General > General Technical Chat

Review: Hantek DDS 3X25. Anyone own one?

<< < (19/108) > >>

saturation:
Hi alm,

I've never really experimented with using carbon composite for anything above 1 MHz. I should give that a whirl and report back if I still composites around.  Heard of a type of induction canceling resistor that must have been it, but I've never seen one:  
http://en.wikipedia.org/wiki/Ayrton-Perry_winding

When composite was popular, I'd suspect 'high frequency ' was at a lower range compared to today.  

In mecha's tests, given harmonics of the waveform used, and the sensitivity of the sync to output impedance, I'd strongly suspect cabling plays a bigger role in the waveforms appearance but the 3x25 design flaws are responsible for the lack of synchronization. Viewing each channel using a different trigger and the right impedance produces a relatively clean waveform, see another post.

http://books.google.com/books?id=zpTnMsiUkmwC&pg=PA2&lpg=PA2&dq=carbon+composition+resistor+frequencies&source=bl&ots=B4EZgRvC7Y&sig=qJiDRN3VxUrlkxH2Rb2aQ5kBtLU&hl=en&ei=PASATfuTEsSM0QGujIX7Dw&sa=X&oi=book_result&ct=result&resnum=10&ved=0CFgQ6AEwCQ#v=onepage&q=carbon%20composition%20resistor%20frequencies&f=false



--- Quote from: alm on March 15, 2011, 11:09:47 pm ---
--- 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.

--- End quote ---

Mechatrommer:
yes it was dajones try to highlight it in not so comprehensive report/post. i'm yet to figure out whats the basic 'multiple' of this to get "synh out" and "signal" synchronized. and for my non ideal cabling, i think at the same time it will prove how sensitive and stable the 3x25 to any slight impedance mismatch or imperfection in the circuit design. i still highly suspect its the software issue, but then to re-open and check how the hardware perform is my next "to do" list. but the easiest so far i think is to find this "basic multiple" so to work the 3x25 reliably with "synch out" port as if it turn out that this is a software issue, i still incapable to access/mod the spartan (big) chip.

recap...

--- Quote from: DaJones on January 20, 2011, 09:30:49 pm ---
--- Quote ---The Hantek DDS 3x25 is a solid function generator with arbitrary waveform capability, far better in performance than most analog function generators, in its price range or with similar specifications.  It one of the lowest cost 25 MHz capable DDS function generator on the market, and likely the only one with AWG capability.
--- End quote ---
Man, I don't understand how you can say that!
The thing glitches like crazy for square waves above 2.5mhz ( except a few stable spots like 10mhz ).
The sync out line has no timing relationship to the output signal except at those rare "stable" spots.
The sync out line glitches every 20us ( 50khz ) and will glitch any output waveform other than sine waves.
I could NEVER recommend this to anyone, except maybe as a source of sine waves, and as long as you
didn't need to use the sync out line at all.
If you did your stability test at one of the "stable" spots ( like 10mhz ) you might want to try it again at 10.1mhz.

--- End quote ---

Xilinx DS529 Spartan-3A FPGA Family Data Sheet
made a quick view, synch out is from IO_L01P_0 (pin 110). but what the hell, FPGA knowledge is not within my reach :( :P

Mechatrommer:
i run a program to get the LCM... not found! ah sux! you have to chart the 'in synch' frequency manually, there is no 'multiple' anymore. and i tried to look at the 'leap year' effect using pulse trigger, they seem to occur at regular or constant interval, though i need to crank up the timescale and look carefully at those many small oscillation to see 2 consecutive 'leap year' or 'out of synch' as dajones highlighted as in his picture below. so i still highly suspect this is software issue or vhdl or verilog or whatever it is :P



though, 'in synch' seem to be reliable up to 2MHz regardless of any frequency you are putting in, eg 1.3, 1.8MHz etc, but jitter seem to worsen at some odd numbers.

Mechatrommer:
here i present a steady display of:
1) 'leap year' effect @ 1.981 MHz
2) 'dajones out of synch' glitch @ 2.3 MHz
(note: unterminated synch out again :P)

saturation:
A comparison of effects of better cables on the waveform you have demo'd.
Some of instability has relation to the quality of the connections, but its not as big a contributor as the Hantek software bug.  Using persistence mode.  Most striking is a negative glitch is half the magnitude.

Mecha's 10 MHz.



Saturations 10 MHz.

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