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Sweep output debugging

Marcus Gustafsson
 

Hi all,


I'm starting a new thread since I'd like the previous one to be about the PHSNA SW.


Ok, I've done some debugging to see what's wrong with my PHSNA. I'll take the long version, hopefully it does not become too tedious. I'm trying to show what I have ruled out and how.


Inside my PHSNA: http://www.lysator.liu.se/~mankan/phsna/phsna_inside.jpg


I have a homebrew standalone RF power meter based on https://sites.google.com/site/lofturj/ad8307-power-meter but with an cheap Arduino instead of a expensive Teensy. It is calibrated against a sine signal generator at work at 10MHz and turned out be fairly linear.


I've also built a 10MHz Square wave generator according to Todd(QrpHomebuilder) and Bob(K3NHI) and a simple resistor based step attenuator 0-31dB.


The step attenuator is swepth with a VNA at work and has the following values at 10.1MHz:










I've tested my 10MHz square wave generator together with the step attenuator and the RF power meter.

http://www.lysator.liu.se/~mankan/phsna/standalone_square.png


That was some equipment background, next I tested the PHSNA RF power meter. I built it the same way as in my standalone version, without op-amps but this time I used 2.5V to the Arduino Vref pin.

http://www.lysator.liu.se/~mankan/phsna/phsna_rf_square.png


So, it seems the PHSNA RF power meter section is ok. Now on to the PHSNA signal output.

Measurements with the standalone RF power meter:

http://www.lysator.liu.se/~mankan/phsna/sweep_standalone_rf.png

 

And with the built in one. Note that I have not really calibrated the slope/intercept values.

http://www.lysator.liu.se/~mankan/phsna/sweep_phsna_rf.png

What could cause the dip between 33-42MHz?


And besides that, is the output variance ok?


Br

Marcus, SA5PMG


Marcus Gustafsson
 

Some debug done, I terminated the output with 50Ohm and connected a BNC cable to RF detector with clips in the other end and measured my way back by sweeping with PHSNA.exe and found that is already after T1 I have the dip in the signal.

Steve, you might have been spot on from the start :-). I'll try the bifilar winding but how would I do the center tap which I assume that I should ground? Do I wind 12 bifilar turns and then just cut the primary winding in the middle and ground it?

Br
Marcus, SA5PMG