cheap THz experiments? - Page 1
Forum section: electronics / rf-microwave

author: coppercone2
author_rank: Super Contributor
timestamp: December 30, 2021, 08:08:23 pm
content: So I was trying to think of something fun and new for the next year, and I was wondering about diode detectors.I bought castable 3d-printer resin recently, which would allow me to pour any shape I want, within reason. I see there are no problems making fancy geometry rings and such on youtube.This makes me believe I can cast waveguide or antenna parts out of silver. Yes, somewhat expensive, but not as expensive as THz electronics. Combined with the silver-on-ceramic PCB methods that I discovered recently, it seems plausible to make some kind of circuit, i.e. a detector coupled to a horn in order to try to pick up THz emissions from a silicon carbide glo-bar source.I also noticed that most diodes (i.e. conventional diode), is actually very small, for instance ceramic zener diodes, if you crack them open, they have something like a grain of sand sandwiched between two copper cylinders. If I was careful on some lapping media I could make that diode shorter. I believe I read that even normal diodes have a rather wide bandwidth, thats not including 'shortened' diodes, or really small diodes (i.e. 0402 or smaller).Does anyone have any inspiration for this line of projects? If I cast the right size cavity and horn could I correctly position a modified diode to make a reasonable THz detector?I am tired of being bared from this electromagnetic region because of financial reasons. I think I can make a glo-bar and I think I can make a cavity/antenna, I just need to know about the detector element in the systemThermal Imager/Optics forum version of threadhttps://www.eevblog.com/forum/thermal-imaging/mmwaves-optical-methods/msg3929741/#msg3929741

author: cdev
author_rank: Super Contributor
timestamp: December 30, 2021, 08:48:11 pm
content: I am also interested in this. I have access to a back yard. I think that outdoor environments have an advantage of being fairly free of reflections. One possibility is building a robotic platform to rotate an antenna in 6DOF. and then receive the signals a bit of a distance away and detect and record the RF signal strength, and perhaps a video of the view along the antenna's primary signal axis. (showing what direction it was pointing in)This would be extremely useful in developing antennas.You can also use satellites as signal sources with known locations.

author: coppercone2
author_rank: Super Contributor
timestamp: December 30, 2021, 09:41:51 pm
content: Yeah, I am pretty confident it can be made. I think someones post somewhere on this site said common diode had like response to 90GHz or something. But I can't find it.If you can cast it you don't need a multi-axis cnc machine to make the horn feed or anything like that, and its small enough so you can make it out of solid silver for not too much cost. Vacuum casting would be the best. The geometry of horn feeds is obnoxious.Any candidates for misused diodes or transistors as detector elements? A simple power detector would be the most logical first step I think.

author: Joel_Dunsmore
author_rank: Regular Contributor
timestamp: December 31, 2021, 04:23:13 am
content: not to rain on anyone's parade (PS, THz don't go through rain much either), but THz is really a challenge. I've been doing a lot of work in the D-band (110-170 GHz) and some up to 330 GHZ, and everything is hard, and fraught with trouble. You don't need to be outdoors for antenna testing as far-field is something like 10 cm, even for a large phased array. And you don't have to worry about re-reflections as free path loss is something like 73 dB per meter at 110 GHz. The thing that kills anything operating at these frequencies is shunt capacitance. The capacitance for a corner freq of 110 GHz is on the order of 30 femto-farads (0.03 pF) so smallness is definitely your friend.

author: 0culus
author_rank: Super Contributor
timestamp: December 31, 2021, 05:17:15 pm
content: Quote from: Joel_Dunsmore on December 31, 2021, 04:23:13 amWhat sort of equipment are you using for your work up there? If you can't share exact setups that's fine, but I'm curious what's on your bench, so to speak.

author: coppercone2
author_rank: Super Contributor
timestamp: December 31, 2021, 05:53:21 pm
content: I bought a bunch of diodes that claim to go into the high regions (fractional THz). I think you can just shrink a conventional waveguide diode detector down.What makes a good detector diode anyway?What I was thinking if you liberate the actual diode that is inside of a conventional cerMELF package, it is literarly the size of a grain of sand. You can wedge this into a cavity of some kind to make a electrical contact I think (i.e. grind a tiny jacobs taper out of one side of the diode copper contact that is 1000x times bigger then the diode). What if you press fit the copper contact of the diode so the diode is flush with a cavity (cold fit). That should make the package transparent I think?I know its gonna be shitty but I would need to turn into a real big wig to try to even get that gear on a clean financial conscious.Is that not an amusing image? BTW Props on building a enclosure for a test system! inconceivable. Now the secret is they need to be lego man sized.

author: KE5FX
author_rank: Super Contributor
timestamp: December 31, 2021, 07:59:50 pm
content: The people doing the most interesting work at this end of the spectrum are probably the NRAO folks and their international collaborators. Some great papers and tech studies came out of the ALMA project in Chile, and are well worth tracking down.Darrel Emerson's essay on J. C. Bose and his early mm-wave work is also a must-read, if it's still online.

author: jjoonathan
author_rank: Frequent Contributor
timestamp: December 31, 2021, 08:05:00 pm
content: Quote from: 0culus on December 31, 2021, 05:17:15 pmSince Joel probably can't give us details very far beyond what is publicly available at theKeysight mm-wave VNAsite, allow me to speculateThey are working on a PNA-GTX with turbocharger. It does to 0-150 in under a second (GHz, of course), it has flame decals on the side, and the fans make "vrooom" noises that scare small animals. It finally does away with the three-box design (base VNA + mm controller + sample heads) in favor of just having small probe-size sampling heads that plug in to the main body. Different probes are available for different connectors / frequency ranges. To be announced in 2022, but none of our employers will be able to afford it until 2025.------------Regarding janky home setups, though, I have to warn about expectations on SLA printers: accuracy and repeatability offer rude surprises coming from the world of machining, even janky home machining, where the usual rule is that you can do .010" without thinking, .001" with care and good technique, and .0001" by really dialing things in and sweating the details. Controlling for time, effort, and experience, cheap equipment sets you back half an accuracy class. 3D printing sets you back 1.5 accuracy classes.You can get to within a few thou, but you'll have to bust your butt to make it happen. The exposure process grows/shrinks your part as a nonlinear function of geometry, temperature, humidity, resin type, batch of resin, how well mixed the resin is, etc. It's not a problem for printing D&D figurines, but it's a big problem for engineering... which explains the relative adoption of 3D printing to the two applications. For a while I used a chart to map hole sizes modeled vs actual (test part + pin gauges + patience) but after controlling so many variables and still seeing the plot hop around, I basically gave up. Every time I need accuracy on a print I resign myself to the necessity of iterating a few times or post-processing. It's like going back in time to before the interchangeable parts era. I've had 10x less trouble and better results compensating the deflection in a cheap cnc aliexpress router, and that's really saying something, because those aliexpress routers are themselves floppy garbage.Oh, umm, and be sure to get a printer with linear rails. They are cheap these days. Everything bad I said applies to the ones with linear rails, but the ones without rails are even worse, because the build platform deflects due to stiction and makes the parts wavy in addition to the usual problems of over/underexposure, potato-chipping when drying, potato-chipping over time, elephant foots, and chicken skin.Of course, if you're willing to relax expectations it's fine. If you just want to see a signal, what are a few dB, or even tens of dB? If you just want one working sample, a few iterations will absolutely get you there. Keep the rat-tail files handy, stay patient, and sneak up on those dimensionsOne thing is for sure, it will be an adventure!

author: 0culus
author_rank: Super Contributor
timestamp: December 31, 2021, 08:07:39 pm
content: Quote from: jjoonathan on December 31, 2021, 08:05:00 pmOK, that's hilarious!

author: coppercone2
author_rank: Super Contributor
timestamp: December 31, 2021, 09:57:36 pm
content: hmm well for some things I can see using some kind of broaches etc to clean it up (waveguide) but yeah I expect high losses and its just supposed to be some kind of detector.

author: jjoonathan
author_rank: Frequent Contributor
timestamp: December 31, 2021, 10:20:59 pm
content: Yeah, I can't wait to see the results!A while back MACOM bought what was left of Metelics and their THz line is here:https://www.macom.com/products/diodes/thz-diodes. I vaguely recall seeing some of them on eBay for prices I considered in-reach. I don't think I've ever seen Virginia Diodes products "in reach," but I haven't been aggressively looking either.I know that there are a ton of special fabrication techniques to optimize diodes in this frequency range, but I don't have intuition for just how much you would sacrifice by going without. Is it just a 10dB suboptimal response? 30dB? Do they not work at all? I think you're on the right trail chasing Bose and NRAO for the "scrappy startup" type techniques. Of course, I'll still tune in for any Keysight announcementseven if I can't be an early adopter.At the moment, I'm content saying "my eyeballs are the only THz detector I need," even if that's cheating

author: coppercone2
author_rank: Super Contributor
timestamp: December 31, 2021, 11:13:36 pm
content: How do you feel about the high GHz russian diodes on ebay?I.e. 200GHz pin diode ?Can a Pin diode be used for this?I am curious about the quality of the castings I can get, the best quality would be silicone rubber vacuum casting silver, but that is getting kinda fancy.If you want to use broaches or other odd cutting tools smaller would be better I think since its easier to fabricate smallish tools, there is probobly a sweet spot for every machinery setup that would need to be found... but I did get my hands on a depth micrometer which might be kind of nice for this.ALso, about propagation modes... can circular wave guide be used OK for a detector? I.e. just a tube. Do you need the square geometry for such a primitive device? I did get some arco laps too.. I would prefer to avoid angles as much as possible. Please let me know if I can cut any corners, literally.I was hoping to get between 0.1-0.4 THz. That MACOM thing looks promising but for 1THz I guess you would need to really tune the manufacturing process down... as usual its probobly better to work in steps then shoot for the gold on a wobbly table.I also wonder if casting quality can be improved, when you pour the cast around the wax blank, if you put it in a ultrasonic cleaner for a while to act as a vibrational compacter for the plaster.Also wonder what happens if you try to rumble a molten casting that is cooling down. cavitation would be bad I guess

author: Joel_Dunsmore
author_rank: Regular Contributor
timestamp: January 01, 2022, 01:53:45 am
content: Quote from: 0culus on December 31, 2021, 05:17:15 pmI've use the two American producers of mm-heads (VDI and OML), there are two others as well. Lately mostly VDI with up/down converters as well as mm-wave extenders (they are actually 2 different kinds of modules). Doing things like measuring phase noise at 144 GHz, as well as modulation quality (on the order of 1 Gsymb/sec also at 144 GHz). And with Suren Singh (a.k.a. Mr. Keysight Millimeter), been trying noise figure measurements at 110-170 and struggling a bit at 320 GHz. Y-factor and cold-source. It takes the better part of a day to setup, calibrate, verify, test the DUT, and verify that the test results make sense. And almost every test setup has something wrong with it, so tear down, figure out what you did wrong (Isolator in backward, calibrated a power so low that broadband kTB noise dominates, loose screw on the waveguide flange, power off on the NF pre-amp). All those tests were with PNA-X (yes, it has a baseband AWG in it now). Doing a little work the the new UXA and also UXR as IF receivers for mm-wave down converters. Might have a paper in the fall on the world's lowest EVM measured at 144 GHz if I get myself sufficiently motivated.A little more specificity: I use a N5245B PNA-X 423 with the extra 13.5 GHz rear panel option XSB source that also supports now Arbitrary Waveform Generation 10-6000 MHz. I generate a 1 GHz QAM centered at about 5 GHz with that, and then use the VDI CCU WR6.5 mm-up converter to generate a 144 GHZ output. The PNA internal port 1 or port 3 is used for the VDI LO; then a VDI CCD is used to down convert. I put a waveguide attenuator in the path to make sure the CCD is in the linear range and use the down-converted output to the PNA port 2 ; where I measure and pre-distort the XSB source to get the lowest possible EVM. then I insert the amplifier under test into the path and I can record the EVM of the amplifier+CCD, most of which will be from the amplifier. Oh, and you need a band pass filter on the CCU output to select the proper carrier sideband out of the CCU, if you use the same LO for the down converter; or you can use another one of the PNA sources to generate a different LO so the image doesn't down convert in-band.I've done the same setup with a Marki MMIQ mixer up to about 100 GHz, but in that case I use N5291 system as the down converter.N5291 is spec'd to 120 GHz but you can push it to 130 GHz if you hold your mouth right. Then I can use it to cross-check my results that I got with the external D-band converter in the 110-130 GHz range. Then I spend a day trying to figure out why they aren't the same.

author: 0culus
author_rank: Super Contributor
timestamp: January 01, 2022, 02:25:55 am
content: Quote from: Joel_Dunsmore on January 01, 2022, 01:53:45 amNeat stuff. And one expensive lab bench.

author: Joel_Dunsmore
author_rank: Regular Contributor
timestamp: January 01, 2022, 04:27:53 pm
content: yes, a bit dear.

author: jjoonathan
author_rank: Frequent Contributor
timestamp: January 01, 2022, 07:31:55 pm
content: Wow! Nice! Thanks for sharing! That's some crazy awesome kit -- and research activities to match!It's wild to think of the UXR as an IF receiver, and even more wild to consider that it has higher frequency range than the UXA, and not by a littleI see that ENOB becomes a challenge with mm-wave oscilloscopes -- how much can process gain typically claw back in this application? Close to the theoretical amount or does something else become limiting?Re: Marki MMIQ, are we talking about harmonic mixing on the MMIQ-4067L? I'd be really interested in hearing tips and tricks on this, since I've been doing a bunch of 3rd harmonic mixing on MM1-1467L. I suppose nobody ever told me I was allowed to use odd LO harmonics on mixers designed for fundamental mixing and I'm still a bit caught up on that even though the results are in and it seems to work just fine -- I got a lot of awkward silences asking around about it. The story is straightforward (diodes clip, odd harmonics appear), the Henderson model says it should work for a very modest 10dB penalty, spur tables say it should work, and it does in fact seem to work. It would still be comforting to hear that it was a respectable thing done by respectable people in respectable settings, lol. Also, if you are doing it with a quadrature mixer, and on non-CW signals with distortion requirements, those are two levels of sophistication beyond what I've been doing and it would be nice to hear that it works in that regime as well.

author: 0culus
author_rank: Super Contributor
timestamp: January 01, 2022, 07:46:33 pm
content: I am just happy with narrowband microwave work! Regardless, it is very cool to see a glimpse of the state of the art.

author: coppercone2
author_rank: Super Contributor
timestamp: January 02, 2022, 04:36:48 am
content: sounds about right, I had similar experience trying to learn microwave with non PCB components. Always a problem. At least its fun, until you have to unscrew n connectors too many times, or drop something. (much more simple characterization then yours)At east with MMwave you have small threads, I swear I tweaked my hand before with too many n connectors.

author: 0culus
author_rank: Super Contributor
timestamp: January 02, 2022, 05:04:34 am
content: Quote from: coppercone2 on January 02, 2022, 04:36:48 amYeah no kidding. I ordered a 20mm 8 in lb torque wrench. It'll mainly be used for when I need to tighten the test port NMD connectors on my test set, but it'll come in handly for N connectors too.Also I can only imagine how careful the connector hygiene would have to be in Joel's lab. The tiniest micron of dust will probably upset the whole setup.

author: coppercone2
author_rank: Super Contributor
timestamp: January 02, 2022, 05:10:44 am
content: If they had like a 5 inch knipex syphon pliers for knureled connectors I would buy it. I should get knipex parallel jaw mini pliers wrench too.I would recommend assembling that in a dust free hood actually.. if its that sensitive.

author: 0culus
author_rank: Super Contributor
timestamp: January 02, 2022, 05:22:05 am
content: Quote from: coppercone2 on January 02, 2022, 05:10:44 amOr you just work in a clean room.

author: coppercone2
author_rank: Super Contributor
timestamp: January 02, 2022, 06:18:19 am
content: unless its low level people would HATE that. No one wants to put on that suit.But, can it really be worse then optics? I figure any of these technologies is more dust resistance then actual light.

author: 0culus
author_rank: Super Contributor
timestamp: January 02, 2022, 06:32:41 am
content: Quote from: coppercone2 on January 02, 2022, 06:18:19 amI think it might be worse than optics...a fiber or something stuck in a center pin at these frequencies will cause madness, mayhem, and confusion for the impedance of that connector. This would be less of an issue with traditional optics experiments I would guess.

author: coppercone2
author_rank: Super Contributor
timestamp: January 02, 2022, 06:38:52 am
content: True they are so small the fiber is physically large compared to the contact, I guess light might still pass through but not a conducted signal.

author: jjoonathan
author_rank: Frequent Contributor
timestamp: January 02, 2022, 04:33:33 pm
content: Speaking of soft wrenches, I've been playing around with the idea of 3D printing them. The major challenge is material strength -- even with special high-strength resin and three generations of chunkier design, they still barely work to 1Nm torque. Also, tolerances are a challenge. They need to be snug because sloppiness exacerbates the strength requirements, but "snug" fits just aren't something resin does well. You have to really dial it in, but then a resin change or temperature change or humidity change throws it right back off.I've had a lot more success with "wrench stands," as the geometry is better suited to provide strength. They have a more unique value prop, too: they solve the three wrench problem and they chop a degree of freedom out of the alignment process. I've "standardized" on designing them to hold the center of the connector exactly 3cm off the table (or, more recently, chopping block, since my desk is wavy enough to frustrate the process without some kind of surface plate).

author: jjoonathan
author_rank: Frequent Contributor
timestamp: January 02, 2022, 04:42:23 pm
content: Suhner clicky wrench is still MVP

author: Joel_Dunsmore
author_rank: Regular Contributor
timestamp: January 03, 2022, 01:58:06 am
content: Quote from: jjoonathan on January 02, 2022, 04:33:33 pmNASA designed one, should be too hard to modify adding a open end 5/16. Here's the thingiverse version:https://www.thingiverse.com/thing:608397

author: Joel_Dunsmore
author_rank: Regular Contributor
timestamp: January 03, 2022, 11:05:08 pm
content: Quote from: jjoonathan on January 01, 2022, 07:31:55 pmI realize now I might have been speaking slightly out-of-school. Sometimes Christopher Marki (main mixer designer at Marki) sends me a proto or two to test out. It's was like the MMIQ-4067 just smaller, with wee connectors and with a bigger second number. So I was testing it fundamentally mixed. But almost all balanced mixers operate well in 3-rd harmonic LO drive. We typically figure 12-15 dB lower conversion loss, and that is how the Gilbert-Cell mixers in the PNA work above 27 GHz, in fact.We've been using the MMIQ-4065 for several experiments recently, expect some papers to come out on those experiments later this year. I haven't tried it in 3rd harmonic LO mode, but next time I get in the office I think I'll spin up an experiment

author: jjoonathan
author_rank: Frequent Contributor
timestamp: January 04, 2022, 03:10:44 am
content: Nice! PNA mixers are something I can point to if I need to sell someone on the idea.Yeah, when Marki Microwave released their 125GHz quadrupler I figured they were tooling up to fill out their 1.0mm portfolio. Or 1.35mm portfolio -- as far as I'm concerned, those can't arrive soon enough. 1.0mm just takes things a bit far. New wrenches, no "male thru" connectors, and a constant lingering awareness of how if a mechanical accident happens in your setup the 1.0mm connectors will ensure that the damage gets funneled towards the most expensive components. If you need the mode-free operation range, you need it, but I really like the sales pitch of 1.35mm. If only it had more market penetration... or any at all, for that matter.Good news on the option front, though: if MMQ-40125 is any indication, Marki has decided to stay with .009" pins instead of .005" pins, so the Southwest connectors can be swapped. My entire setup hasn't grown into the 1.0mm range yet, so I'm very much in this business -- I'm sure opinions will vary, but mine is that swapping a Southwest connector beats a 1.0mm gooseneck from a between-series connector, at least if you only plan to do it once in a blue moon.I'll keep an eye out for those papers!

author: 0culus
author_rank: Super Contributor
timestamp: January 04, 2022, 04:13:19 am
content: For giggles:https://www.keysight.com/us/en/product/85059B/1-mm-calibration-kit.htmlI wonder, is there a 1mm ecal or are we in mechanical cal only territory? And how long does your $35,000 cal kit last?

author: jjoonathan
author_rank: Frequent Contributor
timestamp: January 04, 2022, 04:31:17 am
content: Ooh free shipping!

author: 0culus
author_rank: Super Contributor
timestamp: January 04, 2022, 04:37:01 am
content: Quote from: jjoonathan on January 04, 2022, 04:31:17 amI guess that's the least they can do.

author: jjoonathan
author_rank: Frequent Contributor
timestamp: January 04, 2022, 05:01:24 am
content: Looks like RCal goes to 110:https://www.keysight.com/us/en/assets/3120-1426/technical-overviews/U9361-RCal-Receiver-Calibrator.pdfEDIT: Ah, but it only calibrates receivers, not VNAs. I could have sworn I heard something about receivers being used in newer VNA ecal architectures, but maybe I just let my imagination run wild after hearing the term. Certainly by 70GHz it seems that ecals start to look a lot less like a switched SOLT set and more like a "well, they're linearly independent enough" set:https://ieeexplore.ieee.org/document/5165942. It's not limited to ecals, of course, but in the mechanical calibration world the gigahertz giveth conveniently sized air lines, offset shorts, and dielectric loading, even as they taketh away ideal opens, so I could understand if overall calibration strategy pivoted in that direction at those frequencies.I suspect material has been written on the subject... and I have a suspicion about who wrote it, toobut that's a search for another day .

author: 0culus
author_rank: Super Contributor
timestamp: January 04, 2022, 05:12:38 am
content: Quote from: jjoonathan on January 04, 2022, 05:01:24 amIs that the same thing as a VNA ecal though? My understand was this isn't a traditional SOLT style calibration, and is intended to be used with signal analyzers and other "regular" receivers to calibrate out the cable connecting you to whatever your experiment is?

author: jjoonathan
author_rank: Frequent Contributor
timestamp: January 04, 2022, 05:31:14 am
content: Yep, you're right! I think I found out where my intuition went off the rails: I watched a R&S video about newpower sensorsthat used receivers, not ecals. Mystery solved!

author: Joel_Dunsmore
author_rank: Regular Contributor
timestamp: January 04, 2022, 07:06:34 am
content: Quote from: jjoonathan on January 04, 2022, 05:01:24 amR-cal is kind of like the Phase-Reference calibrator (such as U9391G ) in that it provides a very well characterized set of of multi-tones (mag and phase are both known) that can be used to calibrate across a span of a receiver such as UXA or UXR. The U9391 produces a set of harmonic tones (typically every 10 MHz up to 67 GHz) so power is quite low per tone, the R-cal can produce a narrow-band (e.g. 4 GHz compared to 67 GHz) focused at some frequency so the power per tone is much high. It calibrates the instantaneous BW across its range, so you can remove mag and phase response. Theoretically one could use it to calibrate a PNA (which uses receivers instead of samplers, just like a UXA) response ... just a matter of a bit of software.

author: 0culus
author_rank: Super Contributor
timestamp: January 04, 2022, 07:48:31 pm
content: Quote from: Joel_Dunsmore on January 04, 2022, 07:06:34 amVery interesting. Joel, if corporate would let you, you should make a youtube channel like Shahriar. I would subscribe in a heartbeat to see you talk about this stuff and provide demonstrations. If anything it's positive advertising to show off flagship gear...

author: cdev
author_rank: Super Contributor
timestamp: January 07, 2022, 02:05:07 pm
content: Here is how to get rid of dust. Brand new leaf blowers and HEPA filtration, and a spiral airflow. (go in one direction so the air describes a circular path in a room.) Use the leaf blowers to dislodge the dust and large size HEPA filtered air cleaners to suck it up. Wear a P-100 mask yourself while you do this, and of course, use HEPA vacuums to clean everthing too. By doing all this you can create an environment with very minimal dust, when you are through. Good for microscopy, etc.

author: Ultrapurple
author_rank: Super Contributor
timestamp: January 07, 2022, 07:47:45 pm
content: Harking back to the original direction of this thread, the OP may want to raise their head in the Thermal Imaging section. Single-digit THz is considered a bit low-frequency there, but you'll find a bunch of people with a different spin on things. And alotof experience.

author: Bud
author_rank: Super Contributor
timestamp: January 07, 2022, 07:56:28 pm
content: Quote from: cdev on January 07, 2022, 02:05:07 pmYou are ef-king kidding me. Go try a leaf blower in the garage first and tell us how it went.

author: coppercone2
author_rank: Super Contributor
timestamp: January 07, 2022, 08:39:38 pm
content: The optical approach to THz is unfamiliar with me but I need to think of some topics.

author: doktor pyta
author_rank: Frequent Contributor
timestamp: January 08, 2022, 07:39:01 pm
content: 'Low-cost THz heterodyne detection by miniature neon indicator lamp glow discharge detector'https://www.spiedigitallibrary.org/conference-proceedings-of-spie/8188/81880P/Low-cost-THz-heterodyne-detection-by-miniature-neon-indicator-lamp/10.1117/12.898035.short?SSO=1

author: coppercone2
author_rank: Super Contributor
timestamp: January 08, 2022, 10:53:50 pm
content: sounds like you can increase sensitivity by using a parabolic reflector or channeling the energy otherwise. If you use a antenna with a waveguide it should act as some sort of filter.Does anyone know like what power level you can expect to receive energy in this band from space?But I got the paper on the neon thing and it looks like you need a 300GHz source.. so maybe the detector is cheap but you still need something very expensive. Maybe neon and a photomultiplier if it glows slightly or something? I think some kind of diode is more practical for the "cheap" part of this. They don't show 'direct detection' at the higher frequencies, they only show it for the lower frequency. I assume that means they had some kind of problems.

author: jjoonathan
author_rank: Frequent Contributor
timestamp: January 09, 2022, 09:49:01 pm
content: Yeah my impression was that detectors were the easy part: I bet you could get a bolometer to workliterallyfrom DC to daylight. DC sees a resistor, RF sees a termination, IR sees a blackbody, optical sees a tiny black strip of material. Energy conservation says that if the power isn't reflected or stored or re-emitted, it's coming out as heat, and if you can detect that heat, there you go.The flip side of that intuition is "RF techniques stop working before optical techniques start working, and everything is super lossy." Diodes become tiny and lossy before SHG and THG crystals start doing their thing. Transistors become tiny and lossy before losses drop enough to make a laser gain medium that actually has, you know, gain.I'm far from an expert, but every year that I see a flurry of papers claiming to bridge the THz gap, I know that the gap is not yet bridged. Once it is, papers will stop claiming to have bridged it. In the meantime, you just have to pick your poison by taking an RF or optical technique and driving it far into a regime where it doesn't work very well.

author: coppercone2
author_rank: Super Contributor
timestamp: January 10, 2022, 03:49:20 am
content: I kind of wonder if maybe rather then neons passing them through some kind of larger field might produce some effects, but it would require a glass shop to even begin to experiment with it. Like large gas devices not optimized for light emission or circuit use or anything like that. Density fluctuations measured with lasers (totally random thought).

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: January 10, 2022, 08:21:37 am
content: Also a millimeter wave and THz guy here. I've mostly focused on D-band, but I've also done measurements at 330 GHz, and assisted colleagues in the design (and mostly measurement) at 660 GHz and 1.1 THz.I think spectrum analysis and signal generation should be doable, provided you can already generate a few GHz at decent power. If you drive a diode with say 10 GHz at 10 dBm, even if the conversion loss is like 50 dB, you get -40 dBm at the 10th harmonic, which is detectable (with another diode in a similar setup) by a good spectrum analyzer? Could start at a few tens of GHz this way and see where it goes.Those who know me might see this one coming, but consider doing experiments with dielectric waveguides as method of getting signal from a to b. A 'cheap' piece of PE rod can work just fine for this to carry signal a few meters with only 10 or 20 dB loss.

author: coppercone2
author_rank: Super Contributor
timestamp: January 12, 2022, 12:56:05 pm
content: another option for the high GHz band might be to use automotive radar.I see the modules are not that expensive.. but I am not sure how much trim adjustment you can do on them.

author: 0culus
author_rank: Super Contributor
timestamp: January 21, 2022, 04:09:15 pm
content: Quote from: coppercone2 on January 12, 2022, 12:56:05 pmI think this is (was?) not uncommon for some of the advancements made for the highest-frequency amateur QSOs.

author: Paul B
author_rank: Contributor
timestamp: January 27, 2022, 12:46:13 am
content: hi can you give me any information about the multiplayer with an output at 125 GHz as i am looking for a sig gen from 120 to 140 GhzPaul

author: Paul B
author_rank: Contributor
timestamp: January 30, 2022, 09:15:58 pm
content: Hi thank you for putting a link one of Neil's videos on the threadbut I am trying to get the parts together to do RF measurement between 120 and 140 Ghzso looking for any multipliers for the above frequencies with wave guide outputfor characterising aerial parts Neal is designing and making to very high tolerancesalso looking for power meters in WR8 90 to 140 Ghz noting that i have limited budgetRegards Paul

author: Paul B
author_rank: Contributor
timestamp: February 10, 2022, 08:30:16 pm
content: Hi allcan any one suggest a suppler of a signal generator or multiplayer to cover 115 to 145 GhzRegards Paul

author: profdc9
author_rank: Frequent Contributor
timestamp: February 10, 2022, 08:35:58 pm
content: A number of years I built a "radar" based on mm-waves. But you could actually do it with thermal sources.Thermal sources are the poor man's mm-wave generator. You can still do a lot of stuff with them like interferometry, imaging through objects etc. I used a VDI generator though.Check out:https://opg.optica.org/oe/fulltext.cfm?uri=oe-22-13-16393&id=294316By the way, a way to do a "spectrum analyzer" for mm-wave is to build a FTIR.

author: Paul B
author_rank: Contributor
timestamp: February 11, 2022, 01:36:46 am
content: Thank youjust printing it out but i am baffled how you can generate rf from light and ask can i easy generate 1 MW at 110 GHzPaul

author: coppercone2
author_rank: Super Contributor
timestamp: February 11, 2022, 01:53:23 am
content: the black body radiation spectrum of something hot enough makes THz radiation.I kind of like the idea of a microwave oven heated SiC globar for THz generation, so long you filter out 2.4GHz well it might be decent? At least give you something cheap to experiment with. Probably hard to make that safe and FCC compliant though.

author: Joel_Dunsmore
author_rank: Regular Contributor
timestamp: February 11, 2022, 04:23:10 am
content: Quote from: Paul B on February 10, 2022, 08:30:16 pmFixed frequency (CW) or modulated. Check out multipliers from sources such as Virginia Diodes, OML, Eravant. You can marry it to an Microwave synthesizer. If you are needing modulated signals, then you need an upconverter plus a to signal generators. Very much what you need depends on what you are trying to do.

author: KE5FX
author_rank: Super Contributor
timestamp: February 11, 2022, 05:32:34 am
content: I was going to suggest Raytheon, if he wants 1 MW at 110 GHz.I imagine there will be a lot of end-user paperwork involved.

author: Paul B
author_rank: Contributor
timestamp: February 11, 2022, 03:30:08 pm
content: Hi Joel and ke5fxI only require a cw signal but square wave modulation would be an advantage as it can then be used with an AC scalar analyser as this is the capability i have up to 80 GHzThe problem hear is that i only have limited funded as it is a hobby so looking to do it for less than £2000 probably looking for older technology that i can afford such as a BWO or IMPATTcurrently using Gigatronics frequency extender with X2 , X3 , X4 to go from 20 to 80 GHzI am using a HP 70000 system as the analyser to 170 Ghz with a OML detectorre your line (I imagine there will be a lot of end-user paperwork involved ). strange as those within the USA have been buying Milemetric RF test equipment from USSR for over 22 years

author: coppercone2
author_rank: Super Contributor
timestamp: February 11, 2022, 03:38:53 pm
content: I don't think you will have paper work problems for low power ones, they are not weapons. A car radar is 70GHz after all and its all over the place. It probobly harmonics to 140GHz since its cheap crap you put in a caryou wroteMW notmW megawatt vs milliwatta megawatt one would be a Combine suppression field emitter in City 17 (so detectors are always nice)

author: Paul B
author_rank: Contributor
timestamp: February 11, 2022, 05:34:44 pm
content: HiRe MW compared to mw point taken a slip of the handThere are now car radar unites at 122 Ghz but i want to do experiments on horn aerials and do a sweep from 120 to 140 ghzregards Paul