Burst period on function generator

[rwooduk]

Hi,

I am having to refresh my oscilloscope knowledge and am confused about one last function generator setting... Burst period.

If I have 1 cycle at say 700 kHz it is 1.43us. If I set number of cycles to 10 then that is 10 * 1.43us = 14.3us time. This is my ON burst.

So what is the burst period setting? How can I set say a 10ms burst if my ON 'burst' is already 28.6us as defined by my number of cycles and the frequency?

It is defined in the manual as "the time from the start of one burst to the start of next burst". But then in my example, if I set a burst period of 20ms, that means it would be ON for 14.3us and OFF for (20ms - 14.3us), which is a huge OFF time before the next burst. Is that correct?

I'm sure this is simple but I'm getting confused with the setting.

Thanks for any advice.

 

[Klystron]

Your analysis seems correct, for a signal generator module. My neurostimulator TENS unit has similar controls. E.g., after 20ms interval it fires a burst of duration 10us, then repeats the cycle.

In different terms the pulse width covers 10us at a pulse repetition time interval of 20ms.

The pulse width is a measure of the elapsed time between the leading and trailing edges of a single pulse of energy. The measure is typically used with electrical signals and is widely used in the fields of radar and power supplies. There are two closely related measures. The pulse repetition interval measures the time between the leading edges of two pulses but is normally expressed as the pulse repetition frequency (PRF), the number of pulses in a given time, typically a second. The duty cycle expresses the pulse width as a fraction or percentage of one complete cycle.

 

[rwooduk]

Your analysis seems correct, for a signal generator module. My neurostimulator TENS unit has similar controls. E.g., after 20ms interval it fires a burst of duration 10us, then repeats the cycle.

In different terms the pulse width covers 10us at a pulse repetition time of 20ms.

Thank you very much Klystron, I really wasn't so sure.

 

[Baluncore]

But then in my example, if I set a burst period of 20ms, that means it would be ON for 14.3us and OFF for (20ms - 14.3us), which is a huge OFF time before the next burst. Is that correct?

That is correct. RADAR produces a short pulse having only a few cycles at the carrier frequency, the receiver then listens for sufficient time for the reflection to return from maximum range.
Your "burst period" is the reciprocal of the Pulse Repetition Frequency = PRF.
Your "on burst" is the carrier pulse duration.

 

[rwooduk]

That is correct. RADAR produces a short pulse having only a few cycles at the carrier frequency, the receiver then listens for sufficient time for the reflection to return from maximum range.
Your "burst period" is the reciprocal of the Pulse Repetition Frequency = PRF.
Your "on burst" is the carrier pulse duration.

Many thanks!

 

[rwooduk]

Just one, last thing please. I am reading a paper that uses 100 Hz PRF so 10 ms Burst. This with 30% duty cycle (30% on, 70% off). 30% of 10ms is 3 ms. It's at 1.1 MHz so ~909.1 ns per cycle. So in the paper they must have used 3ms/909.1ns ~ 3300 cycles. Does this look like a correct calculation? Thanks again.

 

[Baluncore]

F_envelope = 100 pps; T_pulse = 10 ms;
Therefore; 3 ms on, 7 ms off;
3.0 ms * 1.1 MHz = 3300 cycles.
Correct.

 

[rwooduk]

Appreciated!