First of all, congratulations for testing and improvement of 24GHz Wavelab xvrt.
Regarding signal to noise ratio, it is hard to believe about RX performance differences between XP and XN versions. As we know both of them are identically and according HMC967 datasheet the internal gain is almost flat between 500-2500MHz IF. Let's suppose some differences of balun loss and TQP3M9008 gain at 432MHz / 2364MHz. I did some simulations of NF and is almost same in both cases because the "NF/Gain ratio" of HMC967 is high enough to dominate the global NF.
The issue can be related to poor performances of 2364/144 transverter, poor phase noise, poor image rejection, parasitic oscillation or something else. Also the phase noise of XP 1st LO "DSN-2300 PLL" is not excellent, the phase detector and loop filter were designed for 250KHz phase detector reference. Probably Adam-Pluto fractional PLL (AD9363) is superior. Moreover the phase noise is great affected due to x12 Wavelab LO internal multiplication (20log12). You can try to use same LO signal generated by Adam-Pluto for XP xvrt and to check if is any improvement.
It is strange, output level of XP+2364/144 transverter is less than standalone XN. Where is the additional gain of DJ6EP transverter...?
- The test can be little more conclusive if the gain of XN is decreased in front of FT847 for same S8 indication, then comparing the noise floor. FT847 has poor linearity of S-meter response vs signal strength, can be easily confirmed using a calibrated step attenuator.
- More accurate S/N comparison of XP vs XN can be done using a SDR receiver (Pluto?) connected to Wavelab IF RX output and same 1st LO (DSN-2300 programmed to 1807 and 1968MHz).
- One more test can be "minimum detectable signal" by rotating the horn antenna for very week signal and comparing both units.
PS: I have both units XN/XP and i will compare RX performances with my first opportunity.
Regarding signal to noise ratio, it is hard to believe about RX performance differences between XP and XN versions. As we know both of them are identically and according HMC967 datasheet the internal gain is almost flat between 500-2500MHz IF. Let's suppose some differences of balun loss and TQP3M9008 gain at 432MHz / 2364MHz. I did some simulations of NF and is almost same in both cases because the "NF/Gain ratio" of HMC967 is high enough to dominate the global NF.
The issue can be related to poor performances of 2364/144 transverter, poor phase noise, poor image rejection, parasitic oscillation or something else. Also the phase noise of XP 1st LO "DSN-2300 PLL" is not excellent, the phase detector and loop filter were designed for 250KHz phase detector reference. Probably Adam-Pluto fractional PLL (AD9363) is superior. Moreover the phase noise is great affected due to x12 Wavelab LO internal multiplication (20log12). You can try to use same LO signal generated by Adam-Pluto for XP xvrt and to check if is any improvement.
It is strange, output level of XP+2364/144 transverter is less than standalone XN. Where is the additional gain of DJ6EP transverter...?
- The test can be little more conclusive if the gain of XN is decreased in front of FT847 for same S8 indication, then comparing the noise floor. FT847 has poor linearity of S-meter response vs signal strength, can be easily confirmed using a calibrated step attenuator.
- More accurate S/N comparison of XP vs XN can be done using a SDR receiver (Pluto?) connected to Wavelab IF RX output and same 1st LO (DSN-2300 programmed to 1807 and 1968MHz).
- One more test can be "minimum detectable signal" by rotating the horn antenna for very week signal and comparing both units.
PS: I have both units XN/XP and i will compare RX performances with my first opportunity.