Electronics > RF, Microwave, Ham Radio

Experimenting with waveguides using the LiteVNA

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Been waiting to run this test because the SMA wasn't yet secured to the front panel. 

Connected the extender directly to my microwave counter and set the LiteVNA to 500MHz CW.   The PDRO is at 7.86G (just below the X-band).  We should measure 8.3600000GHz but the counter measures 8.360019671 and it's hunting....... Imagine that...

Connecting the extender to the 10MHz GPS reference,   get the counter measures 8.359999964 and is stable within a count.  The rest of the error is the LiteVNA's internal clock.  Too bad the VNA doesn't have a reference input as some of the experiments I was attempting, the VNA's drift comes into play. 

Good to see it all working again.  Time to clean up the mess..

When I first swapped out the directional coupler for something with better directivity, I plotted how it improved the noise floor.   

You can see there are some areas where you can get much better dynamic range than others.  Attached for example, running some attenuators from 0 to 70dB to get an idea of the linearity.   Finger tight and normalized thru.  Mix of my very low cost Chinese attenuators.    Typically its going to be around 50dB and worse case looks like maybe 40dB assuming 10dB headroom.    Not great by any means but far better than trying to use the harmonics at 12GHz and good enough for my home experimenting. 

I did try repeating an earlier test stacking some 10dB MWM attenuators in series.  These are still just jelly bean parts but a bit tighter tolerance.  Parts were torqued.  For the 3 and 6 dB, I used two other name brand attenuators I had.   This is really about what performance I expect out of it.   

Running a SOSL cal with my homemade standards and measuring the return loss of the terminator supplied with the university microwave trainer.   Swept it from 7.9-12.5G just to get a better idea how it performs.  Not great but cheap. 

Note the three sets of data are from my original PCB construction prior to the new case, and with both the old and new directional coupler.   

Using Dislords firmware, the LiteVNA supports I think unlimited harmonics, or at least way beyond what is useful.   If I wanted to measure S11 directly rather than using the frequency extender,  at least for the X-band and my particular versions of hardware, we can't.   Using the supplied cables, short, open and sorted mini-circuits load to calibrate the VNA from 1M to 9GHz.   Plot showing the return loss with the standard attached.   Even at 9GHz, the return loss is basically 0.


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