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Generating The 27Mhz sine Wave form

sleepless

New Member
Does any one have idea how to generate the waveform as shown in the attached image i need a signal of 27Mhz which on for 100 microseconds and off for 900 microsecnods.Thanks
 

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ronsimpson

Well-Known Member
Most Helpful Member
Amplitude? (Volts)
Must the 27mhz start and stop clean? like in your picture. Can the 27mhz start randomly? Each time in at a different phase of the 27mhz.

If you need one easy. $100.00 usd Dual Channel DDS Function Arbitrary Waveform Signal Generator you can literally draw out a wave form and the ARB will produce it. I have not use a ARB from BangGood.com but the one that I have used, you can draw a waveform with up to 8000 points. Have channel A effect Channel B. Do things like make random nooise.
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sleepless

New Member
Gate a 27MHz xtal oscillator on and off as required.

However, what are you trying to do?.
Hi yes i tried from 27MHZ crystal i get the sine wave but dont have any idea how to on and off .I need the 27MHz sine wave on for 100micro seconds and off for 900 micro seconds i am doing a project on Pulsed electromagnetic field in university
 

ronsimpson

Well-Known Member
Most Helpful Member
There are two parts to what you need beyond the 27mhz.
1) you need a digital signal 100uS/900uS. That can come from a nec555.
2) Analog Switch. There are many types. This one needs 5 volt supply. Run the 27mhz through the A to B pins. The signal needs to stay in the range of 0 to 5 volts. The 100uS/900uS signal goes to C.
The switch can pass up to 300mhz. When closed it has 5 ohms and when open it leaks about 0.1uA.
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sleepless

New Member
Oh thanks a lot what about if i use an aurduino to generate 100/900 signal ..?How to connect the 27mhz signal to the switch it.I mean where to connect positive of the signal and where the ground of the signal????What if i use the BJT as switch.Please guide.
 

ronsimpson

Well-Known Member
Most Helpful Member
There are many things I do not know. If the 27mhz can drive a load of 50 ohms.
But here is how I would do it. The supply comes from the Aurduino.
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ronsimpson

Well-Known Member
Most Helpful Member
just enable or disable the supply voltage to the 27MHz oscillator.
27MHZ crystal
We know nothing about the "crystal oscillator". It might start up unstable. (frequency and amplitude) Interrupting the supply sounds good and simple. I have seen xtal oscillators start up at a harmonic for a while. Some oscillators are not at 50% duty cycle at startup.

It is a little strange that he is getting "sign wave" from the oscillator. So it probably not a square can digital "ttl" oscillator. Or maybe the scope is not good and it is a square wave. Or maybe a xtal + transistor oscillator. Maybe a signal generator. Or ???
We can not go farther with out much more information.
 

JimB

Super Moderator
Most Helpful Member
Or, as micro-controllers are now being considered, why not use the micro to switch a DDS module which uses something like an AD9850 synthesiser chip.

That way our OP gets:
good frequency control from the DDS
sinewaves from the DDS
good burst timing from the micro controller

Note DDS = Direct Digital Synthesiser

JimB
 

JimB

Super Moderator
Most Helpful Member

ronsimpson

Well-Known Member
Most Helpful Member
set the frequency to zero.
Will the output of the 27mhz just freeze where it is? I think the 27mhz will freeze randomly. Maybe at 5V or 0V or 2.395V. The off state voltage will be different every time. (really don't know .... just asking)
---edited---
It looks like by changing the current in RSET you can AM modulate the signal. So through RSET pin you should be able to shut down the output.
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JimB

Super Moderator
Most Helpful Member
I did a quick test, I wrote some code for a PIC which did the following:

set the frequency to 27MHz
wait 1mS
set the frequency to 0MHz
wait 10mS
repeat

Loaded that into my AD9851 based signal source, and it worked quite well.
The phase at which the frequencies started and stopped was rather random, but it did generate 1mS bursts as required.

JimB
 

sleepless

New Member
I did a quick test, I wrote some code for a PIC which did the following:

set the frequency to 27MHz
wait 1mS
set the frequency to 0MHz
wait 10mS
repeat

Loaded that into my AD9851 based signal source, and it worked quite well.
The phase at which the frequencies started and stopped was rather random, but it did generate 1mS bursts as required.

JimB
Thanks could you please share your schematic and code etc?
 

JimB

Super Moderator
Most Helpful Member
Thanks could you please share your schematic and code etc?
Difficult.

The piece of equipment which I "modified" for the test is something which just grew over the years, and as a result there is no schematic, it is all in my head.
That is not usually how I work, but in this case, it is what it is.

As for the code, which is well kept and documented, I just inserted a few new lines of code into a much larger existing piece of code which in turn calls several different subroutines.
So although the little patch which I created for the test is probably less than ten lines, it calls a lot of other code.

JimB
 

ronsimpson

Well-Known Member
Most Helpful Member
As long as we are looking at DDS boards:
This board has 4 channels. It also has programmable output voltage. So for the off time it can be set to 0V out. Or possibility channel 1 can effect channel 2, examples in the data sheet. See AS9959.
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RF Signal Source AD9959 Signal Generator Four Channel DDS Module
 

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