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NI5401 external trigger frequency hop

Dear,

I am having problems with my NI 5401 function generator card.

I have a trigger signal connected between the trigger and the DGND pins on the pattern out connector in order to switch between different frequency in frequency hopping mode. The response of the card is some how correlated to the applied external trigger signal but the during the switching pulse the card seems to switch between the two frequencies a couple of times creating an irregular waveform.

Do you have any idea what is wron? Could it be the way I connected the trigger or is there an internal problem?

Thanks a lot in advance

Marc Hauptmann

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Hello Mr. Hauptmann,

 

What do you use to create the trigger signal?

How should the trigger signal look like?

Do you have the possibility to look at (measure) the trigger signal?

Kind Regards,
Thierry C - CLA, CTA - Staff R&D Engineer, RF Semiconductor Test - National Instruments
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Dear Mr.Coppens,

thank you for the reply. The trigger signal (standard ttl-pulse) will externally be generated via a timing circuit which is itself being triggered by a standard pulse generator. The timing circuit creates two pulses (~1us) at the rising and falling edge respectively of the incoming pulse. I noticed that the behavior of the NI5401 changes with the pulse width of the trigger pulse, meaning that a pulse width of around 250 ns seemingly switches the card in a stable fashion. Could this be the problem?

Thanks a lot for your help

With kind regards

Marc Hauptmann

P.S. Trigger Signal looked okay in either case

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Hello Mr. Hauptman,

 

I haven't heard of an effect like this before and I also didn't find any earlier occurence of a problem/issue like this one in our database.

 

So there's no "bouncing" of the TTL-signal at the output of your timing circuit?

Does the 1us indicate the pulse width of both generated TTL-pulses?

How long does this "switching" effect take place?

Does it eventually end up in the right state?

Kind Regards,
Thierry C - CLA, CTA - Staff R&D Engineer, RF Semiconductor Test - National Instruments
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Dear Mr. Coppens,

thanks a lot for your answer.

There is no bouncing of the trigger signal (measured before the input of the NI card). Both pulses are each 1 us long (with a time delay of 1ms between two pulses). During this 1 us of pulse duration the card switches randomly between the different frequencies as if being triggered multiple times (1 frequency doesn't last longer than a couple of oscillation cycles). So in the end up the frequency after 1 completed pulse is random as well. It seems that, when using pulses of 250 ns, the switching occurs properly, though sometimes the card seems "to miss" a  trigger event and the order of the frequencies with respect to the original pulse (from the standard pulse generator) is inverted.

Do you have an idea, where the effect is coming from? Is it safe to work with pulses < 500 ns?

Thank you very much and kind regards

Marc Hauptmann

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Hello Mr. Hauptman,

 

As specified in this document the minimum pulse width is 20 ns and there is no maximum pulse width specified.

 

Keep in mind that you can only trigger on the rising edge.

 

Can you send me the code you're currently using?

Kind Regards,
Thierry C - CLA, CTA - Staff R&D Engineer, RF Semiconductor Test - National Instruments
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Dear Mr. Coppens,

I am currently using the standard function generator application with frequency hopping function. (I later want to implement this into labview code)

As I stated earlier, I am using a pulse doubling circuit in order to create two pulse at the rising and falling edge of the triggering input pulse. The rising edges of these 2 pulses will therefore trigger the function generator. As I also stated earlier, it seems too me, that the triggering is working correctly once the pulse length of the double pulses is below 500 ns. If length surpasses that value, the FG card starts to act strangely, shifting frequencies randomly for the duration of the respective pulse.

Thank you very much for your help

Best regards

Marc Hauptmann

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Hi,

sorry for the absence - I've been busy and then on vacation. However - I could solve the problem by stabilizing the circuit that creates the double-pulse to trigger the FG-card and fixing the trigger pulse-length to 500 ns.

Thanks for the helpful remarks and support

Yours sincerely

Marc

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