Good New/Used Function Generator (which one) - Page 1
Forum section: electronics / beginners

author: AirScooter
author_rank: Contributor
timestamp: February 22, 2021, 02:15:09 pm
content: I have wanted/needed a Function Generator for some time. Recently, a memo from the department of "She Who Must Be Obeyed" reached my desk informing me that my request had been approved for a very moderatley priced Function Generator. My entire section went into a Victory Dance, I high pawed the dog. Now armed with fresh permission I am confused as to what the specs and/or the price and/or new or used.I have been reading a lot trying not to under equip myself and have come up with these mins from a site that offers to equip a hobbyist lab with the proper equipment. He has determined the following in regards a Function Generator:Don't but one unless:1. It does Sinewaves at 0.5Hz to 100MHz2. " " Square Waves 0.5Hz to 50MHz3. " " Triangle, ramp, and pulse at 700ns to 1000nsDo these look like reasonable specs to members.Thank youAirScooter

author: tunk
author_rank: Super Contributor
timestamp: February 22, 2021, 02:25:56 pm
content: It might help if you indicate how much your treasury department has set aside.And what are you going to use it for?

author: AirScooter
author_rank: Contributor
timestamp: February 22, 2021, 04:32:29 pm
content: There was no mention of a fixed sum in the inter-office communique I received. But, I am afraid I set a very bad precedent when I bought a like new LeCroy 9400 for $58 USD. She considers the Function Generator a secondary fixture in what she refers to as the room that smells like a burning plastics factory, my humble and very new, Electronics Lab.I guess my best chance would be something in the hundred dollar range. I know, I know, crazy right. Truth be told. I really prefer the old stuff. I am perfectly willing to leave the vacuum tube sets to Mr. Carlson, but something with a few whiskers that made a name for itself in the day would do me just fine. If I can get a handle on what that generator is, I will begin the search and attempt to have some kindly person "donate $$$" it to my burning plastics factory.I'm sure "She Who Must Be Obeyed" (The woman whos feet I am unworthy to wash) would agree.Thanks for the replyAirScooter

author: SilverSolder
author_rank: Super Contributor
timestamp: February 22, 2021, 04:46:05 pm
content: You can find nice older models, but they can be a bit, ahem, temperamental, and they tend to be big. I like the HP 3325A or HP 3325B units, for example, but you always have to prepare to repair when it comes to older equipment - no different than keeping an old muscle car on the road, in principle.A good way to get a whole batch of new instruments (including signal generator, scope, spectrum analyzer, etc.) in a tiny space for your lab is the Digilent Analog Discovery II, but you may have to save up a lot of kisses for the Ministry of Finance to get there!

author: rstofer
author_rank: Super Contributor
timestamp: February 22, 2021, 06:38:20 pm
content: Quote from: AirScooter on February 22, 2021, 02:15:09 pmAs long as you aren't looking for an Arbitrary Waveform Generator, the numbers may be fine. The Siglent SDG2082 AWG, which I have, is only good for sine waves to 80 MHz, square waves to 25 MHz and ramps to 1 MHz. It costs about $600. The 100 MHz version runs about $900 and it is only the sine wave that increases in frequency capability. Other waveforms are still limited to much lower frequencies.The neat thing about the Siglent AWG is that you can form a waveform by including harmonics of the chosen fundamental. That doesn't increase the maximum frequency but it does allow for some interesting waveforms. The harmonics can also be phase shifted.For your review, here is the User Manual for the SDG20xx series AWGs.https://www.jameco.com/Jameco/Products/ProdDS/2292927UsersManual.pdf

author: AirScooter
author_rank: Contributor
timestamp: February 22, 2021, 06:53:20 pm
content: Thank you for you very informative reply.I am afraid $600 is but a dream in the land of the WalMart Shopper where senior Fridays and triple coupons reign.I will look at this manual and try not to spoil my computer with envy.Thank you againAirScooter

author: MikeK
author_rank: Super Contributor
timestamp: February 22, 2021, 08:36:34 pm
content: What you going to be using the FG for matters, which you don't say. The quoted specs are presumptive. I have gotten lots of use from my 3MHz GWInstek SFG-1003. Some on here may need 100+MHz, others may not. You?

author: ledtester
author_rank: Super Contributor
timestamp: February 23, 2021, 07:28:54 am
content: I wouldn't spend too much money on a signal generator. The one I have is easily the least used piece of equipment on my bench.Here are some inexpensive ways to generate various wave forms:* audio frequency wave forms -- use your computer's sound output; good for sine waves, for other types of waves have a look at:https://stackoverflow.com/questions/4186735/how-to-output-a-square-wave-on-my-soundcardAnd here's an LCR meter program which uses your computer's sound output:https://www.eevblog.com/forum/testgear/artalimp-free-software-for-lcr-measurements-with-sound-card/And there are others like it on the web. Note also the Analog Discovery software mentioned in that thread.* fast clock signals --https://www.adafruit.com/product/2045* sine waves up to 30 MHz or so -- google "Arduino AD9833/AD9850"

author: wizard69
author_rank: Super Contributor
timestamp: February 23, 2021, 02:27:58 pm
content: Unless you have more details on why you have the specs you do, I'm not sure I could justify such a machine. Frankly you can get new and used function generators that run under 10MHz, pretty cheap these days. I'd look for one of these if it can cover a good portion of your needs and then later look for an RF signal generator or possibly a much more elaborate function generator. You can get instruments in this class new for under $300 and used for far less. If you go for a fixed function device, that is drop arbitrary waveform generation, and are willing to go E-Bay or China direct you can get equipment under $150 new. Maybe not as elaborate as you want but it highlights that there isn't much to these units these days. It should also put the prices on used equipment in perspective.In any event I have to agree with others here, unless you know exactly why you need the specs listed, function generators don't get a lot of use on the repair bench and maybe not on the development bench depending on what you are doing.

author: todorp
author_rank: Regular Contributor
timestamp: February 23, 2021, 03:07:35 pm
content: Maybe ADI ADALM2000 learning module might be suitable for you - it costs around 123 Euro from digikey. You get a swiss army knife tool :-).

author: rsjsouza
author_rank: Super Contributor
timestamp: February 23, 2021, 03:39:52 pm
content: I know it is not old iron, but the price/performance ratio of some of the Chinese products is quite high.Perhaps aUTG932E?I had good luck with a FY6600 30MHz function generator - no severe problems so far after about two years of use. However, I would be very careful as many others had terrible experiences with these function generators.

author: SilverSolder
author_rank: Super Contributor
timestamp: February 23, 2021, 03:43:09 pm
content: If @AirScooter is doing electronics as a hobby and a brain challenge, there is no doubt that having a way to generate waves, sending them into stuff (components and circuits), and looking at the results on the screen, should be considered a very basic thing to be able to do in your home lab setup. It doesn't have to be 100MHz, some people spend a lifetime looking at things below 20KHz (audio circuits). The higher the frequency, the more you have to know what you're doing - it totally makes sense to start in the audio range and work your way up.If you don't have a lot of money to spend, using a PC or laptop as a "test bench" for audio frequencies can be a great option.For much less than $100, you can get an external USB sound card (to protect your computer in case of "accidents") and maybe a USB isolator too (even more protection for your computer against "accidents"). The sound card can pump out wave forms, and also read them back in via its Line In jack, and display the results on the computer screen like an oscilloscope or spectrum analyzer (emulating thousands of dollars worth of equipment!).You can use the WaveForms software from Digilent on your computer to do this - the software is free and works with a sound card as well as working with the Analog Discovery II. Later on, you can upgrade the whole setup by getting an Analog Discovery II.Overall, this kind of approach is probably the best bang for the buck possible today, and it is capable of astonishingly good results with a half way decent sound card - and downright amazing results with an Analog Discovery II.

author: Electro Fan
author_rank: Super Contributor
timestamp: February 24, 2021, 02:57:44 pm
content: Quote from: rsjsouza on February 23, 2021, 03:39:52 pmI think the OP can reasonably use the UTG932E and probably the FY6900 as stalking horses (and either might turn out to be the winner, or maybe something else might be a better fit). If the OP studies the functions and performance specs of these models he can then use them as reference points from which to compare less expensive and more expensive alternatives either new or used.

author: bdunham7
author_rank: Super Contributor
timestamp: February 24, 2021, 05:04:53 pm
content: Quote from: AirScooter on February 22, 2021, 02:15:09 pmNo, that's silly. If you need 100MHz, great, get it. If you don't, you're likely either paying a lot more than you need to or, more likely, sacrificing a large, useful feature set that you might otherwise get at your budget. 50MHz square waves? Dream on. And I'm not sure what the last line means.The easiest way to get the most for your first signal generator is with an inexpensive DDS AWG like the Feeltech FY6900. If you want old-school 'quality', you may end up with a repair job instead of a working instrument. The HP 8116A models are pretty neat (although 50MHz max and no ARB), but typically need repairs and extensive calibration. You can buy a broken one for $75 on eBay and you just might be able to fix it....or not. Does your guru have any specific recommendations?

author: MikeK
author_rank: Super Contributor
timestamp: February 24, 2021, 06:43:48 pm
content: If you're not completely sure what you need, you're going to just have to buy something and use it. Only after using one will you understand your true needs. Get the Feeltech FY6900 and start using it. Reassess after a year.

author: Cliff Matthews
author_rank: Unknown
timestamp: March 14, 2021, 11:50:29 pm
content: Quote from: rsjsouza on February 23, 2021, 03:39:52 pmAccording to this, a slightly over-clocked $4 Raspberry Pi Pico AWG can hit 30Mhz as well.https://www.instructables.com/Arbitrary-Wave-Generator-With-the-Raspberry-Pi-Pic/What to do with the issue of a pesky 30Mhz output amp is quite another topic!

author: 3DEcho
author_rank: Newbie
timestamp: March 15, 2021, 11:17:37 am
content: Noob here, too. I bought a 60MHz Koolertron GH-CJDS66 FG on Amazon for about $150. From the reviews, it seemed to be a suitable mix of features + price. I've actually used it to generate low frequencies. They also make a 30MHz and 15MHz model for less $.

author: tautech
author_rank: Super Contributor
timestamp: March 16, 2021, 06:12:21 am
content: Quote from: bdunham7 on February 24, 2021, 05:04:53 pmNope, the 200 MHz SDG6022X does 80 MHz square and the next models up do 120 MHz and all with 2ns rise times.I get the feeling the OP has been set up to find such an instrument for bugger all $ which we know doesn't exist.

author: ricard2k
author_rank: Unknown
timestamp: March 17, 2021, 08:26:07 am
content: Thanks for the idea about the Arduino AD9833/AD9850! It looks great. I think that my next project will bis this.

author: SilverSolder
author_rank: Super Contributor
timestamp: March 17, 2021, 01:13:30 pm
content: Quote from: ricard2k on March 17, 2021, 08:26:07 amThat does look like a fun thing to play with!

author: rstofer
author_rank: Super Contributor
timestamp: March 17, 2021, 03:29:19 pm
content: In terms of a sine wave, it is likely that all frequencies within the bandwidth are needed. One application of this is generating Bode' Plots where there is a continuous range of frequencies.Square waves might be different. Perhaps 10 MHz, 25 MHz, 100 MHz (plus maybe a couple of others) might be the only frequencies ever needed. Buy a crystal oscillator for each as they are needed. You can get oscillators in 3.3V and 5VLike this for $1.32:https://www.digikey.com/en/products/detail/ecs-inc/ECS-2333-100-BN-TR/3927402That FY6900 might be a perfectly fine place to start. As mentioned above, use it for a year and see what you think.It is possible to spend a lot of money on an AWG and only use a small percentage of its capability. I bought the Siglent SDG2082X ($619 at Amazon) and it's a pretty nice AWG. But, seriously, it's a little over the top for my needs. I just happened to have a little money so I went wild. What in the world would I ever do with 80 MHz sine waves? I don't do Ham Radio... Audio ranges might be perfectly adequate for sine waves and crystal oscillators might be just fine for square waves. Or even ceramic resonators.Here's one for $0.44:https://www.digikey.com/en/products/detail/murata-electronics/CSTLS20M0X51-B0/9959613It turns out that I use my Analog Discovery 2 for most of my experiments. It has increased in price and is generally unavailable but it's a pretty slick unit it if ever comes back in stock. I like the old $279 price a lot more than I like the new $399 price. Talk about opportunistic pricing!

author: SilverSolder
author_rank: Super Contributor
timestamp: March 17, 2021, 07:08:34 pm
content: Quote from: rstofer on March 17, 2021, 03:29:19 pmThe AD2 is an ingenious tool for beginners, intermediates, and even pros to have around.Talk about not being prepared for the success, though... Digilent has totally failed to take advantage of the market opportunity (seemingly unable to arrange for it to be manufactured fast enough... they have been out of stock since forever). And nobody has stepped in with a competing product...

author: rstofer
author_rank: Super Contributor
timestamp: March 18, 2021, 05:13:09 am
content: Quote from: SilverSolder on March 17, 2021, 07:08:34 pmAnalog Devices has the ADALM2000 which is the same idea. I haven't compared specs but I played with the software once. It is nowhere close to Digilent's Waveforms...https://wiki.analog.com/university/tools/m2kI think Digilent got caught up in the Covid thing. There are no in-person lab courses at the universities so all of the students had to rush out and buy <something>. Many of them no doubt bought the AD2.That and supply chain problems according to DigilentAnd the fact that they have been bought by National Instruments and NI has all kinds of higher cost competing devices.http://dangerousprototypes.com/blog/2013/01/24/national-instruments-acquires-digilent-inc/The higher price on the AD2 isn't justified, it seems opportunistic to me. I have been a Digilent customer for a very long time (as a hobbyist) and I am getting very disappointed in them.

author: SilverSolder
author_rank: Super Contributor
timestamp: March 19, 2021, 12:43:26 am
content: National Instruments is not known for their aggressive pricing...

author: Lowkus
author_rank: Regular Contributor
timestamp: March 19, 2021, 01:33:08 am
content: If I'm trying to replicate a function gen square wave using a sound card, should I shape the square wave using additive sinusoidal calculations to approximate a square wave? Or should it be made using a binary ON/OFF structure to give it a nearly instant slope?

author: SilverSolder
author_rank: Super Contributor
timestamp: March 19, 2021, 01:55:35 am
content: Quote from: Lowkus on March 19, 2021, 01:33:08 amI'd try a crude 101 square wave first and see what it looks like?You can calculate the expected rise time depending on the sample rate you use, look on the scope and check that it looks right?

author: Cliff Matthews
author_rank: Unknown
timestamp: March 19, 2021, 01:55:59 am
content: Nice fast edges? 74AC14 comes to mind...** .. and you can power it from a ~22 ohm current limiting resistor off a nearby USB port

author: tautech
author_rank: Super Contributor
timestamp: March 19, 2021, 02:08:14 am
content: Quote from: Cliff Matthews on March 19, 2021, 01:55:59 amWhy limit the current ? Won't that possibly slow the edge ?

author: Cliff Matthews
author_rank: Unknown
timestamp: March 19, 2021, 02:20:44 am
content: Quote from: tautech on March 19, 2021, 02:08:14 amRight. I trusted the OP might know a small el-cap after the safe USB current limit would be prudent.

author: tautech
author_rank: Super Contributor
timestamp: March 19, 2021, 03:22:27 am
content: Quote from: Cliff Matthews on March 19, 2021, 02:20:44 amOK, gotcha.I have a 74AC14 pulser on the build to be powered from USB so I did wonder if I'd missed something but apparently not.However while a PCB is all routed and ready to go I won't have time to get back to it for a month or 2.

author: ledtester
author_rank: Super Contributor
timestamp: March 19, 2021, 04:02:12 am
content: Quote from: Lowkus on March 19, 2021, 01:33:08 amI'd first try the binary ON/OFF approach and see you get. Or see what this web page produces (you can select between sine, square, triangle and sawtooth waves):https://www.szynalski.com/tone-generator/This page suggests a more sophisticated approach - basically you try to undo the effects of the hi-pass filter in the sound card:https://stackoverflow.com/questions/4186735/how-to-output-a-square-wave-on-my-soundcardIn any case I don't think you're going to get good results for more than a couple of kHz.btw... this looks like an interesting way to add a DC offset to a sound card generated wave:https://www.instructables.com/PC-Sound-Card-Signal-Generator-Interface/

author: SilverSolder
author_rank: Super Contributor
timestamp: March 19, 2021, 01:52:19 pm
content: It could be cool to drive a 74AC14 from the sound card output... that would be flexible, and probably generate some very nice squares.

author: Cliff Matthews
author_rank: Unknown
timestamp: March 19, 2021, 06:43:17 pm
content: Quote from: SilverSolder on March 19, 2021, 01:52:19 pmEvan cooler to provide a fundamental on one channel and shape it with the other. Maybe someone's next "Altoids" project?

author: Lowkus
author_rank: Regular Contributor
timestamp: March 20, 2021, 04:27:01 am
content: I'm using a Fireface UFX video card (rack mount). With some effort building an ensemble in Native Instruments Reaktor hopefully I can get some usable wave output.

author: gf
author_rank: Super Contributor
timestamp: March 20, 2021, 08:15:02 am
content: Quote from: Lowkus on March 19, 2021, 01:33:08 amAny truncation of the fourier series (i.e. both cases you mentioned) is eventually supposed to suffer fromGibbs phenomenon.If you don't like the resulting overshoot and ringing, you need to renounce rise time and make the edges significantly softer.EDIT:Besides that, any DDS-generated square wave with "hard edges" is supposed to suffer from jitter, unless both, f*D=fs/N and f(1-D)=fs/N are granted (where f is the square wave frequency, fs is the sampling rate, D is the square wave duty cycle (0...1) and N is an integer >= 1), which imposes a severe limitatoin on the frequencies which can be generated jitter-free (with jitter-"free" I mean as good as the sound card can do eventually).Consequence: At least for higher frequencies and if steep edges are desired, it is not the best idea to generate a square wave in the discrete domain, and then convert the sampled signal to analog by applying a reconstruction filter (what the soundcard eventually does). In this case a better approach is to generate a sine wave with the desired frequency in the fist place and convert the analog sound card output to a square wave with a comparator. I guess that's what SilverSolder has in mind when he says "It could be cool to drive a 74AC14 from the sound card output".