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PHSNA for DDS-60 and NANO checkout

km5ht@...
 

I have built the PHSNA for DDS-60 and NANO version of the PHSNA.  I am just starting checkout.  I set the output of the DDS60 module for 2V P-P at J8 BNC on the scope with no load at 10 Mhz.  


If I scope J8 BNC and tie this to the power meter with a short jumper cable, the output at J8 drops to about 1V P-P.  Is this signal loading normal, or do I have something wrong with my power meter?


The DDS60 was built from a kit.  All other surface mount parts came from Mouser.  The through hole parts came from my junk box, but all resistors and caps were tested with meters before installing them including the surface mount stuff.


73 Steve, KM5HT

Nick Kennedy
 

That sounds normal to me. Your first test was the open circuit output. In the second test, you have a voltage divider between the 50 source resistance of the DDS-60 and the 50 ohm input resistance of the log power meter.

73-

Nick, WA5BDU

On Mon, Dec 28, 2015 at 9:55 AM, km5ht@... [PHSNA] <PHSNA@...> wrote:
 

I have built the PHSNA for DDS-60 and NANO version of the PHSNA.  I am just starting checkout.  I set the output of the DDS60 module for 2V P-P at J8 BNC on the scope with no load at 10 Mhz.  


If I scope J8 BNC and tie this to the power meter with a short jumper cable, the output at J8 drops to about 1V P-P.  Is this signal loading normal, or do I have something wrong with my power meter?


The DDS60 was built from a kit.  All other surface mount parts came from Mouser.  The through hole parts came from my junk box, but all resistors and caps were tested with meters before installing them including the surface mount stuff.


73 Steve, KM5HT


km5ht@...
 

Nick;
    Thanks for the quick reply.  Just wondering how I should proceed then, set the power meter for 4 dBm, and/or crank up the output of the DDS60 for 10 dBm?

73 Steve, KM5HT


---In PHSNA@..., <kennnick@...> wrote :

That sounds normal to me. Your first test was the open circuit output. In the second test, you have a voltage divider between the 50 source resistance of the DDS-60 and the 50 ohm input resistance of the log power meter.

73-

Nick, WA5BDU

On Mon, Dec 28, 2015 at 9:55 AM, km5ht@... [PHSNA] <PHSNA@...> wrote:
 

I have built the PHSNA for DDS-60 and NANO version of the PHSNA.  I am just starting checkout.  I set the output of the DDS60 module for 2V P-P at J8 BNC on the scope with no load at 10 Mhz.  


If I scope J8 BNC and tie this to the power meter with a short jumper cable, the output at J8 drops to about 1V P-P.  Is this signal loading normal, or do I have something wrong with my power meter?


The DDS60 was built from a kit.  All other surface mount parts came from Mouser.  The through hole parts came from my junk box, but all resistors and caps were tested with meters before installing them including the surface mount stuff.


73 Steve, KM5HT


Nick Kennedy
 

Well, it's kind of "dealers choice" where to set your power output. But once you've set it you calibrate the system based on that.

Many people go with -10 dBm output from the DDS so they can drive crystals without fear of over-driving them.  Others want more maximum output and will just use attenuators as needed or desired when testing crystals.

Remember that when you measure 2 Vpp open circuit, that's not actually a power level since the DDS is not putting out power. True, 2 Vpp into 50 ohms would be +10 dBm and 1 Vpp is 6 dB less than that.

I looked at Jim's schematic for a PHSNA with a DDS-60 and he has an additional 10 dB attenuator after the DDS-60 board. That will allow you to get down to -10 dBm if desired or have a bit more output if you wish, using your adjustment pot. The attenuator also makes the DDS look more like a constant 50 ohm source, so it has that value in addition to reducing output.

73-

Nick, WA5BDU


On Mon, Dec 28, 2015 at 11:28 AM, km5ht@... [PHSNA] <PHSNA@...> wrote:
 

Nick;

    Thanks for the quick reply.  Just wondering how I should proceed then, set the power meter for 4 dBm, and/or crank up the output of the DDS60 for 10 dBm?

73 Steve, KM5HT


---In PHSNA@..., wrote :

That sounds normal to me. Your first test was the open circuit output. In the second test, you have a voltage divider between the 50 source resistance of the DDS-60 and the 50 ohm input resistance of the log power meter.

73-

Nick, WA5BDU

On Mon, Dec 28, 2015 at 9:55 AM, km5ht@... [PHSNA] <PHSNA@...> wrote:
 

I have built the PHSNA for DDS-60 and NANO version of the PHSNA.  I am just starting checkout.  I set the output of the DDS60 module for 2V P-P at J8 BNC on the scope with no load at 10 Mhz.  


If I scope J8 BNC and tie this to the power meter with a short jumper cable, the output at J8 drops to about 1V P-P.  Is this signal loading normal, or do I have something wrong with my power meter?


The DDS60 was built from a kit.  All other surface mount parts came from Mouser.  The through hole parts came from my junk box, but all resistors and caps were tested with meters before installing them including the surface mount stuff.


73 Steve, KM5HT