[Mike Peel]

I currently have a PowerBook G4 15" 1.25GHz (as described here. I've just started work at a radio telescope, and they ban certain CPU frequencies because it interferes with the measurements made on the telescope. My CPU frequency is within the banned range, so I currently can't use my laptop there. They've suggested that I use the laptop with the processor performance in "reduced" mode, but they need to know the frequency it operates on before they say that it's OK to use. I can't seem to find out where this CPU frequency is listed - does anyone know for definite what it will be, or can point me to somewhere that will say? Thanks in advance.

[jpg71]

According to some PB15 G4 Developer Notes I found, the 1.25ghz model clocks down to 765 MHz in "Reduced" performance mode.

15-inch PowerBook G4 Developer Note: System Software

I'm surprised that the telescope is that sensitive - I guess FCC Class B devices aren't shielded enough for that application?

[ibook_steve]

That's the most ridiculous thing I've ever heard. All laptops, including Powerbooks, are shielded to prevent what you are talking about. And even so, the emissions from a laptop are extremely low and would not affect anything. Does this mean that for the past few years, nobody has been able to use a new computer at your facility because all new computers were in this "banned" frequency range? Whatever. In any case, in reduced mode, the frequency is halved.

Steve

[Mike Peel]

Thanks for the information.

Bear in mind that this is one of the biggest radio telescopes on the planet (Jodrell Bank), and is heavily used for scientific research. I'll quote from the information we were given:

"In order to minimise the amount of RFI generated by electronic equipment, items in use must be shielded or run at suitable clock speeds to avoid the main observing bands. This includes all computers including user owned laptops."

Apparently there were problems a few years back where they bought a set of 700MHz computers, and a research team observed them at 1.4GHz - it interfered with measurements of the 21cm line (a very important frequency in radio astronomy). They had to turn off all of the computers while observing, and ended up buying RF shielding boxes for them.

Computers with frequencies between 1.8 and 2.2GHz (among others) are allowed, so I guess I'll be shopping for a new laptop in the very near future. Fingers crossed that the new MacBook Pro's come out next tuesday or so...

[mduell]

Originally Posted by ibook_steve

That's the most ridiculous thing I've ever heard. All laptops, including Powerbooks, are shielded to prevent what you are talking about. And even so, the emissions from a laptop are extremely low and would not affect anything. Does this mean that for the past few years, nobody has been able to use a new computer at your facility because all new computers were in this "banned" frequency range? Whatever. In any case, in reduced mode, the frequency is halved.

That's the most ridiculous post I've seen. I don't think you appreciate how sensitive research caliber radiotelescopes are or how the inverse cubed law works.

[ibook_steve]

No, I do appreciate it. It's ridiculous because if this was the case, then nobody could purchase any new computers during the years when that speed range was the main frequency on new computers. I doubt they stopped buying computers because the pace of technology reached the point where it affected the telescope.

Steve

[mduell]

Originally Posted by ibook_steve

No, I do appreciate it. It's ridiculous because if this was the case, then nobody could purchase any new computers during the years when that speed range was the main frequency on new computers. I doubt they stopped buying computers because the pace of technology reached the point where it affected the telescope.

I guess you missed Mike Peel's post (emphasis mine):

Originally Posted by Mike Peel

Apparently there were problems a few years back where they bought a set of 700MHz computers, and a research team observed them at 1.4GHz - it interfered with measurements of the 21cm line (a very important frequency in radio astronomy). They had to turn off all of the computers while observing, and ended up buying RF shielding boxes for them.

[imitchellg5]

My 867MHz becomes 400MHz.

[Kyros]

So can I assume my 1.5 ghz 12 inch reduces to 766 or so?

[Leonard]

It never hurts to be over-cautious with expensive sensitive material. You would think they would buy some sort of detector/measurement device that could accurately measure the CPU speed or emissions from the laptops. Maybe there isn't one, though. I wouldn't depend on a Tech/Developer Note.