AD9850 DDS as a RF generator about wwvb HOT 13 CLOSED

Yeah im Australian, no wwvb here either!

Thanks for pointing me to that library, its actually a similar approach to what my new wwvb_jjy library is taking - but i use a union to access the bits as a buffer, jjy or wwvb. Interesting that it syncs on your watch, i will have to test it out against my clock (BALDR brand, same as @mr-sneezy) which arrived yesterday.

Also, i ordered that exact dds board a week ago so should be able to use the same test setup (when it eventually arrives). My library has worked with desk clocks, but not watches - i had been wondering if this is because the arduino outputs a 0 to 5v square wave instead of a -5 to 5v sine, looks like it may.

Ill have a look at that library and get back to you. In the meantime, if you wanted to test against an early release have a look at the tx example in my wwvb_jjy library. It requires my pwm library. Initialise the dds in setup, turn it off in the overflow isr and turn it on in the compare isr.

Cheers

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Okay im dumb. Those updates failed, i should be able to fix it easily enough though. I tested last night and got my new library syncing my desk clock but haven't updated the changes yet - needs a tidy up of debug code.

Ive reopened this until the new library is tested and working, then ill transition to that.

Cheers

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Hello.
As I'm not a good programmer, I'm testing the range of the signal from the ad9850.
I connected an AM loop antenna on the analog1 output pin of the DDS.
Even without a proper modulation, I could make a simple program that switches the 60khs carrier on and off in a regular half second interval.
Of course, the watch doesn't sync, but, it listens to the signal and shows "strong" signal even 3 meters away from the antenna.
An electronic technician told me that it's easy to extend the range even more by using a MOSFET transistor to amplify the signal.
My idea is that one transmitter could have the range all over the house.
cheers

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Oh, forgot to say...
Differently from de PWM output at arduino board, you should connect the other end of the antenna to the gnd pin in order to have a good transmission.

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Regarding the transmitter, you will need to check the applicable regulations on your country regarding transmit power. The example i use is current limited by grounding the antenna through a led - this is more to protect the arduino pin, although they are internally limited to 20mA anyways.

Generally you will be limited to 100mW ERP, which is Pt(av) × Gt. The max theoretical duty cycle is 73% over a 60s frame (7 markers at 20%, 53 low at 80%). Pt(av) = 5V × 20mA ×73% = 0.073W = 73mW. To keep under 100mW the max antenna gain would be 10×log10(100/73) = 1.36dB.

If you are not limited to 100mW you have a few options. You could use the arduino to switch in a higher voltage using a fet or op amp, or pull a higher current through a fet. The 2n2222 (800mA max) is a good common BJT which should work well, or a 2n7000 (200mA) if you wanted a mosfet (or BS170 - 500mA, a less common 2n7000 equivalent).

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remember the regs are always about ERP - effective radiated power.... at 60kHz - you will be more worried about planning regulations than transmitted power as the 1/4 length is huge....

Though careful matching is always a good idea to protect your transmitter driver..

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You mean I can't install a 1.25km antenna out the back 😄

Actually I did forget how terrible the gain of these antennas are. They are classified as being electrically small, and i make no effort at impedance matching so probably 'worse than -10dB' if my memory serves me correctly.

So @RoLorenzoni - ignore my warning. Also, @mr-sneezy tells me its 10mW, not 100mW.

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Ill keep this open for a little bit - but the wwvb_jjy library is now working for a simple example so ill resolved this issue in that repo 🤞

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Oh thanks.
I'll test the wwvb_jjy today.
I found this app on the web.
http://www.jrcomputing.com.au/Set_Watch/Set_Watch_Manual.html
May be useful, specially for you, because it's JJY too.

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Thanks for that, ill have to check it out.
Im closing this as i have an (untested) example in the new wwvb_jjy library - https://github.com/micooke/wwvb_jjy/blob/master/examples/AD9850_WWVB_tx/AD9850_WWVB_tx.ino

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Hey @baradhili did you end up getting a board from Wingsy?

https://forum.allaboutcircuits.com/threads/i-built-it-now-can-i-sell-it.130898/page-2#post-1089916

I wound be interested in the schematic and what antenna you are using.

Cheers

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