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The Rigol DS1052E
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EEVblog:
That is normal, a 50MHz scope does not stop measuring signals at 50MHz, it's just 3dB down at 50MHz.
Check out the response graph someone posted in another thread, the 50MHz Rigol is only 6dB down at 100MHz, so will still easily display a signal.

The triggering issue?, well, that's just the nature of triggering. Sometime the scope gets it easy, sometimes you need to tweak it.

Dave.
TrentO:
Dave, thanks for the incredibly fast response!

I'm still a little confused about the attenuation levels-- my expectations don't seem to jive with what I'm seeing--

The Rigol and the Tektronix show virtually the same waveform at 66MHz--


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And at 100Mhz--


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It's not until 125Mhz that any sort of difference becomes apparent--


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I didn't take any pictures of the measurements at 25Mhz and 50Mhz, but the small error of margin between the Rigol and the Tektronix remains consistent-- the Rigol reads a little lower on the v/div for any given reading...

I seem to have missed that class on what -dB x means... could you explain?


Someone posted this on the equipment demo-center door, shortly after the executive management team gave me access--

ACHTUNG! Das machine is nicht fur gefingerpoken und mittengrabben.
Ist easy schnappen der springenwerk, blowenfusen und corkenpoppen mit spitzensparken.
Ist nicht fur gewerken by das dummkopfen.
Das rubbernecken sightseeren keepen hands in das pockets.
Relaxen und vatch das blinkenlights!


Also-- you were right about tweaking the triggering-- it took one full turn of the v-position dial to find the waveform, and like turning of the trigger dial for the Tek to finally get it. The Rigol got it automatically, each and every time!

EEVblog:
It's unlikely both scopes will have the same roll-off filter characteristics, so any differences would be normal. There are different types of analog filters and they can have different "orders" (rate or slope of attenuation with frequency).

dB is just a ratio, so instead of saying something is 0.5 times the value of something else, you can say it's "-6dB".
So if one scope reads 1V and the other scope reads 0.5V for the same signal then the say the second scope is "6dB down"

Some good rule of thumb numbers to remember:
3dB up or down is 0.707 (1/sqrt(2)) or 1.414 (sqrt(2))
6dB up or down is a half or two times (6dB=20 * log(0.5))
20dB up or down is 1/10th or 10 times (20dB=20* log(0.1))

And also, adding in dB's is like multiplying. So if something is 40dB down then it's 1/100th. etc
So if someone says something is 1 millionth, or 1ppm, or whatever, you can quickly use the rule of thumb to calculate it's -120dB (i.e. 6 (zeros) x -20dB) instead of using the formula dB=20*log(x)

Engineers like to talk in dB for many things!

Dave.
TrentO:
Hallelujah! Yes! Yes! I SEE THE LIGHT!  (The band!)

at  25 Mhz, I see a ratio of 1.00, rigol/tektronix v-p-p
at  50 Mhz, I see a ratio of .97, rigol/tektronix v-p-p
at  66 Mhz, I see a ratio of .90, rigol/tektronix v-p-p
at 100 Mhz, I see a ratio of .66, rigol/tektronix v-p-p
at 125 Mhz, I see a ratio of .49, rigol/tektronix v-p-p

So my VERY rough, woefully unscientific results using peak-to-peak measurements comparing the two scopes shows a differential of -3dB approaching 100 MHz, and -6dB at 125 MHz. The world makes sense to me again!

Thanks for your help on this one Dave.

-Trent

 
 
Dago:
Btw. tip for TrentO (and others as well): Enable the frequency counter from Utility -> Counter ON, it is much more accurate than the measure -> Freq thing (I believe this measures the frequency from the waveform showing on the screen, but the counter counts it from a longer period).
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