General > General Technical Chat

Review: Hantek DDS 3X25. Anyone own one?

<< < (67/108) > >>

Mechatrommer:
i've made some simple note while i'm at it. FWIW. DDS3X25 as Digital Generator

saturation:
Nice!  Thanks for that mecha. 


--- Quote from: Mechatrommer on October 22, 2011, 07:57:54 pm ---i've made some simple note while i'm at it. FWIW. DDS3X25 as Digital Generator


--- End quote ---

Tectonic:
You can add me to the list of 3x25 owners. Praises to you Mechatrommer, for your GolTek Controller. Also thanks to all the helpful contributions from other members.

So far the 3x25 is exceeding all my expectations. I've been searching for a decent function generator to play with while I'm learning Robotics and this is a true gem in its price range. I searched for affordable used bench top models as well as new devices at entry level pricing. This proved to be more complicated than I had anticipated by a few orders of magnitude!

I do have a few questions for you guys in regards to the signal output I see on my scope. The first Picture is of a 5MHz square wave. Output impedance from the GolTek Controller is set to 50ohm. The oscilloscope is an 400MHz analog Tektronix 2465B calibrated about 3 years ago.





This second picture is of the same square 5MHz wave. This time I'm using a P6139A probe connected to a Pomona BNC to minigrabber test clip, which is plugged in directly to the 3x25. Impedance is still set to 50ohm.




And now the same signal using the probe but reducing impedance to 1ohm.











In the first picture, what I think I'm seeing is over input impedance. I believe I'm seeing something similar to what's noted in Linear Technology's AN47-14 (pdf). The third picture using the probe and the impedance set to 1ohm also shows the curve at the top of the rising edge and bottom of the fall.

If this is indeed caused by over input impedance, is there a way to compensate even further via software? Also of note is the amount of ringing.

alm:

--- Quote from: Tectonic on November 24, 2011, 07:17:21 pm ---I do have a few questions for you guys in regards to the signal output I see on my scope. The first Picture is of a 5MHz square wave. Output impedance from the GolTek Controller is set to 50ohm. The oscilloscope is an 400MHz analog Tektronix 2465B calibrated about 3 years ago.

--- End quote ---
Rise time of about 5ns, seems reasonable (not sure what the rise time spec is). Is the scope set to 1 Mohm or 50 ohm? A 50 ohm input impedance should give the best performance. The impedance setting in the generator will probably only change the amplitude calibration. Eg. if the output impedance is 50 ohm, you expect half the amplitude with 50 ohm load, and the full amplitude with 1 Mohm load.


--- Quote from: Tectonic on November 24, 2011, 07:17:21 pm ---This second picture is of the same square 5MHz wave. This time I'm using a P6139A probe connected to a Pomona BNC to minigrabber test clip, which is plugged in directly to the 3x25. Impedance is still set to 50ohm.

--- End quote ---
I wouldn't expect a great signal when using some flying leads, I would only use coaxial connections. If you don't have a probe tip to BNC adapter, try putting the probe tip directly in the BNC socket and make a short ground connection (not the alligator clip) between the probe sleeve (unscrew the plastic part) and BNC shell. Twisting a cut off resistor lead around the ground sleeve might work. The less inductance, the better.


--- Quote from: Tectonic on November 24, 2011, 07:17:21 pm ---And now the same signal using the probe but reducing impedance to 1ohm.

--- End quote ---
Reducing impedance to 1 ohm? You mean putting a 1 ohm resistor in parallel with the probe? Or some setting in the software?

Tectonic:
With the BNC cable, the scope is set to 50ohm. With the probe the scope is at 1Mohm. I reduced it to 1ohm via software.

Edit: The adapter was the problem as you suggested. I used the probe directly on the 3x25 and the wave looks similar to the one I get in the first picture with the BNC cable.

Navigation

[0] Message Index

[#] Next page

[*] Previous page

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod