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LOSTCIRCUITS		SHORTCUTS: IDE Cables: Wired RF Transmitters UDMA 33 vs UATA Cables Mechanical and RF Properties Real Cables Real World System Problems Tips and Conclusion Any Comments? Cheetahs and Cudas on the web
ATA Not-So-FAQs    Or: Why Ribbon Cables are unsuitable for RF transmission of data
(Article by snn47, March 17, 2003)          -.. ..-. ..... .--. -.--

Preliminary Conclusions and Possible Cure

Reasons for changes in the propagation impedance, cross-coupling between adjacent signal wires and signal-velocity from one setup to another are :

Impedance of the drive and controller in high/low signal level will be different for different models.
Reflection of signals that garble the pulse, due to incorrect termination impedance or impedance-inconsistencies from the controller to the drive meaning the Impedance from the controller and the drive(s) differ.

If there is a a second drive (connector present/connected) the impedance will fluctuate at this point.

A. Only one HDD per controller channel.
B. Use a cable with only 2 connectors.

-Signal delay will increase with the length of the flat-ribbon-cable propagation of the signals were intended for a max. flat-ribbon-cable length of 18" with ~ 5ns/m would be 2.3ns delay.
C. shorten the cable whenever possible. D. If the case requires long cables consider mounting just the HDD closer to the connectors of the controller or consider exchanging the usual desktop case, for a 19" case. Mount the HDD just above or below the PCB-controller-connector to allow you to reduce the length of the flat-ribbon-cable to a few cm.

Flat-ribbon-cable with different isolation material (higher/lower eR) and change in the conductor diameter will change the ratio of (2D/d).

Are rounded cable used?
E. Try exchanging the cable against another type/brand of flat-ribbon-cable.

Is the flat-ribbon-cable at some point parallel to a conducting grounded surface?
F. Try a different routing of your flat-ribbon-cable away from a ground-plane,

Was the cable cut apart and/or rolled it to get a rounded cable?
G. Unroll it and try B., if cut apart then start with A.

Is the drive mounted in a removable drive rack?
H. Remove HDD from the drive-bay and start with A.

Final Thoughts and Comments

Do you really need optimized performance for more then the boot drive(s if RAID)?

If not then consider adding a IEEE1394-IDE-bridge to a drive which are also known as Firewire or I-Link. It eliminates all this problems and reduces the flat-ribbon-cable to just a few cm. The Firewire cable length can be up to 4,5m (IEEE1394a and 100m for IEEE1394b).

A single IEEE-1394a Firewire-HDD (Oxford-911chip) will give you up to 35MB/s of the theoretical limit of 50MB/s (IEEE1394a and 100MB/S for IEEE1394b), which is more then adequate for all Audio/Video work, and of course for all DVD- and CD-R(W)-drives.

IEEE-1394a Raid configurations will be much faster, but then IEEE-1394b is already part of newer Apple-PC's and should be around for PC soon too.

Firewire will give you Plug & Play, allow access to drives also for additional PC just by moving the cables. If mounted in an external case you can take it away as well.

The only disadvantage of IEEE-1394(-Raid) is the missing boot support in present BIOS, which make SATA-IDE bridges an attractive alternative if your board provides you with an controller.

This is my second draft of my understanding of these problems from an RF-perspective (being a HAM :D ) since today's transfer rates fall into the RF category rather than just AC.

I hope it will start discussion or give us in future some superior products as long as IDE-drives exist. If you use all/part of it all I require is that you leave the references to the work of others and me.

If I made wrong assumptions, didn't have some information you know of/found out or if I made an error please let me know and I'll correct it.

snn47@compuserve.de

References

[1] "Eight Ways To Kill Your HDD", IBM 60GXP vs. Maxtor D740X-6L: http://www.lostcircuits.com/advice/ibm_maxtor/3.shtml

[2] "Pitfalls in Parallelism", Seagate Barracuda SATA V Serial ATA and the 7 Deadly Sins Of Parallel ATA: http://www.lostcircuits.com/advice/sata150/3.shtml

[3] Lars Brenner, Volle Platten Power IDE-RAID-Adapter c't 2003, 1, p.126, Heise Verlag

[4] Working Draft, T13 1153D, Revision 18, 19 August 1998, Information Technology - AT Attachment with Packet Interface Extension (ATA/ATAPI-4)

[5] Working Draft, T13 1321D, Revision 3, 29 February 2000. Information Technology - AT Attachment with Packet Interface - 5 (ATA/ATAPI-5) file name d1321r3.pdf

[6] T13, 1410D, Revision 3b 26, February 2002, Information Technology - AT Attachment with Packet Interface - 6 (ATA/ATAPI-6), d1410r3b.pdf [7] E02119r0, 1.8 inch 3.3V parallel form factor Proposal

[8] Electonics Designer Handbook, Landee, Davis, Albrecht revised by Giacoletto, 2nd edition, chapter 8 transmission lines, McGrawHill

[9] Funktechnische Arbeitsblätter 1 - 11, Dipl.Ing Rudolf Schiffel und IngArthur Köhler, 2.Ed. 1974, Franzis Vlg.

[10] ABIT Hot Rod 66 (UltraDMA/66 Controller Card) Review: http://www.xbitlabs.com/storage/abit-hotrod66.html

[11] ATA/100 Investigation: http://www.xbitlabs.com/storage/ata-100.html

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