Products > Test Equipment
Function generator with simultaneous modulations
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MarkL:
If you're unable to find a unit that does both burst and AM, you might want to take a look at doing the modulation externally and leave the burst count up to the function generator.

For a fast solution, you could grab an analog multiplier eval board and use that as your modulator.  You didn't say anything about your voltage, AM depth, or distortion requirements, but here's a range of possibilities from Analog Devices:

  http://www.analog.com/en/products/linear-products/analog-multipliers-dividers.html
maxwell3e10:
Yes, already have an external analog multiplier to do this, but was looking for something with more accuracy. I think old function generators would implement AM with an analog multiplier, while newer ones digitize the external modulation and do the multiplication digitally. I am not sure how DS345 does it.

If the basic functionality is there on some of these models, just not accessible through UI, that would be OK. Its just hard to tell without investing in the instrument.
joeqsmith:
I take it that it's not something that repeats where you could just upload the modulated wave and trigger it multiple times.  You want to modulate the burst live.   

What other requirements do you have? 

MarkL:
If you don't care about the precise number of cycles in the burst, you could do it with a function generator that has a gate input and an AM modulation input.  You would use a second function generator to feed the gate input on the first to create the needed burst size.  The second function generator could also be triggered to start the burst.

The old HP 8116A and the older Tek FG504 both have separate inputs for gate and modulation.  I tried it on both and they can both do gate and AM at the same time.  But if you were looking for a more modern unit, these definitely don't qualify.


EDIT:  I should also note that both units are also analog implementations, so they are not particularly accurate.  The FG504, however, has a phase-lock input so you could feed it a reference if you wanted an exact and stable output frequency.
maxwell3e10:
Yes, its possible to use arbitrary waveform, but its clunky because if the two frequencies are not easily commensurate, it needs to be very long. And to scan one of the frequencies requires updating the waveform every time.

The gate input could work, the only possible issue is that its typically not phase-synchronous, so can cause some little problems.

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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