Modern Equivlent to Tek 284 - Page 1
Forum section: electronics / general

author: Zenwizard
author_rank: Regular Contributor
timestamp: January 22, 2019, 05:14:25 pm
content: Does anyone know of a modern equivalent to a Tektronix 284 Pulse generator? I am doing the final touches on a 485 scope cal and they seem to be unabtainaiom on the usual places. I don't mind buying new as long as the pricing is not crazy as cal gear can some times get.Thanks

author: Tom45
author_rank: Frequent Contributor
timestamp: January 22, 2019, 07:25:52 pm
content: Even if you could find a 284 you probably wouldn't want it after you see the prices for something that adapts to those GR connectors.

author: LazyJack
author_rank: Frequent Contributor
timestamp: January 22, 2019, 07:39:11 pm
content: I guess something like the Tektronix PG506 and other associated TM500 calibration modules are what you need.

author: grbk
author_rank: Contributor
timestamp: January 22, 2019, 07:46:28 pm
content: Quote from: LazyJack on January 22, 2019, 07:39:11 pmPG506s aren't super cheap either, but they do come across ebay fairly frequently. Seems like demand for these is relatively high and buy-it-now ones at a reasonable price get snapped up quickly. In my limited searching I haven't come across any better alternatives, but I would be interested in other options if anyone has suggestions.

author: dzseki
author_rank: Frequent Contributor
timestamp: January 22, 2019, 08:15:05 pm
content: If only for fast pulse generation, then what about Leo Bodnar's pulse generator?

author: macboy
author_rank: Super Contributor
timestamp: January 23, 2019, 03:37:43 pm
content: Quote from: dzseki on January 22, 2019, 08:15:05 pm+1The main use of the fast rise pulse from the 284 is to perform the mid and high frequency compensation of the scope's vertical amplifiers (and maybe the probes as well). For that purpose, Leo Bodnar's pulse generator will work very well. It doesn't matter that it is a 10 MHz 50% square wave instead of20050 kHz. The rise time and pulse shape/flatness is most important. The output voltage is rather limited, only 1 Vpp back termiated into 50 ohms, or 2 Vpp not terminated, but that's higher than the 284 could do. You may need inline 50 ohm attenuators for use with the lower voltage vertical settings.edit: I have a HP 8131A pulse gen that would work as well. The rise time is fast at <200 ps, but not quite as good as the Leo Bodnar unit, and it is a few orders of magnitude bigger. It has the benefit of adjustable repetition rate and width, as well as adjustable output voltage and offset, so it could be set up to emulate the 50 kHz, 1 us, 200 mV pulse of the Tek 284. It is digitally controlled and plenty accurate enough to use to calibrate the timebase/sweep on any analog scope. If you (or anyone) is interested in such a beast, let me know... it is one of quite a few items slated to fall victim to a general lab cleanup/downsize (mandated by the facilities manager, aka wife).

author: Howardlong
author_rank: Super Contributor
timestamp: January 23, 2019, 03:48:43 pm
content: I agree, Leo's pulse generator may well work very well for this purpose.

author: David Hess
author_rank: Super Contributor
timestamp: January 23, 2019, 09:14:30 pm
content: Quote from: LazyJack on January 22, 2019, 07:39:11 pmThe PG506 by itself is not fast enough. It would need to be combined with a 067-0681-01 or similar tunnel diode pulser which the PG506 was designed to drive.Leo Bodnar's fast pulse generatoris probably the best commonly available solution for this type of calibration. BNC (or SMA) RF attenuators can be used to lower the signal level if necessary and I have collected a whole set for exactly this application.

author: Zenwizard
author_rank: Regular Contributor
timestamp: January 24, 2019, 02:30:40 am
content: I have 2 of Leo's pulser's I had not though of turning up the voltage and then putting an attenuator on it to help flatten it out. The PG506 which I have is good up to 200Mhs at it only have a 1nS rise time. Are the Leo pulsers ok for flatness? They seemed to kind of ramp up to final voltage, or am I being just a bit to picky? I do know I am asking for sub nano second clean edge square waves which is not at all easy to attain.

author: Zenwizard
author_rank: Regular Contributor
timestamp: January 24, 2019, 02:36:55 am
content: How much is the HP going for?

author: dzseki
author_rank: Frequent Contributor
timestamp: January 24, 2019, 06:24:30 am
content: Quote from: Zenwizard on January 24, 2019, 02:30:40 ama.) The 485 has a self rise time of ~1ns, Leo Bodnar's pulse generator has ~20ps, so even if the transition is not perfectly smooth, I don't think it will matter much.b.) If you have access to a much faster scope you can characterize your pulse generator, and "correcting its deficiencies" with eyballing when adjusting the 485.c.) I'd rather not use a pulse generator for frequency flatness rather than verifying the ultimate bandwidth, as overshoot is always inherent to them, for flatness I'd use a levelled (RF) signal generator instead.

author: Zenwizard
author_rank: Regular Contributor
timestamp: January 25, 2019, 11:45:02 pm
content: But the leveled RF generator will only give you a sine wave correct?

author: dzseki
author_rank: Frequent Contributor
timestamp: January 26, 2019, 09:06:32 am
content: Yes, set the horizontal sweep to not see the sine per se, only the "envelope" then sweep through, and see how smooth the frequency response is. Obviously it won't be super flat, but you may be able to adjust just as well, it is maybe a little more time consuming. Also a little peaking ner the corner freq. Helps with the pulse response.