Experimenting with waveguides using the LiteVNA

[xrunner]

Phono jack for power? Sure as long as you own it it'll be fine. Otherwise better label it or another owner will want to listen to the thing working. 

Photography nice - good presentation setting on the table. Hey what's in the bowl?

[joeqsmith]

I was thinking if I did decide to control the relay, I would swap out the phono jack for a mini DIN.   Mechanically it will fit in that area.   9-pin D would be a lot of wasted space.   I've used phono jacks for power before,  like this amplifier that I used to demonstrate one potential problem when using these low cost VNAs with their squarewave drive.  Note the battery holder is stored with it and the connector is marked.  Even my design scribbles are in the bag.   Just in case after my death my wife holds a big sale and a ham buys it for 5 cents.

The table was made by my grandfather and the bowl and egg shapes inside are Alabaster from Egypt. 

[joeqsmith]

Making a basic checkout, seems no worse for the wear.   So for fun, I connected a decent GORE cable to the converter and attached it to a 23 inch section of that semi-ridged RG402 that I used to wire it with.   At 11.8GHz, I measure about -4.4dB.  No attempt was made to calibrate the system as I was really just interested in a relative measurement.

Next I replaced the semi-rigid cable with one of my unused cables supplied with my V2Plus4.  If you follow the channel, there was segment where my test setup slowly falls off the desk dragging the VNA to the floor by the cables.  These cables are not the ones used.  I had two sets.   These are about 12" long.   Notice I loose about a dB.   

Last, I placed a Weinschel WA3 3dB attenuator in series with the V2Plus4 cable.  This attenuator has a spec'ed frequency range of DC - 12.4GHz.   Like magic, it measures about 3dB lower. 

So the semi-rigid cable you purchased can certainly improve the losses if you decide to go that route but it's a one-shot deal.  Make sure you understand that it is easy to damage, like our friend here learned, and I gave it my best shot at repairing it with no success.   It's also a pain to put together.   

https://www.eevblog.com/forum/rf-microwave/is-is-possible-to-repair-a-hairline-crack-in-semi-rigid-coax/

I ran a few checks of S11 as well and I think we are ready now for some labels....

[joeqsmith]

Here's a stupid test for the fun of it.  It's my spin on the Jim W6LG videos showing how much loss connectors have in the HF bands.   We all know not to use transmission lines beyond their cutoff but I did say stupid....   
https://www.microwaves101.com/encyclopedias/coax-cutoff-frequency

Tuned the VNA to the lower end of the extender and inserted a SMA thru.   No attempt was made to calibrate the system.  Like before, I just looking at relative numbers.   Measure about 0.5dB. 

Next I replaced the thru with 12 BNC adapters, including two SMA to BNC adapters.   Measured about 2.5dB lower. 

Last stuck in a Midwest Microwave BNC attenuator PN# ATT-0313-06-BNC-10 into the mess.   Measured about 9.3dB.   
https://www.mouser.com/datasheet/2/643/pi-CCS-MW-ATT-0313-06-BNC-10-1312565.pdf

Nothing real useful from our Baby N Connectors.  I did qualify with stupid.   

[joeqsmith]

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..

[joeqsmith]

When I first swapped out the directional coupler for something with better directivity, I plotted how it improved the noise floor.   
https://www.eevblog.com/forum/rf-microwave/experimenting-with-waveguides-using-the-litevna/msg4903016/#msg4903016

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. 

[joeqsmith]

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.   

[joeqsmith]

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.   

[joeqsmith]

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.

[joeqsmith]

With the Narda waveguide load attached, about the only thing we can see is where the low frequency cutoff is.   Still, below 6GHZ where it was designed for, it has decent performance and I am not aware of anything else in this price performance range.   

[joeqsmith]

Tried to locate a good condition, used N to SMA adapter for port 2.   They are out there but the high costs made them not worth the risk.   At 12GHz, no point in trying the low cost Chinese parts.  Ended up buying a new Hirose  adapter and called it good enough.

https://www.digikey.com/en/products/detail/hirose-electric-co-ltd/HRM-554S-40/5148329

[joeqsmith]

The work of Jagadis Chandra Bose. 

https://www.cv.nrao.edu/~demerson/bose/bose.html

[joeqsmith]

One problem with playing around with used waveguides is finding data sheets.   Most of the cold war military contract houses are long gone, along with all the information for their products.

I've been looking for a isolator with decent isolation specs.  People who are selling such devices are not typically going to have the means to measure them.  So you are basically going on a blind date.   In this case, looks like I may of gotten lucky.   Using the frequency converter with the LiteVNA, I measured an insertion loss of <2dB and isolation > 26dB.  The low quality transitions were clamped on and I doubt very much the insertion loss is this poor.   

[joeqsmith]

Quartz sample tube, cavity and shims.

[joeqsmith]

My breadboard is getting some use tonight running a temperature test.  Board has about 214mA though it for a few hours.  Transistor dissipates about 2.8W.  Sinks a bit overkill but doubt the breadboard is going to have a melt down at these low currents.

[joeqsmith]

Breadboard was tested up to 400mA and ran for a few days before transfer to perfboard. 

[joeqsmith]

VtoI driving the cavity,  the range is about 1000G.  Cavity has a wide resonant frequency range that it can work in as well.  It will eventually need feedback to minimize the drift. 

[joeqsmith]

Basics on EPR:


Basics on spin:

[joeqsmith]

How to Parafilm,  used to seal the samples.   Hydrates was already mentioned. 

[joeqsmith]

Prepared samples.     

[joeqsmith]

Setup ready for running samples.

[joeqsmith]

Another basic video describing EPR/ESR. 

[joeqsmith]

Much better video on quantum mechanical spin:

[joeqsmith]

Attempting to run a different chemical tonight.   

This little home project has once again shown me just how ignorant I am.   Planning to put some sort of video out, but rather from a physicist's point of view, it would be from a EE who knows jack all about the subject.        

[joeqsmith]

The frequency drift needed to be addressed.  I modified one of my original LiteVNAs to include a external clock reference input.  I was planning to modify the latest revision of the LiteVNA I have but it turned out there appears to be a problem that causes 50Hz dips in the frequency.  I repeated the frequency stability test using my third LiteVNA which is also the older revision of hardware and it also does not exhibit the problem.  While I have raised the issue, I doubt it will be addressed so future tests will be based on the older hardware. 

Shown is the modified VNA.  I pulled the oscillator.  Added an SMA with a TVS and termination.   The LiteVNA requires the clock to be 24.0MHz.  For now, I am just using my RF generator to derive it.   With everything now locked to the GPS, we can measure the resonance of the cavity over an extended time.