DDS 20 Function Generator Kit

[Gregi]

@Thedane:
Supplier confirmed that those bridges are normal and need to be there.

Here is their response in german:

"anbei erhalten Sie die Bau-und Bedienungsanleitung zum DDS20.
IC 5 ist korrekt beschaltet! Pin 2,3 und Pin 10,11,12,13 sind gebr?ckt."

Greg

[gaspo100]

You can look at the noise at various frequencies by refering to the spec sheet for the AD9833.
Its very low level and can be filtered out using some inductors and capacitors.
The output on the scope for the DDS 20 (based on the AD9835) is perfect.

Rob,

I have built several DDS generators with AD9833 and AD9834 and they work OK. However, I can still see some noise - mostly oscillator clock 50-80mV super imposed on the generated (sine/triangle) signal.
The passive LPF doesn't do anything to the signal.
The digital output is clear as it bypasses the DAC's output.

Could you take a scope snapshots before and after LPF  (let say 10kHz sine) and set vertical resolution at 50mV and horizontal at 5-20ns (smallest possible).
Make sure you turn off channel bandwidth limit function on the scope (if its there) otherwise you won't see the potential noise.

Peter

[Thaelin]

   Dont know the board obviously but tend to think if you could see the bare board you may well see a solid copper block under the said pins. Would save traces on the circuit area. Since you are dealing with frequency, the less to transmit signals across the better to me anyhow. I am in the process of making a three channel gen and I am trying to place things to keep the leads as short as possible.

thaelin

[Gregi]

Hi,

I have a question to those who have or know/tested the kit.

I have tested mine and it seems to work good, only one thing since I never had a function gen. before.
When I set it to a frequency, lets say 43kHz, what I see on the scope is that the square output keeps shifting back and forth, sometimes just a little sometimes a half unit of the time base. Frequency is stable, but the whole output shifts as the scope refreshes the screen.

So is this something normal or is there a problem somewhere?

Thanks,
Greg

[MeggerMan]

Hi Gregi,
Are you saying the freq. is changing?
My scope tells me the freq. of the pulse.
Check you are not using the sweep mode (run-----------) between f1 and f2.
Check the trigger level on your scope, if its not set right you will see drift.
On my scope if you use input B it is free running and cannot be set by the trigger.
If none of these work I will check 43KHz on my scope.
Regards
Rob