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Function generator with simultaneous modulations

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tautech:

--- Quote from: maxwell3e10 on January 19, 2017, 04:03:25 am ---I wonder if I contact the manufacturers, if I would get a response one can actually trust, as its a relatively obscure feature.

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Siglent have application engineers in Ohio, give them a yell.
http://www.siglentamerica.com/contact_us

Siglent America:

--- Quote from: maxwell3e10 on January 17, 2017, 06:05:14 am ---I am looking for a function generator that can simultaneously be controlled by burst count and external amplitude modulation. It seems most of them allow only one at a time but this is poorly documented.  DS345 from Stanford research systems can do it, but its pretty old and only allows 30000 burst counts, while I need 10^6, as most modern ones do. Any suggestions? Perhaps someone has used this mode or would be willing to test theirs.

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Hello,
We were informed of your application so we scratched our collective heads to see if there was a way to do this using two units, the channel summing mode, etc. The basic problem is that we cannot do burst and modulation at the same time. So we have two possibilities on this, if you are willing to do some extra work:

1) Connect to a PC and program the instrument to output the desired AM signal. Before enabling the output, calculate the time required for the desired number of bursts. Enable the output for the time calculated previously. After the time expires, set the amplitude to 0V (or as close as you can). Shutting off the output will stress the relay and could lead to premature failure if it’s pushed too hard by excessive switch counts.

2) Use CH 1 to generate the desired AM signal. Run that to an external switch or gate You could use a simple FET gate using only a few components. Now use CH 2 from the generator to drive the gate input of your FET switch/gate circuit.

Interesting application. Please let us know what you decide to do.
Good luck!

MarkL:

--- Quote from: maxwell3e10 on January 19, 2017, 04:03:25 am ---The gate input could work, the only possible issue is that its typically not phase-synchronous, so can cause some little problems.

--- End quote ---
What do you mean by "phase-synchronous"?

If you're referring to the start and stop of the waveform, the gate controls the number of full cycles output of the selected waveform.  The gate is not a simple on/off of the output.  For example, if your output waveform is a sine, the sine will start and stop at 0 degrees.  Some function generators allow you to select the starting phase from -180 to 180 degrees, but it will still always be an integer number of cycles as controlled by the gate input.

If by "phase-synchronous" you mean that you want the carrier to be in phase with itself from burst to burst, then perhaps what you want *is* a simple on/off of the output.  In which case a CMOS SPST switch on the function generator output, controlled by the burst signal, might work for you.

Or are you looking to somehow synchronize the burst or carrier start phase to the AM input?

maxwell3e10:
Thank you for attention to the forum. There are a number of ways to do it using external components, either to generate AM modulation with a multiplier or to generate burst with a switch. My hope would be to find an internal solution. This should be possible in principle, but depends on the method in which the burst mode is implemented, as an (internal) arbitrary wave or as a continuous wave with a separate counter.

Based on my reading of various manuals, my best guess is that BK Precision 4078B might be able to do it, as the modulation and running mode are separate functions. Also it has 10 ! inputs on the back, so all features are available for both channels at all times.

maxwell3e10:
Regarding gate modulation, I am not sure if its usually an integer number of cycles or simple on-off. I think some function generators have an option for either, but I haven't checked which is more common in general.
What I would prefer is the starting phase of the carrier to be the same at the gate trigger.

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