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The perfect function generator, does it exist ?

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Kiriakos-GR:
I did face an issue with an professional but old function generator.
At at higher frequencies the named voltage output ( Peak to Peak) above the 300KHz it starts to drop significantly,
more specifically the generator have as specs 20VPP 0-20MHz,  and at 300KHz the voltage drops to 5VPP.
And above 300KHz  it drops even more, to the point the output to become few mV.

Is this normal or expected ?

In theory I would  expect 20VPP in all the range of frequencies !!
Is out there the perfect Function generator, that has identical output in full range ?   

My small own small and cheap frequency generator 27KHz max, acts the same, but so far I was thinking that it was due the simplified design. 

Zad:
I think you would have to define "perfect".

20vpp equates to 8W into a Zo=50R, That is quite a lot of power, and a heck of a lot to ask from a signal generator.

Does it state what the characteristic impedance is, or what the test load impedance is?

Kiriakos-GR:
The impedance is adjustable to 50 or 600 ohm.

Even so I need 2.5VPP up to 2MHz, do I ask too much ?   

Conrad Hoffman:
There's either something wrong with it, or your measurement, or you've got it loaded too much. Even though a generator may have a 50 ohm output impedance, it's rare that they can drive 50 ohms to any large amplitude. It's important to understand the difference. It should be quite flat into a high impedance load over the full frequency range.

FWIW, the perfect function generator is the long gone Wavetek 185 sweep generator. It only goes to 5 MHz, but has separate dials for start and stop frequency. They had others with more bandwidth, but above a couple MHz I just switch to a real RF generator.

Richard W.:
Hello Kiriakos,

do you speak about sine wave or rectangular? du you measure the voltage with a scope or multimeter or even a hf-voltmeter?
Maybe your readings are caused by the frequency response of your measuring instrument. The output voltage of my HP 8111A is stable up to it's maximum frequency.


--- Quote from: Zad ---20vpp equates to 8W into a Zo=50R, That is quite a lot of power, and a heck of a lot to ask from a signal generator.
--- End quote ---

it's not this much power. You have to use RMS voltage for P=U²/R

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