OWON Oscilloscopes

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 Post subject: SDS8302 bandwidth
PostPosted: Mon Jan 14, 2013 11:13 pm 
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Joined: Wed May 16, 2012 7:54 am
Posts: 187
Just quick test...

Measured SDS8302V freq BW.
Using 300mVpp signal. Signal source HP8644B
Cable: N-male 1meter M17/084 cable BNC-male + Tektronix 011-0049-011 50ohm feed thru terminator. (Oscilloscope input is around 10pF 1Mohm. (1) so matching is not at all perfect there isn higher frequencies.)

(1) This individual oscilloscope calibration certificate document: CH1 and CH2 input measured values = 9pF and 0.99Mohm

1 Channel in use and 10k memory, 2.5GSa/s
V/Div 50mV
1MHz as reference level 300mVpp
50MHz 298mVpp
100MHz 300mVpp
150MHz 296mVpp
185MHz 312mVpp (highest)
200MHz 306mVpp
220MHz 294mVpp
250MHz 300mVpp
270MHz 276mVpp
300MHz 246mVpp
340MHz 216mVpp -3dB
420MHz 150mVpp -6dB



675MHz 82mV trig just barely
Just for fun:
Changed to 20mV/div (signal still same level)
710MHz 75mVpp -12dB
720MHz 72mV trig but need adjust
750MHz 53mV trig but need adjust, signal still looks nice.
765MHz 44mV trig difficult but just can find trig by adjusting
770...780MHz trig extremely difficult but still can find trig
>780MHz game over.
changed to 10mV/div
More and more vertical wobbling (Nyquist is 1250MHz)
800MHz 32mVpp still trig
830MHz 22mVpp trig but need adjust carefully
860MHz 17mVpp difficult trig but just barely
changed to 5mV/div
950MHz signal can look and trig but have high amount vertical wobbling.


Note: Oscilloscope trig freq counter stop in this test somewhere around 450MHz

Later risetime test with TEK284 70ps risetime pulser.


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 Post subject: Re: SDS8302 bandwidth
PostPosted: Tue Jan 15, 2013 7:01 pm 
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Joined: Wed May 16, 2012 7:54 am
Posts: 187
Nousuajaksi saan noin 1.1ns kun yksi kanava käytössä ja 50mV/div.
Ja tietenkin siis reaaliaikainen 2.5GSa/s "single shot".
Kun tuosta ajaa keskiarvoa se liikkuu noin 1.12ns arvossa.

Signaali tulee Tektronix 284 pulssgeneraattorista joka speksiensä mukaan tuottaa reilut 200mV korkeaa pulssia jossa nousevan reunan nousuaika <=70ps.
Kytkentä sama kuin edellisessä viestissä.

Mutta mikä signaalin laatu on kapelin päässä oskilloskoopin sisäänmeoliittimessä - en tiedä.

Jos käytössä on kaksi kanavaa yhtaikaa putoaa samplenopeus 1.25GSa/s ja nyt keskiarvona nousuaika näyttää 1.16ns.

Ilman keskiarvoistusta ilmenee aliasta eli "corner wobbling" jonkun verran tällaisella signaalilla kun kaksi kanavaa on käytössä

Yksi kanava käytössä tuota ei ole havaittavissa.
Ei siis ole mikään vika tai heikkous vaan ihan "matemaattinen tosiasia" josta herra Nyquist tiesi paljon enemmän.

Ensin kuva jossa yksi kanava käytössä 2.5GSa/s
Toisessa kaksi, 1.25GSa/s
Persistence on kummassakin päällä jotta se kerää vaihteluita näyttölle ja sen takia viiva on tuollainen aika paksu..

Tekin pulssigeneraattori tuottaa nopeanoususita pulssia noin 50kHz taajuudella.
Triggaus skoopissa on varsin vakaa! Eipä se tuossa nanosekunnin ruudussa juurikaan pixeliä enempää vaakasuunnassa pompi.

Kuviin lipsahti kokolailla reippaasti pakkausta joten ovat hiuka suttuisia.
High level packaging reduce picture quality.



Image

One channel in use = 2.5GSa/s
not visible aliasing. Note, trace is thick becouse persistence on for colled example trigger jitter and corners wobbling (one form of aliasing)


Image

Two channels in use = 1.25GSa/s


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