line or not, I have no idea.

Either way, if a FW device can't talk at "15 feet" (with a decent cable), something is wrong.
 
superspit said:
Hi,
were are u talking about voltage drop therefore Signal/Data level drop at the perscribed distance mentioned? (10 feet 2 inches)?
So with a length of 10' compared to 15'...would that make 'a' difference? Really? Kookey! :rolleyes:
SS
Click to expand...

So zany :p
 
dgatwood said:
Please put smileys here.... Voltage drop is a function of cable length, voltage, and diameter. Lower voltage requires a larger cable diameter to propagate the same amount of current at a given distance. As long as the current drain on the other end is low enough, you're okay, ignoring SNR.

FireWire signaling is a balanced line mechanism, which gives it excellent noise rejection, so that's largely moot. It's 1vpp, which is the same as a video signal. The farthest I ever ran a video signal (unamplified) over coax was over 150 feet. That 10 foot two inch thing is complete B.S.

The spec says 4.5 meters (about 14.75 feet, but most manufacturers call them "15 foot" cables). Beyond that, the devices will refuse to talk. I think the surface reason for this is that the bias voltage drops below the minimum threshold and the PHYs see the ports as empty. Whether the devices would behave if you provided an external bias voltage on the line or not, I have no idea.

Either way, if a FW device can't talk at "15 feet" (with a decent cable), something is wrong.
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I wasn't being serious, I apologize if someone took me seriously.

I've run other cables much longer than 15ft...monitor cables, PS/2, USB, etc. I guess firewire is different?
 
solo.guitar said:
I wasn't being serious, I apologize if someone took me seriously.

I've run other cables much longer than 15ft...monitor cables, PS/2, USB, etc. I guess firewire is different?
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Well... the spec requires that all devices work at 15. Beyond that, there are no guarantees. I've had zero luck with FW hard drives even showing up at 30 feet, but there are people who send video signals several times that far over FireWire. It depends on both the computer and the device signaling loudly enough and being sensitive enough in their decoding hardware....
 
dementedchord said:
the spec as i read it says 4.5 meters as stated earlier... but if i'm not mistaken that works out to 18ft...
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According to Google:

4.5 meters = 14.7637795 feet

So... just shy of 15.
 
Here's all the info on Firewire:

http://en.wikipedia.org/wiki/Firewire

"Cable length is limited to 4.5 metres (about 15 feet), although up to 16 cables can be daisy chained using active repeaters, external hubs, or internal hubs often present in FireWire equipment. The maximum cable length for any configuration is limited to 72 meters in the S400 standard."
 
Okay, so I had already placed my order before more replies were made advising I stay at the 4.5 meters or below. Well, the cable I ordered was actually 10m - yeah, pretty long. It just came in and is working perfectly so far. I've recorded a few tracks and no stutter or increased latency noticed yet. Strangely, it has added this analog-like warmth to my tracks (yes, I jest). I'll update this post if anything changes.

The brand is Unibrain - purchased it off of Buy.com.
http://www.buy.com/prod/10M_1394FIR..._98_00_ME_NT_UNIBRAIN/q/loc/101/10319305.html

Here is a link to the companies take on the cables and how they "exceed the 4.5m cable length"
http://www.unibrain.com/Products/p1394/cables_a.htm
 
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