Sweep output debugging [2 Attachments]



Your double peaked plot reminds me of one that I did with my PHSNA, which shows a deep dip around 30 MHz.  The reason was a cable that connected  it to a high impedance RF voltmeter and was in parallel with the PHSNA detector.  It was 123 cm long and in fact it was working as a parallel open stub and the PHSNA shown its resonance.
I also attach the plot without the open cable and a sweep that I did during the calibration, showing how well the polynomial correction worked.
My PHSNA does not use The Type II DDS Chinese board, but a DDS-60 so it does not need the transformer. 
Some toughs about the problem:
Did you removed the filter components onboard the DDS?
I think that you may be double loading the transformer, hence the DDS.  If you are loading it with 50 Ohm and at the same time using the power meter (either internal or external) you have 2 50 Ohm loads in parallel.  If you are using an external high impedance meter at the end of your test cable, you are seeing the cable.
If you have access to a signal generator, manually sweep the transformer with a load at the proper side.  I have had problems with wrong cores.
I hope some of this may help.

73 de Ignacio EB4APL

El 19/02/2016 a las 21:19, mankan@... [PHSNA] escribió:

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?

Marcus, SA5PMG

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