Poll

What is your interest in the Hantek DDS 3x25?

I own one
36 (27.1%)
I am considering getting one
40 (30.1%)
Curious about the hack
16 (12%)
Just passing through
41 (30.8%)

Total Members Voted: 111

Author Topic: Review: Hantek DDS 3X25. Anyone own one?  (Read 289871 times)

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Offline torch

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Re: Review: Hantek DDS 3X25. Anyone own one?
« Reply #450 on: January 07, 2013, 03:51:02 am »
I know Mechatrommer built an amplifier to get 10v out of his, but does anyone know the minimum voltage the Hantek can reliably produce?

I'm restoring an old (1939) tube powered floor model BC and SW radio. To align the tuner, the manufacturer's instructions say to connect a signal generator to the antenna input. Required frequencies range from 655KHz to 17MHz. I figure the AM waveform on the Hantek is perfect. However, I'm concerned about the output voltage. Near as I can figure it, a weak signal would produce around 0.2uV and a strong signal around 50uV at the antenna connection (I believe it's approximately 50 ohm impedance). The lowest setting on my Rigol scope is 2mV/div, so I can't verify if the Hantek can operate at that level. It does seem to still be working at 1mV, but even that is hard to see.

Option B would seem to be installing a 10K resistor inline. If this was a DC (or at least, low frequency) circuit and if the input impedance was resistive, I think the load and resistor would form a voltage divider so 1mV from the Hantek would produce 5uV (a reasonably strong, but not overwhelming signal) at the antenna. But I have no idea if that would really work at 17MHz.

Option C would be to install a short piece of wire as an antenna on each and let the Hantek broadcast to the radio by laying the wires next to each other. But that seems even more random.

Any other options?
 

Offline SeanB

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Re: Review: Hantek DDS 3X25. Anyone own one?
« Reply #451 on: January 07, 2013, 04:40:11 am »
Normally you couple by using a single turn of wire draped over the IF transformer, with it twisted pair to the signal generator. This normally couples enough in to use for alignment. This works to align the IF stages, for the RF side just hold the loop over the antenna input.
 

Offline Mechatrommer

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Re: Review: Hantek DDS 3X25. Anyone own one?
« Reply #452 on: January 07, 2013, 10:33:23 am »
i havent done this but if its me i'll set the signal magnitude to max (6Vpp or 20Vpp doesnt matter) and attenuate it at the output end accordingly using simple voltage divider or other better mean. the rational is so you can get minimal stairsteps effect. my 10x25 amplifier is not suitable for this application imho as it may introduces more distortion to the original output in opamp stage. use the original output as is. since its iirc 12bit @ 6Vpp you may expect 1.46mV stairsteps out of it. attenuating the signal should attenuates the stairsteps as well. but be careful with your attenuator design as it is near dark region (20MHz) this thing has made me crazy and probably brain shorted for a while now. a resistor is not a resistor, it also an inductor and capacitor, add pcb ground somemore? they will dance make you nuts.
Nature: Evolution and the Illusion of Randomness (Stephen L. Talbott): Its now indisputable that... organisms “expertise” contextualizes its genome, and its nonsense to say that these powers are under the control of the genome being contextualized - Barbara McClintock
 

Offline zibadun

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Review: Hantek DDS 3X25. Anyone own one?
« Reply #453 on: January 08, 2013, 05:00:11 pm »
Yes I agree the lower the output the higher is harmonics content (relative to main carrier). At 0.1 V the sine wave is hardly a sine anymore. An attenuator or loose coupling is the way to go :)
 

Offline jahonen

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Re: Review: Hantek DDS 3X25. Anyone own one?
« Reply #454 on: January 08, 2013, 09:00:04 pm »
Why not just get a coaxial attenuator, fixed ones should not be too expensive? You can also cascade them to get desired attenuation if one is not enough.

Regards,
Janne
 

Offline robrenz

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Re: Review: Hantek DDS 3X25. Anyone own one?
« Reply #455 on: January 08, 2013, 09:16:25 pm »
Why not just get a coaxial attenuator, fixed ones should not be too expensive? You can also cascade them to get desired attenuation if one is not enough.

Regards,
Janne

Is there something in the internal design of a coaxial attenuator other than the shielding effect of the outer shell being grounded that makes it better than an equivalent non inductive resistive divider with proper shielding?

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Re: Review: Hantek DDS 3X25. Anyone own one?
« Reply #456 on: January 08, 2013, 10:04:57 pm »
A well designed attenuator will maintain a 50 ohm impedance throughout, a loose resistor will most likely cause an impedance mismatch, with the usual signal degradation and loss.
 

Offline torch

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Re: Review: Hantek DDS 3X25. Anyone own one?
« Reply #457 on: January 09, 2013, 12:24:08 am »
I did some testing of resistor voltage dividers, with a 50 ohm audio transformer standing in for the antenna input transformer. As you guys warned, the signal was badly distorted.

Two pieces of wire placed side by side resulted in a fairly decent attenuated coupling. Reversing one piece of wire inverted the signal, but that shouldn't matter.
 

Offline Mechatrommer

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Re: Review: Hantek DDS 3X25. Anyone own one?
« Reply #458 on: January 09, 2013, 02:45:31 am »
Is there something in the internal design of a coaxial attenuator other than the shielding effect of the outer shell being grounded that makes it better than an equivalent non inductive resistive divider with proper shielding?
i believe you missed the attenuator construction i teared down recently and some usefull link(s). this is china cheapo one. if you can lay better and uniform carbon layer and then verify its profile then thats a good engineering ;) here the teardown https://www.eevblog.com/forum/beginners/replace-carbon-layer-with-passive-resistors-components-in-attenuator with 1 concise and reasonable answer why not to use normal resistors.
Nature: Evolution and the Illusion of Randomness (Stephen L. Talbott): Its now indisputable that... organisms “expertise” contextualizes its genome, and its nonsense to say that these powers are under the control of the genome being contextualized - Barbara McClintock
 

Offline torch

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Re: Review: Hantek DDS 3X25. Anyone own one?
« Reply #459 on: January 13, 2013, 05:25:53 am »
I am aligning a short wave radio and need an audible tone AM modulated on a carrier -- from around 9MHz to 17MHz. So I figure a 1000:1 ratio should be fine, giving me a 17KHz tone at the upper end.

In ArbExpress, I generated an arbitrary waveform using the expression

Sin(1000*w)*(1+0.75*Cos(1*w))

to generate 1000 sine waves, the peaks of which form one overall sine wave. Zooming in on the waveform within ArbExpress confirms the waveform is as expected:



When I load it into the DDS3x25 via Goltek, the overall shape appears correct (goltek set to 20 hz):



However, zooming in a bit, something doesn't look right -- instead of sine waves, it appears to be an underlying modulated wave:



Zooming in further confirms this. I do have the right number of pulses, but they ain't sine waves, They are groups of square waves that gradually average out into the overall shape:



I'm not entirely sure what is going on here:



I suspect those random drop-out glitches are something to do with the Rigol and timing. If I zoom out still further the waveforms appear fine again. It only happens at that one setting.

Is this some sort of glitch with Goltek or with the Hantek? Or am I doing something completely wrong?
« Last Edit: January 13, 2013, 05:43:24 am by torch »
 

Offline torch

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Re: Review: Hantek DDS 3X25. Anyone own one?
« Reply #460 on: January 13, 2013, 06:01:06 pm »
I got it working -- sort of. Not really a sine wave, and a bit jittery, but I think it will be accepted by an old tube radio:



The superimposed audio frequency sine wave has similarly jittery amplitude, but should work nonetheless:



So it will work at 17KHz (for an RF of 17MHz)

However, I still have the original problem at 15.26KHz, which I need for aligning the 15,260KC point.
« Last Edit: January 13, 2013, 06:04:31 pm by torch »
 

Offline zibadun

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Re: Review: Hantek DDS 3X25. Anyone own one?
« Reply #461 on: January 13, 2013, 06:05:44 pm »
nice work. for some reason I could not get Arb Express to generate anything for me.  I select Basic Waveform/Sine, 40MHz and all I get  is a flat line. :(
 

Offline Mechatrommer

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Re: Review: Hantek DDS 3X25. Anyone own one?
« Reply #462 on: January 13, 2013, 06:18:48 pm »
ok i saw your csv file that you emailed me. the problem...

"instead of sine waves, it appears to be an underlying modulated wave"
due to aliasing resulted from downsampling made by goltek from unsupported 10,000 pts to 2048 pts which is the managable value by 3x25

"They are groups of square waves that gradually average out into the overall shape"
due to you are asking 3x25 to run at very slow sampling rate (40KSps). coupled with the kind of downsampled points will generate that very bad (worst) stairsteps, its the nature of DAC inside the 3x25.

"I suspect those random drop-out glitches are something to do with the Rigol and timing"
did you activate peak detect mode? if not then this is common problem with discrete sampling DSO... signal aliasing, is when the dso is sampling at the rate less than 2 times of the signal frequency. thats why Mr Shannon worked hard on this and produced his theory long time ago.

hint 1...
refer to gui.png, for optimum result, make csv that has the same number of points as shown in the gui, other than that goltek will interpolate (upsampling) or select few points from the whole (downsampling). the number of points is not something that we can choose as we like, it is specified by the device/api, the value is returned from function call (the calculation is based on marmad's KSps formulation) and that is used by goltek to make the interpolation. so if you expect goltek to do the interpolation, probably something bad can happen (disclaimer: i will not held liable for any property or life damage ;)) such as highly distorted or aliased signal.


hint 2...
for those of you who dont know... square and sawtooth buttons in goltek use different interpolation method, ie nearest neighboor interpolation, specifically made for sudden cliff like signal (you can load arb data to those buttons as well, but be carefull to save or keep your original square and sawtooth file in case you want to reload the original) ie when the data got 2 consecutive points inside it that go from lowest to highest and you want to preserve it in interpolated data. not like other button which use linear calculation to create NEW points. for eq if we have 2 points valued 0 and 1, we want to upsample to 4 points. square or sawtooth button will interpolate it to 0011, but other signal buttons will interpolate it to 0,0.333,0.667,1 not a good idea for square wave like or high pulse signal.

hint3...
to investigate what kind of data that is produced (interpolated or downsampled) and sent to 3x25 by goltek, you can right click on the graph picture -> dump -> hantek volt data. goltek will produces a file inside its directory "volt.dump.csv" (make sure you dont lock this file if already exists while dumping, nasty unspecified thing can happen) i've attached the sample below (volt.dump.zip) which is downsampled from torch's original data.

using hint1, i tried to produce 2048 data based on torch's formula in excel (attached modulation2048.xls zipped) but guess what? this intermodulation is also there! so whether goltek interpolation or using theoritical formula, its still the same, pay attention to the data shown in gui.png (Ksps and number of points) and make your own calculation and senses, beyond that i cant help much, we are live in discrete sampling world now.

in compare.png, i plotted first 30 points of what is produced and sent by goltek interpolation (left) and compared to the same data count/set using math (right), the result are about the same, those sharp peaks (pointing up and inverted) represent each point, top and down consequtively. when sent to 3x25 at finite sampling rate you'll get the malevolent stairsteps. let me re-view it again here.





FWIW.
Regards,
Shafri.
« Last Edit: January 13, 2013, 07:24:40 pm by Mechatrommer »
Nature: Evolution and the Illusion of Randomness (Stephen L. Talbott): Its now indisputable that... organisms “expertise” contextualizes its genome, and its nonsense to say that these powers are under the control of the genome being contextualized - Barbara McClintock
 

Offline torch

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Re: Review: Hantek DDS 3X25. Anyone own one?
« Reply #463 on: January 13, 2013, 09:09:11 pm »
Well that certainly explains a few things. I didn't realize there was a 2048 point limit. I thought as long as it was within the sample rate at a given frequency, I would be OK.

Getting a usable waveform at 17KHz was basically dumb luck and the jitter was an artifact of the interpolation process. But that does suggest it is possible to get something usable at 15.26KHz, given the right combination. I quickly tried 2048 points, but as one might expect, the "audio" component was over 75KHz -- well beyond my range of hearing. If I can figure out a way to get ArbExpress to use trianglular instead of sine waves I could get away with 2 points per wave, dropping the audio to 15KHz or so. Even I should be able to hear that.  Otherwise I guess I'll just have to fiddle around and try to find the right combination.

I realize there is no warranty, express or implied, on Goltek or it's fitness for a given purpose. ;-) But I appreciate your time and help and thank you for it.

 

Offline Mechatrommer

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Re: Review: Hantek DDS 3X25. Anyone own one?
« Reply #464 on: January 13, 2013, 11:23:11 pm »
I didn't realize there was a 2048 point limit.
marmad has made extensive study on this. the max points 3x25 can accept is 4096, but its by luck at certain freq and/or KSps config to get that, mostly 3x25 will use 2048 points. me myself have not figure out the combination. i'll need to dig this up if i need to, its somewhere here or in my HDD. please check your PM will ya? ;)
Nature: Evolution and the Illusion of Randomness (Stephen L. Talbott): Its now indisputable that... organisms “expertise” contextualizes its genome, and its nonsense to say that these powers are under the control of the genome being contextualized - Barbara McClintock
 

Offline torch

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Re: Review: Hantek DDS 3X25. Anyone own one?
« Reply #465 on: January 14, 2013, 01:35:52 am »
Sorry for the delay. PM sent.
 

Offline Mechatrommer

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Re: Review: Hantek DDS 3X25. Anyone own one?
« Reply #466 on: January 14, 2013, 01:42:46 pm »
this is the PM from torch that i asked. let me just quote here for educational purpose, others might benefit FWIW...
"The alignment (carrier) frequencies are 9.5 MHz, 11.8 MHz, 15.26MHz, and 17 MHz. The modulated signal frequency can be any tone in the range of human hearing. Anything between 5 KHz and 17 KHz would work"

there are two workarounds to take full advantage of goltek feature to get the best result out of it, not "the best in this world" result but "the best it can produce" result. please put your Shannon-Fanno's hat on and the magic wand (pencil) first... ready? here we go!

workaround 1:

now, we manually create the 4096 points in csv, you may use your programming or typing skill whichever you prefer (i used ms excel + notepad). we use 2 points for each cycle of the carrier signal and 4096 points for each cycle of the modulated signal, and superimpose them in the 4096 data. refer to "am_modulation w + 2048w.xls" in "4096pts 2048+1 modulation.zip" we will get 2048 cycles of carrier and 1 cycle for signal. set the #SIZE parm to 4096, done?! not yet! now we set the #CLOCK parm...

case:
1) 9.5MHz carrier, set #CLOCK=19e+06. calculating from master formula (in gui.png above) we'll get modulated 19MSps / 4096 = 4.6KHz, thats our audiable signal, fine, next...
2) 11.8MHz carrier, set #CLOCK=23.6e+06. calculating from master formula (in gui.png above) we'll get modulated 23.6MSps / 4096 = 5.8KHz, thats our audiable signal, fine, next...
3) 15.26MHz carrier, set #CLOCK to 2x of carrier freq like 2 cases above, so=30.52e+06. 7.5KHz audio, next...
4) 17MHz carrier, same as above #CLOCK=34e+06. 8.3KHz audio, done!

same dataset, same datacount, the only difference is the #CLOCK value. save as csv (ArbExpress compatible) and load to goltek Arb Button. setting in utility...
force clock on
signal boost off
flatness control off

hit the usb button (sending signal to 3x25) you'll get your modulated signal, easy? no, it comes at a price. since 3x25 is budget stuff we dont expect miracle, it cannot produce exactly the sample rate we provided (#CLOCK) ie 19MSps will be rounded off to 20MSps, 23.6MSps to 25MSps, 30.52MSps and 34MSps to 33.333MSps, so practically we'll get a signal that is a little bit off the intended signal, no luxury there its the limitation of the hardware. so the true output will be...

case:
1) 20MSps. 10MHz carrier + 4.9KHz audio. our intention was 9.5MHz carrier + 4.6KHz audio
2) 25MSps. 12.5MHz carrier + 6.1KHz audio. our intention was 11.8MHz carrier + 5.8KHz audio
3) 33.333MSps. 16.67MHz carrier + 8.1KHz audio. our intention was 15.26MHz carrier + 7.5KHz audio
4) same as 3. our intention was 17MHz carrier + 8.3KHz audio.

so the drawback. it will be out of alignment by some magnitude.

workaround 2:

now, we manually create the 4096 points in csv like above, but this time we base our calculation from the clock rate that 3x25 can produce. lets say for example case 1. we use math formula to fit the data with the carrier signal, instead of 2 points per cycle we'll use 20MSps / 9.5MHz = 2.105263158 points per cycle nice number! so in the 4096 points data, we will have 4096 / 2.105263158 = 1945.6 cycles nice number again! i wont explain further i assume you got the idea, example file is in "4096pts 1945.6+1 modulation.zip" the problem? as i've mentioned in earlier post, math formula itself created aliasing in the signal, just like what torch demo previously. so this workaround #2 may works for other application but not this modulation application (aliasing creates additional intermodulation). i just explained it here for completeness.

ps: the attached files are for Windows format (line feed + carrier return CHR(13)+CHR(10)) if they dont work for your OS, be pleased to inform me i can convert them to Unix or Mac format.

i provided the 3x25 output when loaded with "17MHz+8.3KHz.csv" and "9.5MHz+4.9KHz (real).csv" so you can see and examine for yourself... i suspect on higher end higher BW DSO, the 17MHz 16.67MHz carrier will resembles more like the nasty stairsteps that torch demo in earlier post, except the DAC is running at 33.333MHz clock instead of 40KHz as torch commanded.
« Last Edit: January 14, 2013, 01:55:44 pm by Mechatrommer »
Nature: Evolution and the Illusion of Randomness (Stephen L. Talbott): Its now indisputable that... organisms “expertise” contextualizes its genome, and its nonsense to say that these powers are under the control of the genome being contextualized - Barbara McClintock
 

Offline torch

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Re: Review: Hantek DDS 3X25. Anyone own one?
« Reply #467 on: January 14, 2013, 06:05:04 pm »
Quote from: Mechatrommer
using hint1, i tried to produce 2048 data based on torch's formula in excel (attached modulation2048.xls zipped) but guess what? this intermodulation is also there! so whether goltek interpolation or using theoritical formula, its still the same, pay attention to the data shown in gui.png (Ksps and number of points) and make your own calculation and senses, beyond that i cant help much, we are live in discrete sampling world now.


I reconfigured ArbExpress for 2048 points (leaving all the other parameters the same) and it produced the same double-modulated waveform. So I would say the Goltek algorithm also agrees with Tectronix.

I'll have to re-read your latest a couple of times to absorb all the details, but I think I understand the gist of it. Thanks for your help!
 

Offline torch

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Re: Review: Hantek DDS 3X25. Anyone own one?
« Reply #468 on: January 20, 2013, 04:42:43 pm »
I have poured through Mechatrommer's files and explanations and while there are still some aspects I don't fully understand, most of it makes sense. As others have said, this is a very versatile piece of equipment for the money, but it is a fairly cheap piece of equipment and has more limitations compared to expensive professional grade equipment. 

What I am trying to do just can't be done with 2048 data points. Mecha's examples at other frequencies do generate a decent signal, but unfortunately those frequencies are too far away from what I need. For example, the 19 meter shortwave band only spans 15.10 to 15.60 MHz, so 16.67 MHz just won't work as an alignment signal.

The long and the short of it is that the DDS 3x25 generates a good AM moduated wave at medium-wave frequency, a perfect SW carrier wave or a perfect audio wave, but just cannot produce a good AM modullated wave at all SW frequencies. Time for another solution. I was sitting there staring at things when my eye caught the headphone output jack on the small laptop I use to run Goltek. Now, the sound card can't generate a SW carrier, but is great at audio frequencies. If I could combine the two, I could let the Hantek do what it does best and let the laptop handle the audio. I didn't have a suitable audio transformer at hand, so this is what I came up with (modified from a schematic I found on the internet):



It only has one NPN transistor so it actually only produces a half-wave:



And the carrier, while nearly perfect on the breadboard ended up a little distorted when soldered together, but it's at the right frequency and seems close enough for the tubes:



It fits in a tiny project box. I cut the cable off an old set of earbuds for the audio feed, scavenged a wall-wart for the power supply with an in-line DC jack cut off another cable previously scavenged for another project:



Good thing it's a large floor model radio with a large, flat top! For the audio signal, I d/l a freeware program from http://www.dr-jordan-design.de/signalgen.htm. The combination generates a clear loud tone at the desired frequency with little to no cross-over. Perfect for what I needed to do. I set the tone at 800Hz and can quickly type a new carrier frequency into Goltek as I flip back and forth between the bands for the various adjustments






 

Offline Mechatrommer

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Re: Review: Hantek DDS 3X25. Anyone own one?
« Reply #469 on: January 20, 2013, 04:59:33 pm »
congratulation torch! just make sure it doesnt catch fire :P. i agree the 3x25 is very versatile, a lot of things we can learn from it. its cheap but generic, sure it cannot do specific thing like RF-gen or syntethizer etc, but we can always rig up specific circuit for our need at the output, made me appreciate the higher end gears stuffs and learnt a little bit knowledge and "how do they work" of them.
Nature: Evolution and the Illusion of Randomness (Stephen L. Talbott): Its now indisputable that... organisms “expertise” contextualizes its genome, and its nonsense to say that these powers are under the control of the genome being contextualized - Barbara McClintock
 

Offline torch

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Re: Review: Hantek DDS 3X25. Anyone own one?
« Reply #470 on: January 20, 2013, 08:22:34 pm »
just make sure it doesnt catch fire :P.

Well at least that would be something I'm qualified to deal with!   (I can also handle the situation if the circuit has a heart attack, falls half-way down a cliff, spews methl-ethyl nasty into the watershed or goes into premature labour.) Until then, I'll have to continue calling on you guys for advice and assistance because I really don't know what I'm doing with these things.
 

Offline SeanB

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Re: Review: Hantek DDS 3X25. Anyone own one?
« Reply #471 on: January 20, 2013, 08:25:03 pm »
Physician, heal thyself........
 

Offline davyk

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Re: Review: Hantek DDS 3X25. Anyone own one?
« Reply #472 on: February 04, 2013, 06:20:56 pm »
Hi,
Can anyone (or you dear OP) inform me where I can find the link to the software ?

Regards,
vYk
Kind regards,

vYk
 

Offline torch

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Re: Review: Hantek DDS 3X25. Anyone own one?
« Reply #473 on: February 04, 2013, 07:48:36 pm »
Mechatrommer's Goltek? http://soasystem.com/eng/goltek/
 

Offline davyk

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Re: Review: Hantek DDS 3X25. Anyone own one?
« Reply #474 on: February 04, 2013, 10:42:22 pm »
many thanks torch, VERY fast answer !!!
I'm gonna try this.
was the link in some post in this topic?

Regards,
vYk
Kind regards,

vYk
 


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