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Author Topic: DDS VFO using AD9850 2 output 180 degrees out of phase  (Read 312 times)
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KD6CXW
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« on: January 28, 2025, 10:21:05 AM »

the plan is to build a DDS VFO using a AD9850 to get 2 outputs 180 degrees out of phase and run each to a amplifier to boost signal then run to IXDD414 drivers to run a 24 MOSFET E-class amplifier .
am I thinking correctly or am I missing something ?
thanks
John
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vk3alk
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« Reply #1 on: January 31, 2025, 10:35:04 PM »

Hi John...

Your thinking is fine....
Have built up many circuits similar to what you need as well...
Steve on his Web Site has this circuit...

http://www.classeradio.com/vfo_2_band.pdf

Just after the VFO is Q2 .... you could inject your DDS signal there and fiddle with the 50K pot....
The output doesn't have to be pretty but does need to be over 2 volts to change the state of the 74112...
On Jays Web Site W1VD he has a VFO there too using 7474 Flip Flops....
I use those ICs more often then the 74112....

You may have to add a little amplifer after the DDS just to bring the amplitude up a bit ....
Play around to get that part of the circuit reliable and the rest is quite easy...


Wayne

PS:  as far as your 24 Fet TX goes I haven't built one using so many FETs so probably cannot help you there.

Steve would be the best bet and K1KBW has a WEB site that could be of some use as well....


Wayne




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vk3alk
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« Reply #2 on: February 03, 2025, 09:03:17 PM »

I found this circuit works very well and is easily adapted to your needs...

https://www.qsl.net/wn5y/svfo.htm

The write up is right down the bottom of the page and is an interesting read ...
I used it on the 20M AM TX and maybe an overkill but is very reliable which is something your 24 FET TX needs...
The NE602 and a DDS unit are a good match....
The output goes into 7474 Flip Flops and you have your dual 180 degrees outputs etc:

I have to makeup this circuit for an upcoming project so could fast track it and post the results....
Also was interested in Phil AC0OB timing circuit as well so will use and see how it goes...


Wayne




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KD6CXW
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« Reply #3 on: Yesterday at 08:03:21 PM »

Thanks Wayne , I went to the sites and found others as well .
Waiting for parts and time to work on the VFO , I'll  post as the project progresses.

73's
John
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