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Author Topic: The I Q VFO Pro DDS vfo  (Read 850 times)
9H1FQ
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Posts: 144




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« on: January 17, 2010, 12:17:12 AM »

Hi all.
I have just finished building  a DDS vfo called IQ vfo pro.

I am having a funny startup problem.

The unit is made up of two boards, one containing the PIC control and the other the RF section.

Connecting the 5 volts supply to the control board, but disconnecting the 3 volts supply to the RF board, the control board works fine.

When connecting the 3 volts supply ( which is coming from the 5 volts supply) to the RF board, all voltages drops down. And both boards cease to operate .

However, connecting and re connecting the 3 volts supply, and re-setting the pic, the whole thing works fine. I have to do this procedure every time I power up

Could it be a tantalum capacitor?
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K2DC
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« Reply #1 on: January 17, 2010, 01:01:23 AM »

Paul,

  Perhaps you could get in touch with the designer, Craig AA0ZZ.  His email is aa0zz at arrl dot net.  I'm not familiar with the kit, but I do know that in mixed signal applications isolation between digital and analog power and isolation between digital and analog ground can be critical.  Maybe Craig can help you.

GL & 73,

Don, K2DC
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NJ2E
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« Reply #2 on: January 17, 2010, 05:49:24 AM »

Have you joined the Yahoo Group "DDS-VFO"? I wouldn't be surprised someone else has faced the same problem. It looks like this is the primary support source for this project. Good Luck, Don NJ2E
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K8AC
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« Reply #3 on: January 17, 2010, 06:55:53 AM »

The best place for help is the DDS-VFO Yahoo group.  There you'll find dozens of guys who have successfully built the IQPro.  Since I've built a couple myself, I'll ask you a few things that you'll be asked on the forum.

1. Did you use Craig's 5V switching power supply or something else? 

2. I don't have an IQPro opened up to look at right now, but it appears that HDR13 on the RF board can be unplugged to disconnect the 3V regulator and supply from the reference clock module and the DDS module.  What happens when you unplug HDR13?  If you still have the problem take a hard look at the components in the 3V regulator (and of course your 5V supply).

3. Did you follow the steps in the Assembly Notes that have you test the power supply voltages before completing the assembly?

4. Did you solder the DDS chip to the board yourself or did it come already mounted?  In either case, check VERY carefully for solder bridged pins. 

5. As you know, the VFO really doesn't start out as two boards - it comes as a single board which you can choose to split into two boards in case you don't have room for the single board.  When you split the two boards, did you connect all the jumpers between the two (9 in all).

6. Did you build the transistor RF amp stages?  If so, do you have the same output level from both I and Q outputs when it's working? 

I'd guess that there's a problem in the 5V supply, the 3V regulator, or with solder bridge(s) on the RF board.  When you say that the control board works fine, do you mean that all the pushbuttons do what they're supposed to do and that the display always shows what it's supposed to? 
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