General > General Technical Chat
Review: Hantek DDS 3X25. Anyone own one?
Mechatrommer:
i dont care much about resource leak. terminate the program will terminate the leaks too, i believe its automatically handled in windows. i got software 3.2.1.7 here that i think downloaded from hantek web decompressed correctly, so i'm not sure with your.
while playing with opamp this few days, i got repeatable hanging in the software when i try to change the wave the 2nd time. connecting and reconnecting usb solve this. but then the hang repeat again. i think this is because i'm feeding the buffer opamp thats the 3x25 feeding into, with noisy power supply. my suspect is when noise got into the unit, maybe the fpga will stop responding to usb.
while still in it. from my observation in previous post that the shape of synch signal will be affected by the where the output signal/phase is, there's some sort of cross talk between this 2 lines, maybe this way the noise will be able to sneek in directly to fpga. i think so.
saturation:
I've not yet experienced any lockups or resource issues, but even so, once the Hantek receives its marching orders you can actually set it so it retains the commands and you can log off the client.
I haven't used mecha's software as extensively but its great, and any issues I find, just turning the software off then back on solves it.
Its not elegant, but it happens so infrequently, its the price to pay for a $160 100 MHz FG.
BTW, the thread is long because its has a lot of technical detail. Its probably the most detailed dissection of the 3x25 there online and it was made to give the reader faith that this cheapie can do the job.
Mechatrommer:
hi again. i've made profiling (flatness test) on hantek dds3x25 signal output. its "not so good" method measured with rigol ds1052e (100mhz hacked), open end (unterminated) measurement direct BNC connection from DUT/FG to DSO, max amplitude feed of ±3.5V sine wave from "virtual" pc controller panel. with 50 ohm terminated signal, please expect ~half the value. please note the sine signal will become distorted at 50MHz < freq < 100MHz, rendering the result is less reliable, esp somewhere 70MHz < freq < 100MHz. if you know what i'm talking about. :P so, for what its worth, the picture and the xls file...
saturation:
Thanks mecha for the data. If you're looking to do a VAC vs Hz graph is better to do it terminated with 50 ohms. What you are looking for is a transfer of power to the load, and even if the amplitude is reduced, the power is constant. So the roll off will begin much later; from your graph is looks like if you halve the amplitude, the roll off will begin at 40 MHz.
What you'd like in a signal source is as much flatness throughout the spectrum rather than maximum amplitude. Without termination, at 1.5 Vpp you could get that from 0-100 MHz, which is fairly good. That means all the harmonics generated are also flat, at least to the limits of full frequency response of the source and the capacity of your test gear to see it. After all, the purpose of a FG is not to provide power output, but signal fidelity and wide bandwidth for testing.
For example, in the old analog days video signals are all under 2 Vp.
The limitation of the Hantek is if you were to use it as a test input or clock for 5V logic. But unterminated, you could easily drive it to 20 MHz without the front end op amp you designed and posted on another thread.
Mechatrommer:
--- Quote from: saturation on June 07, 2011, 01:55:10 pm ---If you're looking to do a VAC vs Hz graph is better to do it terminated with 50 ohms. What you are looking for is a transfer of power to the load, and even if the amplitude is reduced, the power is constant. So the roll off will begin much later; from your graph is looks like if you halve the amplitude, the roll off will begin at 40 MHz.
--- End quote ---
a quick report on terminated reading... i told you so, you dont believe me! just halve the volt will ya? ;) and how do we measure power anyway? i dont have gossen metrawatt?! ??? as i said, its not so good, not really accurate, just a rough estimate. cheers!
i try to give raw data here. so later viewer can make the voltage division by themself, be it if they want to terminate it properly with 50ohm, 10ohm, 1Mohm whatever.
--- Quote from: saturation on June 07, 2011, 01:55:10 pm ---and even if the amplitude is reduced, the power is constant
--- End quote ---
sorry i'm not following this... how come the power is constant if the voltage is reduced?
if V is halved, so do I. so P should be quarter, not constant? ???
P = (I/2)^2 . R
P = I^2.R / 4
P is the function of I, and I is the function of V. how come P is constant if V is changed?
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