Keyboard Shortcuts
ctrl + shift + ? :
Show all keyboard shortcuts
ctrl + g :
Navigate to a group
ctrl + shift + f :
Find
ctrl + / :
Quick actions
esc to dismiss
Likes
- TekScopes
- Messages
Search
|
Re: More fun with avalanche pulsers
True... but if this were the source of the ringing, then wouldn't I see substantially less ringing, and a corner closer to square, on the S-4 25 ps sampling head compared to the S-2 (75) or S-1 (350 ps) heads? The S-4 and S-2 traces look basically identical, and the S-1 looks bandwidth-limited ("softer" corner and ringing) as I expected...
|
|
Re: How to explain how negative feedback lowers noise?
Thank you folks for an interesting and informative discussion.
Clearly, there is not a general consensus regarding whether or not negative feedback reduces noise. There seem to be many who believe that it does. A simple Google search for "negative feedback amplifier advantages" returns these hits on just the first page: Negative feedback also has effects of reducing distortion, noise, sensitivity to external changes as well as improving system bandwidth and input and output impedances." There are some advantages of negative feedback amplifier which are given below, The negative feedback reduces noise. It has highly stabilized gain. It can control step response of amplifier. It has less harmonic distortion. It has less amplitude distortion. It has less phase distortion. Negative feedback has following advantages: ? The negative feedback reduces noise ? It has less frequency distortion means improved frequency response ? Better stabilized voltage gain ? It has less harmonic distortion. The use of negative feedback can discriminate against sources of noise or distortion within an amplifier. ------------------------------------------------- So, in attempting to understand the issue, suppose I have a need for an amplifier with a gain of 20 dB but the device I am using has a greater gain so I build three test circuits.[Lab assignment] For the first circuit, I achieve the gain target by adding negative feedback. For the second circuit, I achieve the gain target by adding input attenuation. For the third circuit, I achieve the gain target by using output attenuation. Each of these circuits will have a noise figure that reflects the difference between a given S/N at the input and the S/N at the output. The circuit with the best noise figure is? |
|
Re: More fun with avalanche pulsers
Chuck Harris
It might just be the math. You cannot get
a perfectly flat top even with infinite bandwidth... Look up Gibbs Phenomena. Basically, the Fourier combination of sine waves to create a square wave will never quite get to a perfect square, because there will be spikes and ringing at the discontinuities.... even if you go out to infinite bandwidth. -Chuck Harris On Sun, 28 Mar 2021 09:23:01 -0700 "Charles" <charlesmorris800@...> wrote: That is true, but Bodnar's pulser is a full order of magnitude faster |
|
Re: More fun with avalanche pulsers
That is true, but Bodnar's pulser is a full order of magnitude faster than mine (30-40 ps vs. 380) and I'm sure nothing is what it seems at that speed.
Anyway, I may just stop here rather than drive myself nuts trying to get a perfect square pulse! It's faster than any of my scopes can measure except the sampler. On my 7A26/7403 (the amp is 200 MHz but the mainframe only 65 MHz) I just see a little 1 volt rounded bump a few ns wide ;) |
|
Re: 492AP screen dump
When Tektronix introduced the 492, it was an advance in technology to offer so much capability in such a small package. The 492P model includes a GPIB interface for remote control.
The 492 platform became the foundation for subsequent models with additional capabilities. The 494 introduced drift free operation with an internal reference, direct keypad entry of frequency and other parameters, and with the 494P, the ability too directly plot the screen contents to an attached plotter.. That capability continued in later models such as the 492AP. Unfortunately, since the 492P came first, it doesn't have the direct plot capability. |
|
Re: 492AP screen dump
Thanks Robert,
I have everything to view the 492P screen plot on PC, but I don't know how to start data transmission from the 492P. I have a Panasonic oscilloscope connected to the PC via the Prologix GP-IB to USB converter and it works fine. I press REC, 1 and START on the oscilloscope front panel and on the PC I get the screen plot as if it were done by the HP plotter. But on the 492P I don't know how to do it. --Cheers Attilio |
|
Re: 492AP screen dump
Hi,
From the KE5FX 7470.EXE manual: "7470.EXE is a Win32-based emulator for the HP 7470A plotter. It will acquire an HP-GL/2 plot and render it in a window. The plot can then be printed, viewed as an overlay with other plots, or saved in several different graphics file formats as well as its original HP-GL/2 format." So the nswer is yes. Note that it is plot though, not a live, changing display. |
|
Re: How to troubleshoot a faulty 7B92A?
Thierry,
See if the Cherry microswitch is is opening and closing. That will do what you describe if it is not mounted right. This is pushed by the pin on the front knobs. The white spool is between the pin and switch. This plastic piece looks like a spool or bobbin used in the underside of the area where the needle goes down into is on a sewing machine. The main time knob that pulls out activates this switch. I have seen this problem before. The two screws that are on the readout board attached to the switch on the small metal plate adjust the switch physically. Check AR like Dan G. said. His advice is the best place to start signal tracing. That AR point is T.P. waveform 8 which shows 6V peaks. This point is the extreme lower left of the board. A 51 ohm resistor is going to that test point. If no signal there, go back to test points in the hexagon numbers to see where you have it. See if TP550 waveform is there. That you can solder a short piece of wire at the base of the TP and bend it out towards the front to access it with a probe. At least the board can stay screwed back on for further testing. Remove the wire after the problem is found. At point AF above P801 should be about .8V peaks according to number 11 waveform on <4> which is also waveform 9 on <5> Are the pulses coming in on pin 1 of U820? It should be about 450mV peaks. I am assuming the contacts on things have been cleaned and known working. If not, clean them. The three switches below the time knobs are frequently dirty being open on the end allowing dirt in. The voltages on the triggering boards can be off. Depending upon the S/N of yours, check the voltages at points were internal adjustments are to see if any are off. Int. DC Bal and/or Sens pots could have been turned by the previous owner. If your S/N is below 70000 then the tunnel diodes are the most likely cause of no triggering. Checking waveforms at the test points 7 on <2> or at pin 1 of U820 (waveform 8) will be a good indication of the tunnel diodes operation. Another thing I have seen is the solder connections of these stiff gold pins not be adequate. It is possible one or more of these need additional solder. The ones that I have seen bad this way are usually the ones where the trace is on one side of the board and the solder for the pin is on the other side of the board. The ones that have this problem, I added a bit of solder at the base connecting it to the trace. This plug-in is one I have seen this on where the logic board is connected to the main board. Check the other transistors that are 3571TP. You will find the Q numbers in the parts list. You may have more leaky ones giving you trouble. R82 and R86 will run rather warm. These are the 510 ohm 1/2 carbons. See if you get the 5.7V on the load side (pins 8 and 9 of U74). These may be high. If your are bad, I suggest using 1W. These are used on S/N 70000 and higher. They are located on the main trigger board between U74 and U122. I hope this has been of some help. If Dan or anyone else has suggestions, help him out. Mark |
|
Re: How to troubleshoot a faulty 7B92A?
thank you Dan/Mark. nearly there...
There was no reference voltage . I've therefore replaced U752 (LM741). This has restored the sweep on the interface board, AV, AU (holdoff) and can now see the sweep on TP450 I still have the 7B92A on the vertical slot and cannot see any sweep I found that Q902 and Q912 were leaky and have replaced both on the output board. I can now see the sweep for the delayed time base but not for the main timebase (ie horizontal line). I can see the sweep at TP450 so not sure where things go wrong on the output board It is not that easy to troubleshoot the output board with the horizontal logic board on top of the interface board Thanks Thierry |
|
Re: More fun with avalanche pulsers
Thanks :) I stuffed it all into the 5 x 2-1/4 square Minibox, including a 6 ns semirigid charge line.
Displayed 10-90 risetime is just under 400 ps on a 75 ps sampling head. Flat-top could be flatter but that really hurts the risetime... I'd need to go to microstrip and leadless (surface-mount) parts to get any more performance. That's another project for another day! Pics added to avalanche pulser album. |
|
Re: 7A16A high frequency compensation.
Hi all,
I've just uploaded two screenshots: /g/TekScopes/photo/262075/4 /g/TekScopes/photo/262075/5 It's my PG506's (+) fast rise output directly coupled to a PM3340 2GHz Philips oscilloscope. High quality, 80 cm RG223/U with Uber-Suhner connectors (BNC to N) cable was used. 10x attenuator was used to keep the PG506's output level over 100 mV. A nice 632 ps rise time with no aberrations. This implies that the calibration of my 7A16A is practically perfect, as Albert also said Cheers, Max |
|
11801, 11801C and CSA803A repair projects
This started as a conversation among @oculus, Jerry Hancock and I. Jerry got an 11801C, @oculus got a CSA803A and I've got a 2nd 11801 which Jerry in a fit of foolishness sold to me ;-) along with an SD-26 with a bad channel that turned out worked perfectly the 2nd time I tested it before shipping it back to Jerry. But it's still causing Jerry trouble. Fortunately, I took photos and can prove it *really* did work correctly in the far left slot of 11801 #1. When I got it and tested it, I wrote on it in pencil, so I know it's the one I got from Jerry and not one of the set of 4x I bought for $$$.
toggle quoted message
Show quoted text
As I was finishing this I realized we really should archive the work on the list. The previous emails don't amount to anything, but at this point it's worth archiving. Have Fun! Reg ----------------------------------------------------------------------------------------------------------------------------------- I've got 11801 #2 on the bench. There is no calibrator output. Interestingly it passes all the diagnostics but they don't seem to run automatically. However, there is a way to jumper those off which I'll need to look up, pull the correct board and check. I just discovered that there are additional diagnostics windows for each of the blocks across the top of the Utility screen which vary with the subsystem selected on the LHS. On 11801 #1 setting the trigger to "internal" starts the calibrator verified using a DSO. But it does not on #2 which explains why I couldn't get autoset to work on #2. IIRC I tried running #2 in the stack in the dining room and got error messages from the diagnostics. The SD-26 I sent back to Jerry, when it came didn't work properly on one channel verified on 11801 #1. Before I sent it back to Jerry I tested it on #1 again and it worked. But Jerry is having problems with it. I have now verified that the calibrator is getting an input signal, but not producing output. I don't yet know if it is getting power. I hope it's not. That <20 ps source would be pure unobtainium and unrepairable without a wirebonder and an almost unobtainum tunnel diode. One could build a replacement using the same Maxim chip that Leo uses which has a rise time spec of 21 ps. It might well be a bit quicker with a smaller step. The input to the calibrator is a square wave so it should be possible to make a replacement for the crappy 250 ps rise time calibrator in the 11801C. Should be a very simple board and *very* popular with 11801C owners. I don't know when they changed from the marvelous <20 ps pulser to the 250 ps pulser, but learning that killed my interest in getting a C unless there is a way to put a better calibrator in it. 11801 #1 is equipped with an SD-22, SD-24, SD-26 and SD-32 set and now occupies a place of honor on my very small bench. On Saturday, March 27, 2021, 01:57:11 PM CDT, Sean Turner <[email protected]> wrote:
#yiv6493947978 #yiv6493947978 -- _filtered {} _filtered {} _filtered {}#yiv6493947978 #yiv6493947978 p.yiv6493947978MsoNormal, #yiv6493947978 li.yiv6493947978MsoNormal, #yiv6493947978 div.yiv6493947978MsoNormal {margin:0in;font-size:11.0pt;font-family:sans-serif;}#yiv6493947978 p.yiv6493947978msonormal, #yiv6493947978 li.yiv6493947978msonormal, #yiv6493947978 div.yiv6493947978msonormal {margin-right:0in;margin-left:0in;font-size:11.0pt;font-family:sans-serif;}#yiv6493947978 p.yiv6493947978msonormal3, #yiv6493947978 li.yiv6493947978msonormal3, #yiv6493947978 div.yiv6493947978msonormal3 {margin-right:0in;margin-left:0in;font-size:11.0pt;font-family:sans-serif;}#yiv6493947978 p.yiv6493947978msonormal41, #yiv6493947978 li.yiv6493947978msonormal41, #yiv6493947978 div.yiv6493947978msonormal41 {margin-right:0in;margin-left:0in;font-size:11.0pt;font-family:sans-serif;}#yiv6493947978 p.yiv6493947978msonormal311, #yiv6493947978 li.yiv6493947978msonormal311, #yiv6493947978 div.yiv6493947978msonormal311 {margin-right:0in;margin-left:0in;font-size:11.0pt;font-family:sans-serif;}#yiv6493947978 span.yiv6493947978EmailStyle34 {font-family:sans-serif;color:windowtext;}#yiv6493947978 .yiv6493947978MsoChpDefault {font-size:10.0pt;} _filtered {}#yiv6493947978 div.yiv6493947978WordSection1 {}#yiv6493947978 I don¡¯t know if they made changes to the self test suite, but this unit goes into an extended diagnostics mode that very definitely tells you what FRUs (field replacement units¡fancy euphemism for ¡°we don¡¯t do component level troubleshooting anymore¡±) may be responsible for each error code. I highly doubt those would be completely wrong, as that would waste the time of the service center people back when this unit was supported. There are *no* errors reported for executive functions or display functions. ? However, that¡¯s neither here nor there. I¡¯ve now reseated everything, but no dice on clearing any errors. ? Sean ? From: Reginald Beardsley <pulaskite@...> Date: Saturday, March 27, 2021 at 12:39 To: Jerry Hancock <jerry@...>, Sean Turner <[email protected]> Subject: Re: error codes ? You're assuming that the error reporting is correct. I'd advise not making that assumption. There is not enough data to analyze the messages except in a very general way and we know almost nothing about what signals are on what connections. KISS Pull each board and cable, then replace it. Go to the next board and repeat. Boot system. If errors show up repeat the process. That worked for my 11801 and Jerry's 11801C. It also worked for Jerry for the 11801 I got from him which is now throwing errors. I'll bet that when I do it tomorrow it will be happy again. My bench is not completely clean, but very close. BTW the 11801 loses the traces when powered off. On Saturday, March 27, 2021, 01:25:08 PM CDT, Sean Turner <[email protected]> wrote: ? ? Yes, I see that now. However, there are no faults in those areas. All the errors point towards the acquisition module and possibly the strobe driver. I did figure out the acquisition module removal. I re-seated everything in the acquisition module; unfortunately this didn¡¯t clear any of those faults. ? Funny enough, the prior owner never cleared their data, so there are a bunch of stored traces available. ? Sean ? From: Reginald Beardsley <pulaskite@...> Date: Saturday, March 27, 2021 at 12:09 To: Jerry Hancock <jerry@...>, Sean Turner <[email protected]> Subject: Re: error codes ? Yes, there are boards to pull. Look at p 6-14. The A17, A18, A14 & A15 all plug into the A13 motherboard. This is clearly documented on pp 6-50 to 6-56. The 11801 has 2 memory boards instead of just one. On Saturday, March 27, 2021, 12:47:48 PM CDT, Sean Turner <[email protected]> wrote: ? ? So there¡¯s really no cards to pull, per se. Everything is connected with ribbon cables. My hypothesis is the problem lies in the acquisition module based on the self test results. I am working out how to remove it, as the manual isn¡¯t perfectly clear on the matter. It () speaks of removing two Torx screws that hold a frame section in, but I can¡¯t find any diagrams that show where these screws are. ? Tomorrow is fine by me. ? Sean ? From: Reginald Beardsley <pulaskite@...> Date: Saturday, March 27, 2021 at 10:13 To: Jerry Hancock <jerry@...>, Sean Turner <[email protected]> Subject: Re: error codes ? You don't need any sampling heads installed. I'm doing a CS class from 2-3 pm EST so tomorrow would be the soonest I could do it. I think Jerry is busy today also. Did you pull all the cards from the backplane? IIRC they need to be in a specific order which is shown in the manual. It's quite a chore to reseat everything. IIRC I was not willing to dig as far as the head connector board because of the huge PITA it presented. I am quite amazed at how broken the autotools configuration for gnuplot-5.4.1 is trying to build on Ubuntu 14.04 LTS. God what a mess. It's depending on pkg-config which is broken. I think that imake has risen from the dead with a new name. On Saturday, March 27, 2021, 10:55:55 AM CDT, Sean Turner <[email protected]> wrote: ? ? Yeah, that sounds good. Let¡¯s do that once I get that sampling head you¡¯re sending me, so I can rule out the thing freaking out because there¡¯s no head present. ? I¡¯ve reseated all the connectors I can get to (seems to be mostly ribbon cables so far), but I haven¡¯t yet figured out how to get to into the plug in bay¡I will work that problem today. ? Sean ? From: Reginald Beardsley <pulaskite@...> Date: Saturday, March 27, 2021 at 08:32 To: Sean Turner <[email protected]>, Jerry Hancock <jerry@...> Subject: Re: error codes ? The T3314 is most likely bad connection. At least that is what Jerry Hancock found recently with his 11801C. I had similar experience. I had to completely reseat my 11801 twice to clear the errors. I should note the errors were not shown in the photo on ebay. Just the NVRAM error. These beasts do not like traveling. I think they are probably all bad connections. I'd suggest Deoxit, but getting at the backplane would be such an ordeal that just repeated reseating seems more reasonable. My first 11801 has been completely reliable once I had it working. I'd like to suggest that the 3 of us get on the phone together to discuss. I suspect that among us we can deduce the answers. I can drag my spare 11801 in once I clean off my bench and work on getting it going. It worked when Jerry foolishly sold it to me, but did not when it finally got here. On Friday, March 26, 2021, 10:00:07 PM CDT, Sean Turner <[email protected]> wrote: ? ? These are the codes I pulled out of the selftest: ? | Subsystem | Block | Area | Routine | Index | | Time Base | M/F I/F | Strobe Gate | Acq 1 | T3314 | | Main Acq | Acq 1 | Signal Path | Strobes | m1422 | | Main Acq | Acq 1 | Signal Path | Signal Path A | m1461 | | Main Acq | Acq 1 | Measurement | Filter A | m1521 | | Main Acq | Acq 1 | Measurement | A->B B->A | m1541 | |
Attilio
to navigate to use esc to dismiss