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Pulse modulation, with a different place for the pulse each 20ms.

Question asked by antoine on Jun 21, 2013
Latest reply on Jul 1, 2013 by tabbott

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Hi Guy,

I am trying to generate a signal on which a pulse modulation is applied.
The features of the modulation are a width of 0.1ms for each pulse and a pulse period of 1.1ms. Furthermore, in this signal, one bit lasts 20ms.

Now I would like to move back the pulses every 20ms. For example, for the first bit the pulses begins at t = 0 ms,
then I move back it of 0.1ms, thus for the second bit I would like that the pulses begin at t = 20.1 ms rather than 20ms...

I looked at the "SCPI command manual" ( I command the generator Agilent MXG N5182A thanks to the SCPI commands) and I found a command to delay the pulses:

[:SOURce]:PULM:INTernal:DELay[1]|[2] |UP|DOWN

However, how can I tell the generator to do that every 20ms ? Can I use the following command:

[:SOURce]:PULM:INTernal:DELay:STEP

I am not sure I understood exactly what is the purpose of the second command...

Thanks for your help and have a nice week end!!

Antoine

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tabbott

Jun 25, 2013 8:55 AM

Hi Antoine -

The command –
:SOURce:PULM:INTernal:DELay[1]|[2] |UP|DOWN
Sets the delay relative to the pulse sync signal.
If is used then the delay is set according to these parameters.
For example :SOURce:PULM:INTernal:DELay1 0.01ms sets the delay for 10usec.

The |UP|DOWN parameters are used in conjunction with the second command –
:SOURce:PULM:INTernal:DELay:STEP
For example :SOURce:PULM:INTernal:DELay:STEP 0.01ms
Set the delay step to be 10usec. Now using
:SOURce:PULM:INTernal:DELay1 UP
Increment the delay by 10usec each time.

It is not quite clear to me what you are trying to do.
Are you calling 18 periods of you signal one bit?
What do you mean by moving the pulses back every 20mS?
Are the pulses running continuous or are they externally triggered?
Are you staggering one pulse across the 1.1mS?

Regards -

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antoine Jun 27, 2013 7:45 AM

First of all thanks for your answer,

actually I have some bits, and each bit is composed of 20 codes C/A (all the sames) composed of 1000 chips. Thus, one bit is made up of 20x1000 chips. One bit lasts 20ms and each code C/A code lasts 1ms.

So what I want to do, it is to pulse 1/10 th of each C/A code. That's why I set a pulse width of 0.1ms and I want to cover the whole C/A code during 10ms thus I set a pulse period of 1.1ms so that for each C/A code the pulse is moved forward of 0.1ms.
Then for the first C/A I cover the 100 first chips, on the second C/A I cover the chips from 101 to 200 etc etc... After 10 ms I covered the 1000 chips.

I think I succeed to do that but now I want to change the sequence. I mean for the 11th ms I don't want the pulse to begin at the 1st chip but at the 50th for example. So It would mean to delay it of -10.5 ms. Do you think this is possible?

I hope I am clear enough... Thanks for your help!

Antoine

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tabbott

@ antoine on Jul 1, 2013 4:19 PM

Hi Antoine -

Thanks for clearing this up. I now have a better understanding of what you are attempting.

If the signal that carries the C/A code is continuous then it seems that setting the pulse width to .1mS and the period to 1.1mS would cover the 100 first chips on the first pulse then the next 100 on the second, covering 1000 chips after 10ms as you have seen.

Now for the 50th chip…

One way to accomplish this is to use the pulse train option of the N5182A-320:
http://www.home.agilent.com/en/pd-1871912-pn-N5182A-320/pulse-train-generator?cc=US&lc=eng

You could define a pulse train:
Item     On Time     Off Time      Repeat
1     .1ms     1ms     9
10     .1ms     10.5ms     1
11     .1ms     1ms     1

Note: this produces the 10 pulses allowing you to pulse the 1000 chips in 100chip intervals then there is a 10.5ms delay and the 11th pulse begins at the 50th chip.

The last thing needed would be to synchronize the pulses with you C/A signal.

Regards -

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3 Replies

tabbott Jun 25, 2013 8:55 AM
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Correct Answer
Hi Antoine -

The command –
:SOURce:PULM:INTernal:DELay[1]|[2] |UP|DOWN
Sets the delay relative to the pulse sync signal.
If is used then the delay is set according to these parameters.
For example :SOURce:PULM:INTernal:DELay1 0.01ms sets the delay for 10usec.

The |UP|DOWN parameters are used in conjunction with the second command –
:SOURce:PULM:INTernal:DELay:STEP
For example :SOURce:PULM:INTernal:DELay:STEP 0.01ms
Set the delay step to be 10usec. Now using
:SOURce:PULM:INTernal:DELay1 UP
Increment the delay by 10usec each time.

It is not quite clear to me what you are trying to do.
Are you calling 18 periods of you signal one bit?
What do you mean by moving the pulses back every 20mS?
Are the pulses running continuous or are they externally triggered?
Are you staggering one pulse across the 1.1mS?

Regards -
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antoine Jun 27, 2013 7:45 AM
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Correct Answer
First of all thanks for your answer,

actually I have some bits, and each bit is composed of 20 codes C/A (all the sames) composed of 1000 chips. Thus, one bit is made up of 20x1000 chips. One bit lasts 20ms and each code C/A code lasts 1ms.

So what I want to do, it is to pulse 1/10 th of each C/A code. That's why I set a pulse width of 0.1ms and I want to cover the whole C/A code during 10ms thus I set a pulse period of 1.1ms so that for each C/A code the pulse is moved forward of 0.1ms.
Then for the first C/A I cover the 100 first chips, on the second C/A I cover the chips from 101 to 200 etc etc... After 10 ms I covered the 1000 chips.

I think I succeed to do that but now I want to change the sequence. I mean for the 11th ms I don't want the pulse to begin at the 1st chip but at the 50th for example. So It would mean to delay it of -10.5 ms. Do you think this is possible?

I hope I am clear enough... Thanks for your help!

Antoine
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- tabbott @ antoine on Jul 1, 2013 4:19 PM
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  Correct Answer
  Hi Antoine -
  
  Thanks for clearing this up. I now have a better understanding of what you are attempting.
  
  If the signal that carries the C/A code is continuous then it seems that setting the pulse width to .1mS and the period to 1.1mS would cover the 100 first chips on the first pulse then the next 100 on the second, covering 1000 chips after 10ms as you have seen.
  
  Now for the 50th chip…
  
  One way to accomplish this is to use the pulse train option of the N5182A-320:
  http://www.home.agilent.com/en/pd-1871912-pn-N5182A-320/pulse-train-generator?cc=US&lc=eng
  
  You could define a pulse train:
  Item     On Time     Off Time      Repeat
  1     .1ms     1ms     9
  10     .1ms     10.5ms     1
  11     .1ms     1ms     1
  
  Note: this produces the 10 pulses allowing you to pulse the 1000 chips in 100chip intervals then there is a 10.5ms delay and the 11th pulse begins at the 50th chip.
  
  The last thing needed would be to synchronize the pulses with you C/A signal.
  
  Regards -
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Pulse modulation, with a different place for the pulse each 20ms.

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