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Review: Hantek DDS 3X25. Anyone own one?

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Mechatrommer:
well, whats the purpose of the last one?

saturation:
Its one piece and since its straight, it may do better in highest frequencies.  For high frequencies you need to avoid sharp 90 deg bends in any conductors [like the T connector], it can induce capacitances that can alter Zo, but practically speaking I think you can use T or Y adapters to over 300 MHz.

See under 'routing'.  
http://www.icd.com.au/articles/emc.html

For more info a google search term is signal integrity. For one reference that has everything, see 'High Speed Digital Design.'






--- Quote from: Mechatrommer on March 15, 2011, 04:06:23 pm ---well, whats the purpose of the last one?

--- End quote ---

saturation:


I presume this is trapezoid waveform, yellow, and blue is sync signal.  Not sure which frequency used, so my screen captures are for 12.5 z.

The FFT is to show that the harmonics present in the waveform is to confirm its trapezoidal, not sine as they look very similar.  My mistake, your previous images with the harmonics explains that.  I'll correct my reply.

alm:

--- Quote from: saturation on March 15, 2011, 03:13:08 pm ---50 ohm resistor of unknown composition, I hope its not carbon composite or wire wound, its not the ideal terminator.

--- End quote ---
What's wrong with carbon composition for this purpose? Before alternatives like thin film came around, this was actually the resistor of choice for high-frequency work. Wire wound can be OK if it's wound with an Aryton-Perry winding (cancels most of the inductance), otherwise it's obviously horrible. Even the extra ~10nH of a carbon/metal film resistor shouldn't be an issue, and I wouldn't expect major issues with 50/75 ohm mismatch either. I agree with your other points, though, and in my opinion this setup looks more suitable for connecting a light bulb than a high(ish) frequency signal. This is not DC or audio (which is basically the same), you can't just splice two wires together and expect good signal integrity.

saturation:
Mecha has found a new bug in the 3x25. I think I understand now what he was saying by 'multiple' and 'leap year trick'.   I had time to duplicate some of his tests and he discovered a new problem with the sync signal.  Its exactly what he describes but I couldn't understand what his metaphor was.

Its part of dajones original complaint that isn't solved completely by fixing the impedance.

At certain frequencies the sync and the Voutput remain unsynchronized!  There are however, frequencies that you can synchronize but this bug can certainly throw people off.  This is was mecha was referring as 'multiple'.  In between certain values the sync signal and the output signal are not identical, so you cannot sync both waveforms until you reach the 'multiple'.

This doesn't affect Vout, but it does affect using the sync signal to lock in Vout, if you choose.

That's why he couldn't sync at 12MHz but I can at 12.5 MHz.



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