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RD JDS6600 25MHz 2-Channel DDS AW Function Signal Generator
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vk2seb:

--- Quote from: technogeeky ---Hopefully we'll see a basic teardown soon.
--- End quote ---

Here are some high-resolution images that I took of the main boards from my (brief) teardown in the video above:

Top of the main board:


Base of the screen board:


Bottom of the main board (nothing interesting)
vk2seb:

--- Quote from: Kleinstein ---An FPGA and R2R ladder DAC is rather common for the low cost Fgens.

--- End quote ---
Interesting, I've haven't torn down a cheapie Fgen like this before so that explains that.

--- Quote from: Kleinstein ---I would consider 4 points for further tests:

--- End quote ---

Cheers for the suggestions!


--- Quote from: Kleinstein ---1) Noise, e.g. from the SMPS or just from the DAC: So maybe use just a DC or low amplitude sine.

--- End quote ---

DC out at 1V, AC coupled, output OFF:



Same as above, output ON:




--- Quote from: Kleinstein ---2) DAC linearity: This can usually be seen from a slow triangle / ramp.

--- End quote ---

Triangle wave, 1KHz, 1Vpp:




--- Quote from: Kleinstein ---3) Output amplifier slew rate: Many similar low cost generator run in to a slew rate limit with full amplitude and high frequency. So usually the maximum amplitude is reduces at the highers frequency.

--- End quote ---

Here's a sine wave, 25MHz, set to 1Vpp (but into a 50 Ohm load so what we 'should' see is 500mVpp)



Same as above, but a square wave:




--- Quote from: Kleinstein ---4) There are 2 relays per output channel. So this could be an output attenuator. This has good sides, but might also limit the Offset range, when using low amplitudes.

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Looks like you were right about the output attenuators, at 100mVpp setting (into 50 Ohms again), the maximum offset I can set is 0.25V;

gedong:
I Actually just find out this today while searching for budged DDS gen..

actually they look almost identical..


One of reviewer said that this model uses Altera FPGA Cyclone IV, but never showed the internal boards..
gby:
The JDS6600 generator family has very similar functionality to the Feeltech FY3200 and the MHS-5200 generators.  The JDS6600 even uses the exact same plastic case for the enclosure as the FY3200, MHS-5200.  For a comparison of those other generators see:
https://www.eevblog.com/forum/testgear/feeltech-fy3224s-24mhz-2-channel-dds-aw-function-signal-generator/msg697718/#msg697718

From testing the FY3200 myself and reading on the MHS5200 they both are both limited in their output voltage range into 50 Ohm load without clipping or high distortion.  So the first test I would suggest is:

  1.  Set 10 KHz sinewave with 20 Vpp/maximum amplitude on an oscilloscope with 1 Meg impedance.  Then add the 50 Ohm termination and see if the output drops to 1/2 or if clipping or distortion starts happening.

On these type generators the output buffer is often slew rate limited which in turn means the output amplitude at higher frequencies is limited.  So, the second test I recommend is:

  2.  Set a 10 Vpp 100 kHz sinewave on the output into oscilloscope with 50 Ohm termination.  Then increase the frequency until maximum frequency to see if or at what frequency it starts distorting horribly.

On the FY3200 generator when you change the frequency the output waveform glitches.  Ideally one would expect a change in frequency with a sine wave to step change the slope at the frequency change with no step in the actual voltage.  Unfortunately the FY3200 has steps in the output because the phase as well as the frequency changes when you change the frequency.  So, the third test I would love to see is:

  3.  Set the generator to 5 Vpp, 10 kHz sine wave and then step change the frequency to 20 kHz.  Try to capture on the oscilloscope the moment when the frequency changes.  If you have advanced triggering I set trigger width must be < 20 uSec and then set to capture once.

When you use two channels both outputting the same frequency sine wave with the phase 90 Deg apart it would be great to repeat test 3 to insure that both channels change frequency at the same time and with no glitches.

  4.  Repeat test 3 but with two sine wave channels outputting sine waves with 90 Deg relative phase.

The last requested test is really just a question of functionality.  This generator can do frequency sweeps.  But, can it do frequency sweeps while outputting two wave forms?  Last requested test is:

  5.  Can you set the generator to output 2 sine waves with 90 Deg relative phase and then sweep the frequency such that both channels sweep in frequency and stay in phase lock?

In advance I thank you for any of the above tests that you could do and report back results.
Kleinstein:
The triangle waveform looks quite good - better than I remember from the MHS5200. However the scope setting is not that good to tell if the little nonlinearity is from the scope of from the generator. If would need a zoom in on details of the slope and maybe an even lower frequency. Usually a simple R2R DAC would show visible errors near the center or 1/4 of the range. There are 2 pots for each channel so these might be for adjusting at least that largest error.

The picture of the circuit is just to bad in resolution to read the chip numbers. The output amplifiers might be interesting. For the rest I would expect an AD603 or similar for the amplitude adjustment.

Are the USB and TTL I/Os isolated from the normal outputs ? It does not look like.
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