Experimenting with waveguides using the LiteVNA

[joeqsmith]

I mean the samples could be hydroscopic and I believe water effects that quite a bit.

Yes, by definition the hydroscopic sampled would indeed absorb water.

A while back you had mentioned a spectrometer project. 
https://www.eevblog.com/forum/rf-microwave/experimenting-with-waveguides-using-the-litevna/msg4844993/#msg4844993

Doing a quick search,  ChristofferB from Denmark had started several threads scattered over several years but failed to show any results.  I have complied a list of their threads to make it easier to located.   You appear to have engaged in a few of them but I never saw you post about any hardware.  ChistofferB hasn't posted in a few years.  I checked out their YT channel but it's been a few years since they uploaded anything.  Have you actually attempted to replicated such an experiment?   Consider posting about it if you have.   

May 2017,    https://www.eevblog.com/forum/rf-microwave/x-band-transparent-stick-for-diy-electron-spin-resonance-spectrometer/
Sept 2017,   https://www.eevblog.com/forum/rf-microwave/diy-epresr-spectrometer-general-overviewdummy-load/
June 2019,   https://www.eevblog.com/forum/projects/annealed-cast-iron-as-magnet-pole-pieces/
June 2019,   https://www.eevblog.com/forum/projects/diy-nmr-(nuclear-magnetic-resonance)-spectrometer/
Aug 2020,    https://www.eevblog.com/forum/rf-microwave/x-band-cavity-design-and-microwave-safety/
Dec 2020,    https://www.eevblog.com/forum/rf-microwave/microwave-frequency-response-like-its-1971/
March 2021,  https://www.eevblog.com/forum/projects/diy-nmr-best-way-of-driving-a-swept-magnetic-field-between-two-solenoids/

I had read a paper about Zavoisky after reading Southworth's book.   He was a ham and thought, hey, what if...  Interesting project. 

[joeqsmith]

I had tried a few different experiments using the waveguides and VNA to look at how different stuff around the house absorbed RF.  This was the previous jigs.   I was trying to see if I could use the T as a bridge to compare vapors with air and detect a difference.  That was the use of the Kapton windows.   

While I have some data I could post if you would like to see, seems rather pointless so far.   No plans for any videos just yet.

[coppercone2]

not even close, I am still waiting for the wave guide parts I put in a month ago to show up from the other side of the planet, and then I expect a 2 month delay to send back the incorrect wave guide parts that were sent to me   

and hopefully I will be distracted by the 18 month tig welder fix I think I achieved, the silicone conformal coat came in today and I washed all the transformers etc so maybe I can put that machine back together, inspect the solenoid, measure some crimps and finally try some welds

and for chirsb, I bet 99% chance IIRC he was working on the same thing at work. do the same thing at work and at home and your gonna stop working in either work or home because its just too much. if its well funded you end up feeling like you are trying to replicate a cost sensitive version of what you are doing at work at home and that is not that interesting for most people IMO, or the opposite if your boss is mad greedy and you figure out you are jumping through hoops and playing games at work because a few things are 'neglected', and then its like time to turn the brain off before I figure out how bad the situation really is

or #3, you actually might invent something and get burglarized by a corporate lawyer because of that thing you signed that loosely states you invented it because of the company and you don't have the legal muscle to defend yourself, even if its some irrelevant crap that they tried once like 10 years ago and forgot about until they saw you make money

[joeqsmith]

There is that one salvage yard I posted who has a large assortment of waveguide parts.  The problem, they do not provide any details about the dimensions.  If I lived in the north east, it may be worth a road trip just to go though their inventory with a micrometer.   

A neodymium magnet next to the cavity and iris.  The nuts, cap screws, spring are all stainless.  A lot of copper, brass and silver.  The only thing ferromagnetic is  the ground shaft of the Sterritt micrometer.   

With the limited travel and the micrometer, compared with the old HP adjustable short, it's much easier to tune.   There is also very little backlash, unlike that 1950s HP part. 

***
When I first started out, I did not have to sign an NDA.  I remember reading about two soft heads that worked for TI that had taken home the software they were working on.  TI got search warrants and then sued them both.  Their defense was they found the work interesting and saw no harm in taking it.   Now days, it's more like this:

[coppercone2]

did you get the rotating or non rotating head micrometer? Probably does not matter. I mean the starrett that has a key in it so the shaft does not spin and just presses

[joeqsmith]

There's an old Varian water cooled magnet on eBay if you're looking.    I tried to find some data on it but no luck.   2 Tesla?  3? 

https://www.ebay.com/itm/371320266536?hash=item5674699f28:g:PtcAAOSwqu9VR--D&amdata=enc%3AAQAIAAAA8FoscPmUaJO22bDxvDTmFxI5XuPxCHyvkIXzN0m82qg1SiugPbVzwPAEwGElT98IjwSzsJoC0B8nyQbAJP6Tg91%2BJ%2F0Gc2mEIhBFemDEqrjtyFDWMuPy8VDwmRhj2LTnjXdhUdyC%2Fj9Afc5XHslaIPaJkGOjrmC2nrSZ1ssktzLLegFgTvzAS5GPCZ9r7dhdC%2Fsf%2BHV9HEjk2z%2BaIimZWZ4di1wyc2d04kIXNEQkRmZL9iwxllv7JqShbw1xD8g8Za%2FedlB9T3Y6amhdj7X6MQyQmzx1x%2FQeECNlYgNvU0tarm1Pm5%2BHjlSpJoWxBequXg%3D%3D%7Ctkp%3ABk9SR7DlwceMYg

[coppercone2]

lmfao need a fork lift first

[joeqsmith]

I imagine the power supply and other equipment that went with it at least doubled the weight.  Your friend ChristofferB was talking about using the X band.  I assume that was partly due to the lower field requirements.  Old though, I never saw once where they measured the field or showed the sweep in operation.   Maybe they were further along than I was able to find but it seemed like more a 4 year thought project.   

[coppercone2]

well I think he is a grad student iirc so the project budget may have been diverted to basic essentials

[joeqsmith]

That last post I had found, it seemed like they had ditched the original idea and started to go in a different direction.  A few people chimed in, including yourself but that was it.   Their signature states "Chemistry phd student!"  but I assume by now they would have graduated. 

When they increased the frequency, I assume they knew they needed a field 3X.  But I didn't get the tiny little coils they show having near enough to get the offset they would need.  Maybe. 

[coppercone2]

Oh, lol maybe they got a old one when the first job company replaced the older one to keep their yearly budget

[joeqsmith]

Or they eventually realized it wasn't as easy as they first thought and cut their losses.   

[coppercone2]

well every picture I see of those x band type machines they require a fork lift for installation. I never really bothered to figure out what the magnet would look like, I just put the project on the back burner because I figured something ugly would present itself there in some form.

I do like the high current low voltage circuits though, but the biggest I went is that 2000W resistance brazing transformer, though for all its worth I suspect that if I just figured out how to use that in all its capabilities to save on acetylene it would just come back to haunt me when I forget to exercise the gas valves and I need to replace baffles and shit because the tanks go unused for too long. And the wires are too damn heavy,. rather use the 'light' cobra torch, I start thinking of arnold swartsnegger when I wire up that vutron super 0000. That little spot heater I cobble together makes you feel like you are a power loader. I just need to strap the transformer on my back and replace my hand with a large knipex pliers wrench and I am ready for work.... that would be a good exo skelleton too, two pliers wrench hands connected to giant current transformer so you can heat bend I-beam and shit.

tldr: holding objects with heavy hoses or cables makes you feel like a robot

[joeqsmith]

There is a display of Zavoisky's lab where they have some of his original magnets.   It appeared that ChristofferB was planning to use a combination of fixed magnets and pole piece to get the minimum field, then use a coil to make up the difference and allow them to sweep it.   This would really scale down the size and power required.   

[joeqsmith]

I tried an on-line calculator to pick some magnets but in the mean time, I took a couple I had and placed them around the section of WR90 as shown.  The center of the guide measures about 1900 gauss.   I calculated what I would need for a coil but for fun just chopped up a solenoid I had and set the gap to roughly a half inch and got about 500 gauss in the gap.  So, it does appear that we could make a programmable field that wouldn't require a lot of space or power to run it.   I would need to add support to my software to control a power supply to drive the coil but that would be trivial.

[joeqsmith]

Attempt to 3D print copper and sinter it.   Interesting idea but doesn't look like we can pull it off with our setup.     

[joeqsmith]

Still looking for a better coupler to replace the old Narda part I have been using to measure S11.  The Narda 3095 looks like it would be a good fit.  Cheap, covers the X-band and good directivity.   These use the APC7.  There are some <$15 USD from China.  Searching this site, someone had asked about them a few years ago but I don't see any data.  They advertise them good for 6GHz.  Wonder how they perform at double that frequency. 

https://www.eevblog.com/forum/testgear/apc7-to-sma-adapter-from-china-ok/


Cheap APC-7 SMA adapters from China.
https://www.ebay.com/itm/314581375697

Datasheet for couplers
https://nardamiteq.com/product-spec/097-Couplers.pdf

3096, directivity 25dB
https://www.ebay.com/itm/304867686545

3095, directivity 33dB 
https://www.ebay.com/itm/304898554282

[coppercone2]

Wow you can sinter with a extruder printer?

I am guessing its a high copper content 3d print wire that is then baked in a kiln for burn out and sintering?

I am just waiting for my ground cable to come in for the tig lol, got the wrong gas lens in my kit so I only have the quartz one.

I think usually they say that out side of the frequency band of operation for the next octave you might be able to find a stable narrow region of operation that is potenitally usable in spite of the 'modeing' that occurs. But I have no idea for the band under. I think its potentially usable at a higher frequency for some small random bandwidth, but not with the lower end.. that is a hard cut off I think? Wavelenght too small for wave guide = odd transmission modes, wavelenght too big for wave guide =? (I think its very high reflection but not sure)

from what I understand : the most out of bounds components you have (operating past their max frequency) the less likely you can find a useful transmission band, since each component might have a random area that transmits some frequency but they are not correlated so with more then 1 component you might not have a path through.

[joeqsmith]

I would say we tried to sinter with an extruder printer.   Yes, as you described.

All of the parts for that extender are fine for the X band now, except that coupler.  Even at 11GHz, it works better than I would expect but this is really the problem.   The mixer's IF is limited to 4GHz but right now, I can't even sweep up that high.   

https://www.eevblog.com/forum/rf-microwave/experimenting-with-waveguides-using-the-litevna/msg4850513/#msg4850513 

Thinking I may add in that terminated SPDT relay as well so we don't have to move cables.   Eventually, it needs to get mounted into a box but for now I'll leave it as a 3D mess. 

[joeqsmith]

Try finding couplers with over 25 dB directivity.   They are not common.  I want to keep the coupling at 10dB and plan to give up the half dB loss by leaving it in-circuit.   HP offered the 33311B relay with a 5V option.  It seems like it would be a good fit.   

https://www.ebay.com/itm/144419029196

[coppercone2]

here is a 50db coupler
https://www.everythingrf.com/products/waveguide-couplers/flann-microwave/228-248-16133

hidden behind a quote wall.

it appears they are quite long for higher directivity

A 779D or similar is like 30dB.

https://www.romtekonline.com/product-details/multihole-directional-coupler.html
35

might be worth checking the Flann brand out on ebay, they seem to be all that shows up for higher db directivity

https://flann.com/wp-content/uploads/2015/09/Flann-Final-2015-for-Website-Use-06082015.pdf


your finger sir
https://www.ebay.com/itm/175741081773

[joeqsmith]

I would have thought you would understand that everything on the extender is coaxial.   That said, it would certainly be possible to make it all using WGs, if size, availability, cost, ease of use.....   

[coppercone2]

nope I read that in between trying to clean this p6015 probe for silicone oil with all the high cleanness procedures and totally forgot, at least i did not spill hot oil anywhere yet

I am suspicious that the silver plating on the high voltage resistors disintegrated into the freon or something, there was alot missing on the resistor. I wonder if that could make it arc over

[joeqsmith]

When I designed that wideband HV probe, I didn't want to use anything liquid.   So ceramics and make it large.

[coppercone2]

I saw your point because of thermal expansion and also bubbles. I was gonna squirt a little bit of butane in there before sealing though, just a drop...

might just have to say... avoid probing awfully low impedance circuits. For limited HV stuff, it should just spark inside of the tube. Would I trust this for probing a HVHC transformer.. nope

kinda wonder what CAT rating this probe would have with freon, with oil, and then the proper redesigned one with oil in it.

Kind of think that a very high current high voltage probe that can explode, should have a HV fuse in front of it, whatever that looks like. Or because of bandwidth reasons, a minimum safe distance... ship it with a tape measure....