Author Topic: EEVblog #311 - Jim Williams Pulser Followup  (Read 19023 times)

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Offline RRobot

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Re: EEVblog #311 - Jim Williams Pulser Followup
« Reply #25 on: July 15, 2012, 09:00:48 pm »
With regards to the problem you had with the 2 nS vs 3 nS expected rise time on the Rigol, would this have to do with the 1GSa/ps limit on the Rigol introducing up to 1 nS of error? Was this with real or equivalent time sampling turned on?
« Last Edit: July 15, 2012, 09:10:57 pm by RRobot »
 

Offline tinhead

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Re: EEVblog #311 - Jim Williams Pulser Followup
« Reply #26 on: July 15, 2012, 09:34:18 pm »
With regards to the problem you had with the 2 nS vs 3 nS expected rise time on the Rigol, would this have to do with the 1GSa/ps limit on the Rigol introducing up to 1 nS of error? Was this with real or equivalent time sampling turned on?

the error on Rigol E is probably coming from the DSO internal attenuator. While testing the bw with Marconi RF generator
the internal attenuator was off (200mv/DIV), but while testing the bw with pulse generator the attenuator was on (2V/DIV).

From my experience by default all DSO having this particular frontend (Rigol E, ATTEN, Siglent, Tekway/Hantek, etc.)
are calibrated to overshoot a bit while the internal attenuator is enabled, this helps out with the large signals response.

Due this overshoot the resulting bw (calculated back from rise time) seems to be "higher", which of course is not the real case.
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Offline RRobot

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Re: EEVblog #311 - Jim Williams Pulser Followup
« Reply #27 on: July 15, 2012, 09:54:47 pm »
With regards to the problem you had with the 2 nS vs 3 nS expected rise time on the Rigol, would this have to do with the 1GSa/ps limit on the Rigol introducing up to 1 nS of error? Was this with real or equivalent time sampling turned on?

the error on Rigol E is probably coming from the DSO internal attenuator. While testing the bw with Marconi RF generator
the internal attenuator was off (200mv/DIV), but while testing the bw with pulse generator the attenuator was on (2V/DIV).

From my experience by default all DSO having this particular frontend (Rigol E, ATTEN, Siglent, Tekway/Hantek, etc.)
are calibrated to overshoot a bit while the internal attenuator is enabled, this helps out with the large signals response.

Due this overshoot the resulting bw (calculated back from rise time) seems to be "higher", which of course is not the real case.

I would not have thought of that. It would be interesting then to see the results with a 20dB attenuator and 200mV/dv settings.
 

Offline jpb

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Re: EEVblog #311 - Jim Williams Pulser Followup
« Reply #28 on: July 16, 2012, 08:48:18 am »
With regards to the problem you had with the 2 nS vs 3 nS expected rise time on the Rigol, would this have to do with the 1GSa/ps limit on the Rigol introducing up to 1 nS of error? Was this with real or equivalent time sampling turned on?

The error shouldn't be as much as 1nsec in that for a rise time of 2.5 nsecs there should be either 2 or 3 samples on the slope but it will definitely increase the likely error. Another difference might be the interpolation - Agilent uses sin(x)/x which effectively gives 10 times as many points while the Rigol may just use linear.

On the circuit itself, I'm probably being naive, but to both reduce the magnitude of the pulse and increase the RC time constant to make it longer couldn't you just put say a 1k resistor in series with the 50 ohms? The pulse would then be less than 1V and the decay time constant would be 2nsecs or so. At the risk of damaging the transistor, the capacitor value could be made 5 or 10 pF to increase the time constant further and the pulse should not rise above 5V. Parasitic capacitance or inductance associated with the extra resistance might increase ringing but on the other hand the rest of the circuit would be further isolated from the 50 ohms by an extra 1k. It shouldn't affect the rise time of the pulse (I don't think).
« Last Edit: July 16, 2012, 08:49:58 am by jpb »
 

Offline hobbs

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Re: EEVblog #311 - Jim Williams Pulser Followup
« Reply #29 on: July 16, 2012, 02:30:18 pm »
Nice scope.  Of course, my Tek 11801C sampling scope plus a few nice SD-24 plugins has almost twice the bandwidth, (20 GHz, 17 ps rise time) and I paid $1500 for it on eBay a month or two ago.  The faster plugins can go 50 GHz.  The SD-24 also has a 17-ps TDR pulse generator that I use for _everything_--even driving diode lasers.  (You bias the diode laser to just about threshold, and the 8 mA TDR pulse makes a nice fast optical edge--around 80 ps for garden-variety TO-can diode lasers.)

For repetitive signals, sampling scopes are the bomb. 

Cheers

Phil Hobbs
 

Offline rr100

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Re: EEVblog #311 - Jim Williams Pulser Followup
« Reply #30 on: July 16, 2012, 08:21:26 pm »
I just hope you have insurance for all that nice gear stashed around ... wherever you stash it.
 

Offline jpelczar

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Re: EEVblog #311 - Jim Williams Pulser Followup
« Reply #31 on: July 19, 2012, 02:53:57 pm »
Why does the attenuator have series of parallel discs ? I've seen some of the Nokia videos, where they measure something in 4G BTS, and they also used the attenuators withc discs.
 

Offline Rufus

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Re: EEVblog #311 - Jim Williams Pulser Followup
« Reply #32 on: July 19, 2012, 02:59:53 pm »
Why does the attenuator have series of parallel discs ? I've seen some of the Nokia videos, where they measure something in 4G BTS, and they also used the attenuators withc discs.

It is a high power attenuator and the 'discs' are heat sink fins.
 

Offline phenol

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Re: EEVblog #311 - Jim Williams Pulser Followup
« Reply #33 on: January 07, 2014, 10:41:40 am »
 :palm:  I know that this topic is antique, but still....i find that pulser with the associated boost circuit rather intriguing so i thought i should give it a try.

I made the booster with the well known and ubiquitous MC34063 chip and a super tiny handwound flyback transformer. It delivers regulated 95V and operates anywhere from 3 to 12-15V. The entire setup draws around 7mA tops.

The pulser itself is a BFR93A transistor retrofitted on some microwave Agilent demo board so that i could use the 50ohm microstrip lines already present there. The storage cap is 0805 2.7pF.

The two images show the spectrum picked up with a special E near field probe directly on the output microstrip line, the end of which is terminated with 2x 100ohm resistors. The pronounced notches in one of the scans are caused by the 30-40cm coax stub soldered across the storage 2.7p cap. the other scan is the plain circuit itself, no coax.

bye
 


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