Inexpensive signal generator? - Page 1
Forum section: electronics / testgear

author: ultrarunner2018
author_rank: Contributor
timestamp: October 13, 2018, 01:24:05 pm
content: Hi;Now that I have the Siglent SDS1104X-E oscilloscope, I'm ready to start building projects and experimenting.Well, almost...I don't own a signal generator.I do own a Raspberry Pi 3 b+, and know that I can use it to generate square waves up to about 250Mhz, but what I really want is sine, triangular, and square wave capability.I have been doing some reading on Arbitrary Waveform Generators (AWG), but not sure I really need anything more than a dual-channel (I want to experiment with signal mixing and harmonics) signal generator.I originally thought I could use my RigExpert AA-170 antenna analyzer as a signal generator from 100Khz up to 170Mhz, but when I put it on the scope, I realized that it will only generate square waves up to 30Mhz, then it switches to an odd-order sub-harmonic to generate higher frequencies. This was a bit of a mystery as I adjusted the frequency to 30Mhz, then went one step above, and saw the output jump down to 10Mhz. Then I re-read the manual and understood that it was doing what it is supposed to do.For signals in the audio range, I can use my Pi with the Audio Injector sound card, or my Windows 7 PC with any audio software (I use Reaper) to generate a tone. But I have found that on the PC, the signal is not so stable. It moves about on the scope, and is difficult to trigger properly. Perhaps it would be more stable from the Pi, but I haven't tried that yet.In any case, I need something capable of generating signals from audio to RF.I have seen these, ubiquitous ones on Ebay for around $100 for the 60Mhz model, and $50 for the 24Mhz model:https://www.ebay.com/itm/RD-JDS6600-Series-60MHZ-Digital-Control-Dual-channel-DDS-Signal-Generator-In-USA/232941588491?epid=27005755217&hash=item363c66900b:g:deoAAOSwJb5Zt4WT:rk:42:pf:0These are available in many brands, but are obviously the same inside the case.I guess one of these would suffice in getting me started, and I certainly don't have a lot of money to spend on this, since I already spent $500 on the scope.Your suggestions?ThanksUltrarunnerEdit: After I posted this, I began reading some of the user reviews for the Ebay item I linked to. Unfortunately, these units fail miserably at the HF (10-30Mhz) range, and that is where I want to be doing much of my work. So I guess I need to look beyond these apparently falsely advertised products.Perhaps a vintage HP, Tek, Fluke, Agilent, etc that will take up 1/2 my workbench space, or need to sit on the floor would be a better way to go?

author: tautech
author_rank: Super Contributor
timestamp: October 13, 2018, 07:22:57 pm
content: Don't overlook having to save a bit so to get an AWG that can be 'driven' by the X-E for its Bode plot functionality.There are a few lower cost options from Siglent, the cheapest being their SAG1021 but being 5V USB powered its P-P output levels are a bit miserable.Of their standalone units a SDG830 would be a better choice for $332 but it's still only a single channel unit.The SDG1032X would be the cheapest 'good' choice and if you want to 'improve' it to the 60 MHz model you'd have 60 MHz sine and square plus the Bode plot functionality in the 4ch X-E.The best low lost model would be a SDG2042X but sadly square waves stop at 25 MHz for all the SDG2000X series models, hacked or not.

author: nctnico
author_rank: Super Contributor
timestamp: October 13, 2018, 07:28:41 pm
content: IMHO you can't go wrong with the JDS6600 signal generators. They are cheap for what they do and it will take a long time before you grow out of it.

author: DaJMasta
author_rank: Super Contributor
timestamp: October 13, 2018, 08:24:00 pm
content: It's worth searching the forums for the JDS and Feeltech review threads, they're widely discussed around here and really seem to represent some of the best options around $100 or so.If you want to spend for more, there's the external module and firmware upgrade for your scope that Siglent offers, then there's the entry level Siglent and Rigol function gens which, to varying degrees, can give you what you're looking for. I think triangle wave is going to be a major sticking point, though, because generating a triangle at 30MHz is not something I see a lot in entry level signal generators. If that's not a requirement, it shouldn't be hard to find triangle waves to 10 or 15MHz in many models.While older sig gens can be good... they usually aren't much cheaper than entry level Siglent/Rigol versions, and as you know they're often much larger. You can sometimes pick up the smaller Agilent ones for around $200, but they're going to go up to like 15MHz, not 30 or 60, for sure.

author: ultrarunner2018
author_rank: Contributor
timestamp: October 14, 2018, 03:32:13 am
content: Thanks guys;I would love to get the 'add-on' for my scope, so maybe I should just hold off a while longer until I can afford that option.I really don't understand Bode plots yet, so I need to do some more reading.I'm not sure why I even mentioned triangular wave. I have no specific need for it, but thought it would be 'nice to have', but certainly wouldn't need it for frequencies above 1Mhz or so.In the meantime, I am going to rig up my Pi to generate square waves and play around with that for a while.

author: tautech
author_rank: Super Contributor
timestamp: October 14, 2018, 04:17:46 am
content: Quote from: ultrarunner2018 on October 14, 2018, 03:32:13 amSome simple examples of a Bode plot on a 1-30 KHz band pass filter here:https://www.eevblog.com/forum/testgear/siglent-sds1204x-e-released-for-domestic-markets-in-china/msg1435854/#msg1435854And a follow up in reply #550.Bode plots are also known as Sweep Frequency Response Analysis (SFRA) and good example from rf-loop is on P1 of the thread.

author: Sceeker
author_rank: Newbie
timestamp: October 14, 2018, 10:11:00 am
content: Quote from: nctnico on October 13, 2018, 07:28:41 pmI second this, they are really great andcheapsignal generators to get started with.The SAG1021 for your scope is really great, but not cheap at all (around 300$).The choice's yours but I think I would personally go for the JDS6600 for the moment.

author: tkamiya
author_rank: Super Contributor
timestamp: October 14, 2018, 03:13:13 pm
content: To me, requirement for RF generators are so different from Audio frequency generators that they cannot be accommodated in one. For example, for RF, levels are necessary down to microvolts where as on audio, few volts are not unheard of. Also, shielding of RF is critical where as AF, it is not. Wave shape is important on AF, not so with RF.All of mine are used HP that I picked up from eBay.

author: ultrarunner2018
author_rank: Contributor
timestamp: October 16, 2018, 12:44:45 pm
content: OK. Clicked tautech's link to the Bode plot. Turns out I've been seeing those plots for a long time, mostly when reading tech sheets on amateur radio gear, but I never knew what they were called.Now I have a few questions:What is the 30x trial of the AWG function in the SDS1104X-E? What good does a trial for a function that requires additional hardware that I need to purchase anyway?Do I need to purchase a license for Siglent's AWG software (in the scope) in order to use Bode plots (from any AWG)?There doesn't seem to be much explanation of how the AWG option works in Siglent's docs.From what I've read about Siglent's AWG option for the SDS1104X-E, it's only good to 25MHz for sine, and much lower than that for square waves. Sounds like I'd be better off with one of the less expensive models that works to 60MHz; of course those inexpensive models aren't AWG, just signal gens, right? But then, I really don't think I need an AWG for now.Edit: Watched a YouTube vid of the JDS6600 teardown ().I am worried about that 20min shut-down. Have they fixed it yet? That would certainly be a 'deal breaker', especially if you need to set it up all over after each reboot.Also noticed no shielding of the enclosure. That could be an issue when working at HF frequencies, and I am trying to listen to (or participate in) a QSO.

author: tautech
author_rank: Super Contributor
timestamp: October 16, 2018, 06:15:01 pm
content: Quote from: ultrarunner2018 on October 16, 2018, 12:44:45 pmThe SAG1021and anySiglent AWG can supply the swept sine wave for Bode plot usewithoutthe AWG license. Bode plot is a 'plug and play' feature for the four channel X-E's. The 2nd and 3rd stage filter plots are unique to the X-E Bode plot.The license is only necessary (after Trial times have expired) to allow the SAG1021 to be used as an independent AWG controlled from the UI within the SDS1*04X-E.QuoteThis indicates the SAG1021's capability:https://www.siglentamerica.com/accessory/sag1021/External Arbitrary Waveform GeneratorAccessory for use with the four channel SDS1000X-E oscilloscopes only. Output Sine, Square, Ramp, Pulse, Noise, DC and 45 built-in waveforms.The arbitrary waveforms can be accessed and edited by the EasyWave PC software.Further info on its spec are in the SDS1*04X-E datasheet.QuoteBetter capability and particularly output drive is available in any of the SDG standalone models.

author: nctnico
author_rank: Super Contributor
timestamp: December 25, 2019, 11:51:24 am
content: Amplitude. Most of the options you listed can't drive 5V logic.Also: would you want to drive a relay from your oscilloscope's function generator (if it can provide enough signal to do so)? For that I have a cheap Feeltech generator. Think about power cycle testing.

author: Old Printer
author_rank: Frequent Contributor
timestamp: December 25, 2019, 04:40:09 pm
content: Make sure you read the specs closely. Most units in the lower price ranges that are labeled at 60 MHz will only put out a clean square wave at 25 MHz and the triangle/arbitrary are usually maxed at 10 MHz. The FeelTechs are considered best bang for the buck, but do your homework so as not to be disappointed.

author: JUNCE LEE
author_rank: Newbie
timestamp: January 11, 2020, 02:36:47 am
content: The square wave signal of my JDS6600 performed well at 15MHz, the overshoot is small and it does not jitter!

author: boB
author_rank: Frequent Contributor
timestamp: November 06, 2020, 11:48:56 pm
content: Old thread I know...I just bought one of these and I really like it ! Especially for the price of around $100 USDboB

author: radiolistener
author_rank: Super Contributor
timestamp: November 07, 2020, 12:32:54 am
content: There is also new PSG9080. PSG9080 is similar to JDS6600, but PSG9080 has much better front panel and extended frequency range.