Ceramic 2.4GHz antenna

What models were they? i have a pile of dead hard drives, and I believe there are several IBM . I know I saw a dead 15 GB IBM EIDE drive the other day.

--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

Not to mention punched card sorting machines, and made those damned school clocks that jumped omce a second while you were trying to concentrate. :(

--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

"Michael A. Terrell" wrote in news: snipped-for-privacy@earthlink.net:

I think the 15 GB one was one of those that went bad in bulk. That said, it was the 15 GB platters, the really notorious drive was the 75 GXP, they put

5 15 GB platters in it. Hitachi only recently dared to try 5 with the 400 GB drives. Those are ok though, I have two, with no problems at all. One on backup offline, the other running all day, switched off for most nights, and not the slightest complaint for several months so far.

There's a lot of smoke around that 'Deathstar' issue, but I managed to ignore it, Hitachi had bought the line soon after, and changed things. If your drives are from IBM's GXP75 range, they are probably afflicted, but if they're from the Hitachi era, they almost certainly died of natural causes, or violence.

I've had 9 Deskstars, and two died directly resulting from bad handling by me, while moving hardware in a couple of very frustrating sessions. Caused by problems that were not of those drive's making. Another was bought secondhand, it has a controller problem that I never understood, probably got zapped slightly by the previous owner. It won't co-operate with any mainboard I have, but is currently doing very well in a FireWire enclosure which it gets on well with. None of the other 6 ever dropped a byte unless the OS crashed and borked something. Two of them are old 40 GB drives.

Long post, I know, but there is so much shouting and panic on the net about these drives, that if the subject comes up, I have to counter it. Even if I brought up the subject myself. :)

I Sold and installed hundreds of the ibm drives with the "nic" "deathstars" all had a cooling fan and the number of failures was tiny , considering where I trade and how hot it is makes me wonder about the reality of the claims about them

why 50 Ohms?

see:

or Goggle "why 50 ohms"

Also I have a question for the op...why do you want to BUY a ceramic antenna when at these frequencies a small antenna can be printed directly on the PWB for free....

Mark ,

Um... I happen to be using a chipset that has the same name as the comics... email me privately.

Cheers

PeteS

Because a ceramic antenna can be done in a smaller space than the PCB equivalent (I have indeed already done that for the GSM/GPRS unit) and it can also be multipolarised, which is difficult with an ordinary PCB antenna.

There *can* be reasons to buy these things ;)

Cheers

PeteS

from:

, about 2/3 way down the page:

"Why 50 ohm coax ? Standard coaxial line impedance for r.f. power transmission in the U.S. is almost exclusively 50 ohms. Why this value was chosen is given in a paper presented by _Bird Electronic Corp._ Standard coaxial line impedance for r.f. power transmission in the U.S. is almost exclusively 50 ohms. Why this value was chosen is given in a paper presented by Bird Electronic Corp.

Different impedance values are optimum for different parameters. Maximum power-carrying capability occurs at a diameter ratio of 1.65 corresponding to 30-ohms impedance. Optimum diameter ratio for voltage breakdown is 2.7 corresponding to 60-ohms impedance (incidentally, the standard impedance in many European countries).

Power carrying capacity on breakdown ignores current density which is high at low impedances such as 30 ohms. Attenuation due to conductor losses alone is almost 50% higher at that impedance than at the minimum attenuation impedance of 77 ohms (diameter ratio 3.6). This ratio, however, is limited to only one half maximum power of a 30-ohm line.

In the early days, microwave power was hard to come by and lines could not be taxed to capacity. Therefore low attenuation was the overriding factor leading to the selection of 77 (or 75) ohms as a standard. This resulted in hardware of certain fixed dimensions. When low-loss dielectric materials made the flexible line practical, the line dimensions remained unchanged to permit mating with existing equipment.

The dielectric constant of polyethylene is 2.3. Impedance of a 77-ohm air line is reduced to 51 ohms when filled with polyethylene. Fifty-one ohms is still in use today though the standard for precision is 50 ohms.

The attenuation is minimum at 77 ohms; the breakdown voltage is maximum at 60 ohms and the power-carrying capacity is maximum at 30 ohms.

Another thing which might have lead to 50 ohm coax is that if you take a reasonable sized center conductor and put a insulator around that and then put a shield around that and choose all the dimensions so that they are convenient and mechanically look good, then the impedance will come out at about 50 ohms. In order to raise the impedance, the center conductor's diameter needs to be tiny with respect to the overall cable's size. And in order to lower the impedance, the thickness of the insulation between the inner conductor and the shield must be made very thin. Since almost any coax that *looks* good for mechanical reasons just happens to come out at close to 50 ohms anyway, there was a natural tendency for standardization at exactly 50 ohms."

------------------------------------------------------------------------

Hope This Helps! Rich

I think 52 ohms is the impedance at the bottom of a 1/4 wave whip with a proper ground plane, or something like that.

Cheers! Rich

...and 90ohm tried and coax inside the systems. There was a mix though, some was 50ohm (mainly clocks, IIRC). The higher impedance reduced power (and delta-I). Lower impedance is faster (higher current to charge the load capacitance). They also used high-speed dielectric (basically GoreTex).

--
  Keith

Great technology and did exactly what was intended. Marketing was another issue though. Do remember that IBM was about to circle the drain in the early '90s. There was no money to promote OS/2, even if M$' contract allowed it.

--
  Keith

I have a 75GXP (one of the supposedly bad ones) that's still going strong. I have a 37GXP also, still spinning.

--
  Keith

Probalbly (nothing to do with...). It's 377ohms, IIRC. Of course there is 600ohm ladder-line (differential ;-).

--
  Keith

Nominally 52 , however bending the radials down produces a near perfect match which depending on construction can often be 43 ohms or lower impedance and the bending alters things for match but of course being coax the feed is quite unbalanced . ( and a matched arial may not be resonant)

There was a rumor that the IBM drives were failing because of the glue of a QA sticker in the interior. Something that wasn't tested by engineering. Anyone knwo of this is true?

That said I've taken apart a few 4 and 9 GB SCSI drives. One had a head cash and you could see the glass of the platter. Nice. Another gave me a big surprise when I opened it: the top platter had two crosses written on it with a black marker. That side obviously did not have a head, and manufacturing selected platters for this single-sided kind of use. But I still feel the use of a black marker in a 'clean room' like this is odd.

Thomas

There are no 'bad brands' I think, but bad batches. Like the controller chips with bad epoxy causing a bunch of failures.

Once researched how a drive failed (tried to fix it), and it was the spindle motor having a partial short. That drive (Seagate Medalist) had layer of foam plastic on the outside of the PCB with a thin metal plate over it. Sill, it wasn't the electronics that overheated - or would the electronics have failed first, blowing up the motor, which then blew up the swapped in board?

Thomas

Zak wrote in news:456369f0$0$13907$ snipped-for-privacy@news.tweakdsl.nl:

False. There's a duct formed between the two plates in the upper shell, the breathe hole is there, it's the only way in unless you remove the screws, and there's no sticker over it, there must NOT be one, for obvious reasons. Even if there was, there's no way a small amount of resilient adhesive is going to go right through along that duct after managing to pass a porous membrane. Not even silicone grease can creep that well.

I've looked inside one of the Deskstars I broke with bad handling. No stickers inside, nor any in any other brand of drive I've had. They'd never risk leaving that much risk of contaminants inside where the platters and heads are.