Author Topic: WaveTek function generator - unexpected amplitude in MHz range  (Read 435 times)

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Offline beowulfenator

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Hi!

I got my hands on an old WaveTek model 20 2MHz function generator. The schematics are available:

http://bama.edebris.com/manuals/wavetek/20/

My unit works, but at higher frequencies there is some attenuation for all three waveforms (sin, triangle, and square). At 200 KHz and below the amplitude is the same, but as the frequency increases, the amplitude goes down. At 2MHz the amplitude is about half of what I have at 200 KHz. This attenuation happens at all amplitude settings, so 20V p-p goes down to 10V p-p and 4V p-p goes down to 2V p-p.

I'm using a 10MHz scope with a 10MOhm/40pF input. The manual suggests to terminate the cable with a 600 Ohm resistor, and I'm not doing that (can't do that easily, the scope uses an unusual connector and its pins are not exposed).

Is this the expected behavior of this generator?
 

Offline David Hess

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Re: WaveTek function generator - unexpected amplitude in MHz range
« Reply #1 on: June 16, 2018, 09:12:11 pm »
That much amplitude variation is consistent with the specifications so I suspect it is working fine.  Unlike most function generators, it has a 600 ohm output impedance intended specifically for audio applications instead of 50 ohms for general purpose use.

You can still use it in 50 ohm applications but the output amplitude will be reduced to 1/13th or by 22.3dB.  There is nothing wrong with using it without any termination for a higher output voltage.
 

Offline beowulfenator

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Re: WaveTek function generator - unexpected amplitude in MHz range
« Reply #2 on: June 26, 2018, 06:10:21 am »
Thanks! Now all I need to do is to modify it to accept a modern battery type!
 


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