Function Generator Question - Page 1
Forum section: electronics / beginners

author: tkgmomosheep
author_rank: Newbie
timestamp: November 25, 2018, 09:12:51 am
content: I recently acquired a second hand function generator DG3121A, I tried the built-in self-test and it passed.But I am having trouble using the modulation function.I am using a DS1054Z(hacked) to see the generator output with and without 50ohm termination(using the high impedance mode and manually set the output to 50ohm), but doesn't seem to be able to see any modulation at all.Below are the images of the test setup.Please let me know if it's my fault or the generator is not working properly.Thank you!https://imgur.com/a/H6pPBOb

author: Brumby
author_rank: Unknown
timestamp: November 25, 2018, 09:34:40 am
content: At 1 microsecond per division, you are not going to see the modulation (you are only looking at 0.18% of the modulation waveform). Don't be fooled by the image presented on the function gen. It's only representative. To see the 150 Hz modulation, the 2.5 MHz carrier will become a fuzzy haze.Slow down your timebase. Try 1ms per division or even slower.

author: tkgmomosheep
author_rank: Newbie
timestamp: November 25, 2018, 10:14:03 am
content: Thanks for the reply!I tried it with a 1ms and the images are attached in the link.https://imgur.com/a/SwFHf2BI am also wondering why the Vpp will drop significantly no matter what AM depth I set it to.Actually I wanted to try out the intensity gradient display of the oscilloscope with an AM signal.Would you mind telling me how to set the scope and the generator up the connection required?

author: HB9EVI
author_rank: Frequent Contributor
timestamp: November 25, 2018, 10:31:58 am
content: Obviously you set the carrier on 2,5kHz not 2,5MHzto see the intensity gradient, you have to go much higher than 2,5kHz for the carrier

author: tkgmomosheep
author_rank: Newbie
timestamp: November 25, 2018, 12:49:21 pm
content: I tried with a much higher carrier fruquency at 1Mhz and modulate it with 1khz 100%.But still not the result I was expecting.I tried both Normal and HighRes mode and both yielded similar result.https://imgur.com/a/ASeXw2o

author: HB9EVI
author_rank: Frequent Contributor
timestamp: November 25, 2018, 01:27:52 pm
content: show for once just the settings of the FG and not the scope screen

author: tkgmomosheep
author_rank: Newbie
timestamp: November 25, 2018, 01:38:21 pm
content: Here it is.https://imgur.com/a/6ONtEKN

author: HB9EVI
author_rank: Frequent Contributor
timestamp: November 25, 2018, 03:32:15 pm
content: looks okis the 'Mod' button lit up?

author: tkgmomosheep
author_rank: Newbie
timestamp: November 25, 2018, 03:32:54 pm
content: Yes, it is.

author: HB9EVI
author_rank: Frequent Contributor
timestamp: November 25, 2018, 03:40:30 pm
content: did you already try with an external source?

author: tkgmomosheep
author_rank: Newbie
timestamp: November 25, 2018, 04:23:43 pm
content: I have not. But I only have one function generator, how can I generate a 1khz signal?

author: rstofer
author_rank: Super Contributor
timestamp: November 25, 2018, 08:13:13 pm
content: Have you tried the procedure on page 3-12 here:https://assets.tequipment.net/assets/1/26/Documents/Rigol/dg3000_guide.pdfI would try this first as it should produce a signal that matches the description.

author: tkgmomosheep
author_rank: Newbie
timestamp: November 26, 2018, 04:26:18 am
content: I did try to follow the instructions on the manual for both sine and am modulated sine setup, the sine outpur perfectly fine, but the modulated output looks tge same as pure sine even at different time base.

author: Brumby
author_rank: Unknown
timestamp: November 26, 2018, 11:41:41 am
content: Sorry for my misdirected suggestions. I misread the function generator carrier frequency.In my defence, I'm not used to commas in decimal places - and with the inverted use of commas and decimal points in some parts of the world... well...

author: tkgmomosheep
author_rank: Newbie
timestamp: November 29, 2018, 09:11:17 am
content: I tried with 1Mhz carrier frequency and 10khz modulation and it makes no difference.Is it normal for the amplitude to drop from 5Vpp to 1.1Vpp when Modulation is enabled? I am using x1 in the scope and the function generator said it's outputting 5Vpp.