Sweep generator for function generator - Page 1
Forum section: electronics / beginners

author: M0BSW
author_rank: Frequent Contributor
timestamp: August 12, 2013, 03:41:23 pm
content: HiMy function generator, does not have sweep built in but does have Sweep input does anyone know of a circuit I can build as an add on so I can give my function generator that function please. simple one if possible.

author: w2aew
author_rank: Super Contributor
timestamp: August 12, 2013, 04:04:32 pm
content: It's likely that the Sweep input is a voltage-controlled-frequency input. Therefore, if you apply a sawtooth waveform, you should get a sweep. You can verify this from your documentation, or even experiment with a variable DC supply - apply a DC voltage to this input and not the frequency, then change the DC voltage and note the new frequency.If you find that this input works this way, then a simple sawtooth generator would be all you need to make a basic sweep generator. I've got a video on my channel that shows a sawtooth generator that would be a good starting point. I also have on one the basics of sweep generators that you might find helpful too.

author: M0BSW
author_rank: Frequent Contributor
timestamp: August 12, 2013, 04:24:19 pm
content: Quote from: w2aew on August 12, 2013, 04:04:32 pmThank You Alan I''ll take a look, DC voltage I'm going to do now

author: M0BSW
author_rank: Frequent Contributor
timestamp: August 12, 2013, 04:35:13 pm
content: Quote from: w2aew on August 12, 2013, 04:04:32 pmHi Alan, This is what I've done set the funct/gen to10K then zero'd it on the frequency counter .0000, then I applied 5 volts to the sweep input and got a reading of .1370, so would your sawtooth gen give me a sweep, as I have a need for sweep generation.Paul de M0BSW

author: w2aew
author_rank: Super Contributor
timestamp: August 12, 2013, 06:08:34 pm
content: Quote from: M0BSW on August 12, 2013, 04:35:13 pmHmmm - doesn't sound like it moved the frequency much - I'm assuming that it changed from 10,000Hz to 10,137Hz. If I am misinterpreting your comments, let me know. Does the manual or datasheet for the function generator say anything about the specs for this sweep input?

author: M0BSW
author_rank: Frequent Contributor
timestamp: August 12, 2013, 06:57:24 pm
content: Quote from: w2aew on August 12, 2013, 06:08:34 pmHi AlanOk started it again f/g is set at 100.00 khz on the freq counter power supply is at 1.7 volts reading now on frquency counter is 568.00 khz. manual states at 1.7 volts range sweep is 500khz, hope that means something to you, if I go to 0.4 volts its should sweep to 120 so trying that results are at 0.4 volts its121.02..

author: w2aew
author_rank: Super Contributor
timestamp: August 12, 2013, 07:05:45 pm
content: Quote from: M0BSW on August 12, 2013, 06:57:24 pmYou should take a couple of measurements around the frequency range that you are interested in - so that you can plot the output frequency vs. the sweep voltage. Once you know that characteristic, then you know what voltage ramp (sawtooth) you'll need to apply to create the sweep you need. You can then take the output of the sawtooth generator, condition it with an op amp circuit to adjust it's magnitude and offset to give you the sweep range you need.

author: M0BSW
author_rank: Frequent Contributor
timestamp: August 12, 2013, 07:19:28 pm
content: Quote from: w2aew on August 12, 2013, 07:05:45 pmThank you Alan , I have a better understanding now, I'll put it into practice tomorrow, thank you for taking the time to explain it, also I watched your video ready for my weekend build.

author: w2aew
author_rank: Super Contributor
timestamp: September 09, 2013, 07:21:50 pm
content: Quote from: M0BSW on August 12, 2013, 04:24:19 pmI put together a video that shows a fairly flexible ramp generator that can be used with the "voltage controlled frequency" input of many function generators in order to make it a sweep generator.

author: M0BSW
author_rank: Frequent Contributor
timestamp: September 09, 2013, 08:17:51 pm
content: Thank you for putting this together Alan, it would have taken me a long time, to get anywhere near, I've got some time off this week so I'll do the build, I've already soldered a 555 & a Lm324n , on the board. I do seem to have a fascination with these generators and how they work, a long with test gear in general. I also found it very interesting the tracking generator, you were using checking the filters on the linear, they look a serious build. and I think expensive I would imagine as is the spectrum analyzer that goes with them, even on E-Bay they command a high price., I compliment you on your excellent and informative videos always a pleasure to watch.Paul de M0BSW