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Author Topic: Homebrew 3 Channel Pure SIN Generator ( 0 ... 60MHz )  (Read 41094 times)

Yucca

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Homebrew 3 Channel Pure SIN Generator ( 0 ... 60MHz )
« on: September 23, 2009, 07:32:14 PM »
I'm starting this thread to document my build of a 3 channel pure SIN generator with the following

specs:
==============================
3 Channels (hopefully phase locked).

0 ... 60MHz with 1Hz resolution.

4V p2p into 50 Ohm.

Microcontroller controlled.

3D sweeping capability (sweep width and resolution adjustable on each channel)

When sweeping samples analog input signal in order to hunt for optimum power out. 8bit sampling taken through digital adjustable attenuator (16bit) so that clipping is avoided and true maxima is found. This effectively increases sampling resolution to 24bits.

Ability to log scan results into PC over USB cable for analysis on PC in excel etc.
==============================

I already have a 2nd hand tektronix FG504 sig genny which is great and handy but the output, like most bench gennys, is like a wailing drunk karaoke singer when compared to a true radio quality signal required for experiments in intermodulation.

The hard work I will buy premade in the form of 3 x DDS60 modules, designed and used by amateur radio enthusiasts. The design has evolved over quite a few years and is very stable:

http://www.amqrp.org/kits/dds60/index.html

The modules will be under the control of an ATMega Microcontroller (under the screen in the photo).

I am thinking about and working on the user interface at the moment. The user can either use the small joystick switch you can see in the photo just to the right of the screen, or they can attach a rotary shaft encoder and spin a wheel to intuitively sweep through frequencies having first selected the channel and decade to adjust.

I'll post more as the build and programming progresses.

I posted in TPU section because 3 chan sin is often spoken of in theories of operation. But I would prefer to post in an "Equipment & Measurement" section. That section could include reviews of existing equipment, which would attract lots of search hits, measurement techniques and other tips on how to build and use stuff or how to improvise etc.

Yucca.
« Last Edit: September 23, 2009, 07:54:34 PM by Yucca »

dankie

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Re: Homebrew 3 Channel Pure SIN Generator.
« Reply #1 on: September 23, 2009, 07:55:16 PM »
Does the TPU require AC or a sine waveform .

At higher frequencies the square wave will be rounded off a bit , a vacuum tube looks like it rounds off the edges also .

I think you are overcomplicating the task at hand , controlling the "phase" of each signal will be hard with a sine wave generator . It can be done more easily with logic lvl pulsing . Then amplified to be smooter .

Yucca

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Re: Homebrew 3 Channel Pure SIN Generator ( 0 ... 60MHz )
« Reply #2 on: September 23, 2009, 07:56:01 PM »
Well, I'm commited now; Just purchased the 3 x DDS60 modules. Will now have to explain to my better half exactly what the hell they are lol!

Yucca

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Re: Homebrew 3 Channel Pure SIN Generator.
« Reply #3 on: September 23, 2009, 08:16:35 PM »
Does the TPU require AC or a sine waveform .

I dunno, better ask SM. As you know pure variable sin is not easy to do, variable square is easy.

What do you mean AC or SIN? pure AC is pure SIN.

At higher frequencies the square wave will be rounded off a bit , a vacuum tube looks like it rounds off the edges also .

Rounded squares aren't pure freq, square waves are composed of odd integer harmonics of the fundamental. In experiments regarding intermodulation this is tantamount to cluttering noise.

It is easy to turn square into sin by using a lowpass filter set to roloff at fundamental but every time you change freq you have to alter component values. This genny will give very pure sin at any freq rock solid at 1Hz resolution. A nice bit of kit however you look at things.

I think you are overcomplicating the task at hand , controlling the "phase" of each signal will be hard with a sine wave generator . It can be done more easily with logic lvl pulsing . Then amplified to be smooter .

As I said I would prefer to post in an eqpuipment section. I want a 2 chan pure sin gen anyway for stuff other than TPU research, I just thought I'd add a 3rd chan to explore Bruces ideas. The equipment will not be solely for TPU research. I'm just thinking cover lots of combinations of various RF interference phenomena in various coil configs and see if I spot any anomolies worthy of further investigation. I'm just figuring it'll please me more than watching telly because I enjoy programming micros and building things.  To buy a piece of equipment with these specs would cost a few grand.

With regard to phase the chips are digital (they are a complex logic circuit with a final DAC stage) and all driven by xtal clocks, these clocks can be phase locked and so the derived frequencies can also be phase locked and adjusted with some effort in interlinking and programming.

Peterae

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Re: Homebrew 3 Channel Pure SIN Generator ( 0 ... 60MHz )
« Reply #4 on: September 23, 2009, 08:18:32 PM »
Go for it Yucca

A great bit of kit for the bench, and future TPU exploration work.

Not sure if the feedback idea will work , as SM has mentioned you can expect to find a hole in your bench if you find the correct frequency's, might be best a put it in a flame proof box  ;D

Yucca

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Re: Homebrew 3 Channel Pure SIN Generator ( 0 ... 60MHz )
« Reply #5 on: September 23, 2009, 11:01:18 PM »
Go for it Yucca

A great bit of kit for the bench, and future TPU exploration work.

Not sure if the feedback idea will work , as SM has mentioned you can expect to find a hole in your bench if you find the correct frequency's, might be best a put it in a flame proof box  ;D

Cheers Peter,

I'm putting opto isolator in feedback path. But you are right, perhaps if the "worst case" intermod combination is found in the correctly wound device then my unit may be zapped along with the rest of my bench!

p.s dont underestimate the Smith rig you are building, this afternoon I lost a 1gig memory card that was sat on the bench about 50cm away. It is now unreadable and unformattable. I was putting less than 5W into HV module.
« Last Edit: September 23, 2009, 11:32:01 PM by Yucca »

Peterae

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Re: Homebrew 3 Channel Pure SIN Generator ( 0 ... 60MHz )
« Reply #6 on: September 23, 2009, 11:16:29 PM »
Sorry to hear that Yucca.
I am setting up a bench in an underground disused room i have access to, to try and isolate any modern technology as anywhere else is packed full of the stuff and to try to stop radiation of the noise generated.

A good ground should be easy as well, just hope it doesnt stop the OU from showing up.

To think if Tesla powered up his giant Tesla these days he would probably knock every computer and cell phone out for miles LOL


BEP

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Re: Homebrew 3 Channel Pure SIN Generator ( 0 ... 60MHz )
« Reply #7 on: September 24, 2009, 04:43:15 AM »
@Yucca,

Over the past few years the 'hardware' oriented cells in my brain haven't had much stimulation.

THIS has them all buzzing again! Yes, I know. The parts aren't that hot but the combination, possibilities and the idea..... ;D

TPU or not I could find several uses for such a beast. This makes me yearn for the familiar smell of hot solder joints.

I write WindBlows/*Nix software (real coding - not 'modern' software development) for relaxation.

Please keep us informed how it goes. It sounds like you don't need help with software. If you do, send me a list of wants & needs. I'll be happy to look into it!

Yucca

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Re: Homebrew 3 Channel Pure SIN Generator ( 0 ... 60MHz )
« Reply #8 on: September 24, 2009, 05:00:25 AM »
@Yucca,

Over the past few years the 'hardware' oriented cells in my brain haven't had much stimulation.

THIS has them all buzzing again! Yes, I know. The parts aren't that hot but the combination, possibilities and the idea..... ;D

TPU or not I could find several uses for such a beast. This makes me yearn for the familiar smell of hot solder joints.

I write WindBlows/*Nix software (real coding - not 'modern' software development) for relaxation.

Please keep us informed how it goes. It sounds like you don't need help with software. If you do, send me a list of wants & needs. I'll be happy to look into it!

Thanks Bep, when it comes to writing a desktop computer interface (to log and maybe display scan data etc) then your expertise could be good.

Most of my time spent on this project will be software. The hardware is all pretty much plug and play modules. Of course I´ll have to fire up the soldering iron a little and also make some enclosure for it.

Stay tuned as I develop I´ll post more, probably post a short vid demoing the user interfaces main screen soon.

Yucca

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Re: Homebrew 3 Channel Pure SIN Generator ( 0 ... 60MHz )
« Reply #9 on: September 24, 2009, 05:04:42 AM »
Yucca, All I can say is   "NICE!"  .

(The mentioned specs are excellent!  Should do the job, no matter the job.)

Cheers Loner, the tight specs are mainly thanks to the IC manufacturer and the guys who designed and build the DDS modules, awesome technology made available to hobby level experimenters!

BEP

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Re: Homebrew 3 Channel Pure SIN Generator ( 0 ... 60MHz )
« Reply #10 on: September 24, 2009, 05:30:09 AM »
Thanks Bep, when it comes to writing a desktop computer interface (to log and maybe display scan data etc) then your expertise could be good.

Most of my time spent on this project will be software. The hardware is all pretty much plug and play modules. Of course I´ll have to fire up the soldering iron a little and also make some enclosure for it.

Stay tuned as I develop I´ll post more, probably post a short vid demoing the user interfaces main screen soon.

If required, I can hack or create PC drivers as well  :)

otto

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Re: Homebrew 3 Channel Pure SIN Generator ( 0 ... 60MHz )
« Reply #11 on: September 24, 2009, 06:24:06 AM »
Hello all,

@Yucca

very nice "monster" but ... it will NOT make the coils "happy".

Otto

Yucca

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Re: Homebrew 3 Channel Pure SIN Generator ( 0 ... 60MHz )
« Reply #12 on: September 24, 2009, 04:13:04 PM »
Hello all,

@Yucca

very nice "monster" but ... it will NOT make the coils "happy".

Otto

Hi Otto, why not? are you thinking square waves are needed? or maybe PWM?

If so then I could feed the outputs through digital circuitry and FETs in order to get square waves and maybe PWM from 10...90% by using comparator. My frequency in that scheme would be limited to 10...20MHz because of FET and driver speed. Of course I would still have up to 3D sweeping capability.

It will be nice for me to have a true calibrated signal source and I can make use of 1channel for lots of other things, I decided to do 3 channel because the modules are not that expensive considering the spec.

Yucca.

Yucca

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Re: Homebrew 3 Channel Pure SIN Generator ( 0 ... 60MHz )
« Reply #13 on: September 24, 2009, 04:21:06 PM »
If required, I can hack or create PC drivers as well  :)

Now that might be very handy! Thanks for the offer BEP! 8)

The micro board has a FT232RL USB to Serial UART chip on it:

http://www.ftdichip.com/Documents/DataSheets/DS_FT232R_V204.pdf

Peterae

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Re: Homebrew 3 Channel Pure SIN Generator ( 0 ... 60MHz )
« Reply #14 on: September 24, 2009, 09:53:38 PM »
Hi Yucca

I think you are going to have trouble syncing them together, this is from the data sheet and it specifys that a master clock should feed all 3 DDS chips.

Note: For those who may be operating multiple AD9851 evalu
a tion boards from one computer, a MANUAL FREQUENCY
UPDATE option exists. By eliminating the automatic issuance
of an FQ_UD, the user can load the 40-bit input registers of
multiple AD9851s without transferring that data to the internal
accumulators. When all input registers are loaded, a single
FREQUENCY UPDATE pulse can be issued to all AD9851s.
A block diagram of this technique is shown in the AD9851 data
sheet as a quadrature oscillator application. This single pulse
synchronizes all the units so that their particular phases and
frequencies take effect simultaneously.

Proper synchronization
requires that each AD9851 be clocked by the same reference
clock source and that each oscillator be in an identical state while
being programmed. RESET command ensures identical states.
When manual frequency update is selected, a new box labeled
FREQUENCY UPDATE will appear just above the frequency
sweeping menu. Clicking the box initiates a single FQ_UD pulse.


The good news is that you should be able to remove all three clock oscillators from each DDS board and connect a small board to all 3 clock pins on each DDS board as they have provided plated through the holes for pin osc chips as well as the used SM osc modules.
For true phase syncing you will need the track length the same to each DDS chip.
You will need to issue a frequency update to all DDS chips at the same time as said above.