Why are spectrum analyzers so expensive? - Page 1
Forum section: electronics / beginners

author: codingwithethanol
author_rank: Regular Contributor
timestamp: June 09, 2019, 09:22:11 am
content: I've recently been making myself a mini lab so I can move past arduino and do some actual engineering. I wanted to get a spectrum analyzer to view frequency response of components, but I looked at the prices of the cheapest analyzers and had a stroke. What makes these things so expensive, are they made out of platinum and diamonds? Not saying that I don't understand why the super serious business pro models are expensive, but where are the budget hobby tier models?

author: bd139
author_rank: Super Contributor
timestamp: June 09, 2019, 09:28:35 am
content: Because they’re very complicated, the bits cost a lot of money and the engineering effort to design one is pretty extensive.Not joking but they are pretty cheap now really. Just the SA plug in for my tek scope I had recently (7L12) with inflation would cost $25000 today. Add another $20000 for the scope mainframe and a couple of basic plugins for it so you get a scope too. So $45k down.That Rigol or Siglent looks like a bargain now.Or you can buy the 25 year old $45k one which is vastly inferior for $200 and fix it which is what I did.

author: codingwithethanol
author_rank: Regular Contributor
timestamp: June 09, 2019, 09:34:31 am
content: WOWAlso, speaking of plugins, I don't have a 7000 series tek to plug that into, but i was also wondering why there isn't just a black box with some BNC ports you can connect to your oscilloscope to have SA functionality on a budget?

author: codingwithethanol
author_rank: Regular Contributor
timestamp: June 09, 2019, 09:56:09 am
content: http://prntscr.com/nzhwh4HRNNNNNNGWhen I say budget im talking $100-$200. I've checked a few DIY SA projects but they are all far beyond my expertise to build

author: bd139
author_rank: Super Contributor
timestamp: June 09, 2019, 10:04:07 am
content: Quote from: codingwithethanol on June 09, 2019, 09:34:31 amYes Thurlby TSA250 and TSA1000 spectrum analysers. they are pretty crap though. They come in under your budget.It's possible to get a good deal but you have to lurk and there's a risk element.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: June 09, 2019, 10:15:46 am
content: There are handhelds, and RTL-SDR, and so on. Haven't spotted any yet?The good old ones are either well sought after (e.g., classic HP 8590 and such), high spec and quite practical (pretty much anything newer: faster sweep, PLL locked or DDS, FFT...), or both. $1000 is a good starting point for a proper benchtop instrument that you want to do real work with. (Coincidentally, the DSA700 is around $700, not a bad deal considering.)As for why -- keep in mind, second hand market prices fluctuate with demand, so they aren't necessarily representative of the effort needed to build one of these.The old ones are made from radio parts, exactly as given: a high frequency oscillator into a mixer, IF1 filter, another oscillator and mixer down to an easier-to-manage IF2, then detector and plotting.- There's no preamp, or not usually; that would impair dynamic range. Mixer also adds ~6dB mixer loss, but specs aren't usually optimized for noise figure.- IF1 is quite high, above the input bandwidth -- to avoid images. It's filtered to avoid images on the next stage. It's converted down to IF2 where things are easier to handle.- IF2 (or maybe there's an IF3, easier to manage images/filtering this way) is where most of the actual filtering is done (i.e., receiver bandwidth RBW). These are usually separate, carefully tuned filter chains, selected by relay or whatever.- Detector is linear or log, and peak or average reading. Or something inbetween, like the quasi-peak used for EMC work. More selectable signal paths.- Final output might be plotting sweep and detector output on a screen, or a sampler, and plotting that on a digital readout, or transmitting via data port.There may also be selectable IF stages, when wide input ranges are needed. When you see teardowns of newer specs, with all those shiny planar filter circuits, you're most likely seeing some of this at play.There's also the DSA (Digital Signal Analyzer), basically an ADC married to an FFT. Classic ones like HP 3562A only do ~100kHz, but modern ones (like Rigol's DSA700) do RF in real time (what a difference a half dozen orders of magnitude in computation power can do, right?).Which, on that note -- a DSO with FFT functionality isn't much different. It won't have the spectrum-related features that a DSA does, but if all you want is to see some peaks, it's a good deal.A DSA is basically a DSO with FFT on top, whereas a DSO is a DSA with waveform capture (triggering) on top. Not too too different, but different enough to be separate products.Tim

author: codingwithethanol
author_rank: Regular Contributor
timestamp: June 09, 2019, 10:19:17 am
content: Awesome recommendation but there arent any listings on ebay, so im gonna stay posted and wait for someone to put one up for sale. I had googled it and found 2 older listings that had gone for 60 and 250, so im hopeful

author: exe
author_rank: Unknown
timestamp: June 09, 2019, 10:23:19 am
content: Another "cheap" option:https://www.sdr-kits.net/I myself going to tryhttps://www.sdrplay.com/rsp2pro/... eventually.

author: bd139
author_rank: Super Contributor
timestamp: June 09, 2019, 10:26:03 am
content: Quote from: T3sl4co1l on June 09, 2019, 10:15:46 amYeah they're not too terrible at that actually. Not a bad solution.Here's one I did with a receiver I was building recently. Pre IF filter mixer products, on DS1054Z:After crystal IF filter.Obviously not great for measurements or particularly high frequencies but it does help design considerably.I will buy a DSA815TG at some point however. Next time I need more than HF band SA.

author: Psi
author_rank: Super Contributor
timestamp: June 09, 2019, 10:27:37 am
content: Is there anything like theHackRF Onebut in a spectrum analyzer style box with a LCD/touchscreen ?I'd love to get a basic spectrum analyzer with up to 6ghz for under $1k.I'm not messing around with something that needs a PC, it has to be portable, ready-to-go in a box.I think there is a market for something cheap that can get the 5.8ghz band covered.A lot of people don't really need the advanced spectrum analyzers functions that you go without in a SDR style solution.Since the hackRF One is $299 it should be totally doable to have something in a box with a screen for under 1k

author: codingwithethanol
author_rank: Regular Contributor
timestamp: June 09, 2019, 10:44:28 am
content: @bd139 I have a budget tek right now but i was thinking about getting a little rigol down the line so thats good to know@blueskull appreciate the input but those are still wallet biters@T3sl4co1l yeah ive seen those but theyre mostly useful for hams, im trying to measure frequency response of filters and other circuits

author: codingwithethanol
author_rank: Regular Contributor
timestamp: June 09, 2019, 10:47:50 am
content: @exe that looks interesting but im wary of all PC based equip due to trash software support@Psi does that have any affiliation with the GS youtube channel? Interesting coincidence if not

author: Bicurico
author_rank: Super Contributor
timestamp: June 09, 2019, 10:48:29 am
content: Spectrum Analyzers are expensive for several reasons:1) There is not a big market for them, so all engineering, research and development costs are split up between a fairly small amount of customers. This has changed recently with companies like Rigol and Siglent, mass-producing them, which lead to incredible affordable prices.2) Spectrum Analyzers use expensive components. The core component of older swept spectrum analyzers (SSA) is the YIG, which is contains small Yttrium spheres for frequency down-mixing. If you search this forum, you will find posts from people trying to repair them and it is amazing technology - almost black magic! I still wonder how this can possible work at all. Then, modern spectrum analyzers offer FFT modes (Fast Fourrier Transformation). Instead of sweeping the frequency range, they digitize millions of samples and convert these time-domain samples into frequency domain. This requires a lot of processing power! It also allows a super smooth spectrum and waterfall display. Look at the 6-figure price tag Rohde&Schwarz spectrum analyzers and you get an idea...3) High Frequency stops being "reasonable" at around 1GHz. Once you get above that value and especially above 2GHz, things start to behave oddly and you really need to take care of every detail: connectors, cables, everything needs to be "special" to not interfer with the signal you are analyzing. This becomes extremely expensive!Regarding your choices:50-200 Euro: You can purchase chinese clones of the NWT series. These work surprisingly well and I developed an alternative software for these devices. Take a look at my blog about this:https://vma-satellite.blogspot.com/500-2000 Euro: You can consider second hand spectrum analyzers. These were normally very expensive machines, which are now sold at ridiculously low prices. But beware that you get no support, calibration and often no spare parts. What I have done is buy several broken units and then repair them, using some for spare parts. This way I ended up with 2x R&S CRTU, 2x R&S CMU200 and 1x HP 8594E. All in working order. But I have another 2x HP8594E (broken PSU) and 1x R&S CRTU (missing some boards) and spare parts. This takes space, time and money to get them in working order. And you still have no valid calibration, if that is important for you.1500 Euro: Get yourself the best performance/price ration currently on the market and buy a Siglent SSA3021X. New, calibrated with warranty. And it can be hacked for increased bandwith (3.2GHz) and all options.Regards,Vitor

author: Bicurico
author_rank: Super Contributor
timestamp: June 09, 2019, 10:57:49 am
content: Forgot to add some thoughts on SDR:Yes, you can buy a HackRF One and run this amazing software:https://github.com/pavsa/hackrf-spectrum-analyzer. But you will soon find out that functionality/measurements are limited and that the software/device crashes a lot.Then you have the ADALM Pluto: I cannot recommend this as a spectrum analyzer replacement, at all.SDR: Yes, with SDR# (sdrsharp) you can do spectrum analysis and even demodulate most analog and some digital signals! BUT: In my opinion this is in no way a replacement for a real spectrum analyzer. These devices do not support a swept spectrum analysis, so that your frequency range is limited (4MHz to 40MHz, depending on the signal). If you want to look i.e. at the CATV band from 50-850MHz, you won't be able to do that, unless you buy the SDR# specific AirSpy, which costs a lot more than a regular RTL2832 dongle.Plus, most tools are Linux only and you can literally spend hours to get a particular driver/software up and running. GNU Radio is great and you can learn so much using it - especially if you are interested in HF engineering and have a Python/C++ programming background. Sounds complicated? It is!In my honest and modest opinion, if all you want is a spectrum analyzer, then either go cheap with SMA/NWT devices or buy a SSA3021X or spend some time reading about which are the best second hand devices to buy. I think there was a whole thread here about second hand spectrum analyzers.Good models are HP/Agilent 859x series (beware of the PSUs - they are a nightmare to repair: I have 3 broken ones and repair seems impossible) and Rohde&Schwarz CMU200/CRTU - these are actually Protocol/Communication Tester, but offer a fully working spectrum analyzer, too.Regards,Vitor

author: codingwithethanol
author_rank: Regular Contributor
timestamp: June 09, 2019, 10:58:53 am
content: Why is Yttrium required?I had a hunch these things ran on fairy dust but HUH?

author: codingwithethanol
author_rank: Regular Contributor
timestamp: June 09, 2019, 11:08:05 am
content: Anyways the reason I started this thread is because im working on student budget here. I had gotten a decent tek and psu and function generator for <$200 and couldnt justify shelling out more than that for ONE piece of equipment. Im taking all the suggestions made into consideration, also I found this thing:https://www.ebay.com/itm/U-V-UHF-VHF-Dual-Band-Spectrum-Analyzer-w-Tracking-Source-136-173MHz-400-470MHz/292520566371?hash=item441b959e63:g:gBoAAOSwQFVapi2aBut it looks like it'd shit itself and blow up if I so much as looked at it wrong. Also I found a Hameg SA at auction just now but it was a little over the $200 mark so I didn't pull the trigger.

author: HB9EVI
author_rank: Frequent Contributor
timestamp: June 09, 2019, 11:28:52 am
content: Most things were already pointed out. I think, analyzers nowadays are quite affordable;first it was the Rigol DSA815TG, today it's the Siglent with better technical data than the Rigol for entry class.After having twice time tough luck with 2 older storage Tek scopes breaking down irrepairably, I decided to not buy anymore old measurement devices, so I went for the Rigol which does an ok job here; if you know about its limits you can fairly work with it and I'm using it rather often - it's certainly much better than all those FFT functions modern DSOs offer, what can imo not be seen as 'measurement'.If you personally see a need for a SA, new or second/third hand go for one with a tracking generator; it's a must-have for many measurements

author: Bicurico
author_rank: Super Contributor
timestamp: June 09, 2019, 11:56:46 am
content: I would not recommed wasting money in this device.For your budget you can only buy a SMT/NWT device, which requires a PC.All options with a display is money thrown away.RegardsVitor

author: Theboel
author_rank: Frequent Contributor
timestamp: June 09, 2019, 12:14:53 pm
content: I think You don't give information about how high You want to go 100MHz, 2GHz ?based from Your post :"I've recently been making myself a mini lab so I can move past arduino and do some actual engineering. I wanted to get a spectrum analyzer to view frequency response of components, but I looked at the prices of the cheapest analyzers and had a stroke. What makes these things so expensive, are they made out of platinum and diamonds? Not saying that I don't understand why the super serious business pro models are expensive, but where are the budget hobby tier models?"You can try to use Arduino for made Your own spectrum analyzer, something like this perhaps

author: Mechatrommer
author_rank: Super Contributor
timestamp: June 09, 2019, 03:07:05 pm
content: Quote from: bd139 on June 09, 2019, 10:26:03 amwith PC aided SW, one can do much more... GSps and vertical bit resolution are the only limitation.

author: bd139
author_rank: Super Contributor
timestamp: June 09, 2019, 03:14:13 pm
content: Might have a play with that. The software FFT on the Ds1054Z is a bit poo for some things to the point for low frequencies I use a sound card and Spectogram for it instead.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: June 09, 2019, 03:50:07 pm
content: Quote from: codingwithethanol on June 09, 2019, 10:58:53 am"Physics. It works, bitches."That was an incomplete description, but yttrium is indeed involved -- the module is a YTO (YIG Tuned Oscillator). The active ingredient is a YIG (yttrium iron garnet) sphere. YIG is a ferrite (i.e., a compound of some metal oxide with Fe2O3, or to put it another way, iron(III) ferrate), specifically one taking the garnet crystal structure. (Whereas most ferrites are in the spinel group*.)*Chemistry aside:The mineral spinel has the formula MgO.Al2O3, but the Al can be substituted with Fe giving a ferrite, and the Mg with a variety of metals (Fe, Mn, Zn, Ni, etc.), making this a huge family of continuous mixtures of similar atoms. Soft ferrites are (Mn,Zn) and (Ni,Zn) ferrite. The mineral magnetite is actually iron ferrite, FeO.Fe2O3!In terms of electrical properties, YIG has lower saturation flux density (because there's less active magnetic iron, and more diluting or opposing atoms), lower relative permeability, higher resistivity, lower losses, and notable paramagnetism.It's the last property we're interested in. When subject to a static magnetic field, unpaired electrons (the part responsible for bulk magnetism in the first place) precess at a frequency proportional to that field. (The physics is similar to the precession of a spinning top, where the precession rate depends on the force trying to tip it over, i.e., gravity in that case, ambient magnetic field in this case.) The precession in turn manifests as electromagnetic energy (photons; this is a quantum process too, after all), which is to say, light waves. Or at typical field strengths, radio waves more specifically.So the really interesting property is this: when an inductive loop is coupled to a YIG crystal, and the crystal is placed in a magnetic field, there is a blip in the frequency response of that loop, which varies with magnetic field intensity. The blip looks much like the impedance response of a quartz crystal, having a series and a parallel resonance, and you can tune in either one. Or, as far as I know, it's usually done with two perpendicular inductive loops, so that they are only coupled through the YIG crystal's resonance (getting a bandpass characteristic), and serve as the input and output terminals of a microwave-frequency resonator. Add an amplifier and buffer, and you've got a YTO module!The tunable range doesn't go all the way to zero, of course; that would be kind of horrible to design (those inductive loops won't work very well at DC!). Usually it's, like, say, 3-6GHz or such. Which is perfectly fine because as mentioned before, LO1 will be somewhere at high frequencyA few other practical considerations include magnetic design (the module housing is usually steel, cut in a "pot core" sort of shape to give good shielding to external fields, and better field intensity (and uniformity) around the crystal itself), thermal design (the electromagnets are normally wired differentially, so as to maintain the same total heat dissipation while varying the total field), and so on.So, because the YTO is tuned by magnetic field, it can be tuned electronically. Fantastic, huh?Tim

author: ebastler
author_rank: Super Contributor
timestamp: June 09, 2019, 04:14:37 pm
content: Quote from: Theboel on June 09, 2019, 12:14:53 pmYep, without any information about the required frequency range, this discussion and any recomendations are flapping in the breeze.@codingwithethanol: What signals do you want to look at?In the audio range, a decent sound card and free FFT software are a good bet. You can even get a combined sweep generator and Bode plotter for your sound card.In the 100 MHz range (order of magnitude), the FFT function on entry-level DSOs may do what you need -- or, again, the Bode plot function some scopes offer.If you want to look at GHz frequencies, things get expensive...

author: RoGeorge
author_rank: Super Contributor
timestamp: June 09, 2019, 05:01:33 pm
content: Quote from: codingwithethanol on June 09, 2019, 10:58:53 amIf you want to know more, take a look inside a YIG oscillator (starting from minute 33:28):

author: Bicurico
author_rank: Super Contributor
timestamp: June 09, 2019, 05:30:36 pm
content: Thanks T3sl4co1l and RoGeorge:YIG/YTO are magic, no matter how great the explanation on how they work!Regards,Vitor

author: codingwithethanol
author_rank: Regular Contributor
timestamp: June 10, 2019, 12:04:25 am
content: @T3sl4co1l So yttrium is used to create a magnet controlled bandpass?@ebastler mostly low freq stuff like audio filters but I did want to experiment with AM/FM so yeah up to around 100mhzhttp://prntscr.com/nzpvbc@RoGeorge yeh im gonna need a few more fundamental fridays to understand that shit

author: T3sl4co1l
author_rank: Super Contributor
timestamp: June 10, 2019, 01:47:38 am
content: I think the role of yttrium specifically is either, it opposes the magnetic field less than other options, or it doesn't interact and just acts as a dilutant; and in either case, it happens to be the right size atom to make a garnet crystal, when combined with iron. And the garnet is important because of where in the crystal the iron atoms sit, which determines how they interact and therefore the magnetism.In any case the important part is not yttrium, it's that it's a garnet made with iron, and yttrium happens to be necessary to make that happen. And then that the result is magnetically tuned, yes.Tim

author: RoGeorge
author_rank: Super Contributor
timestamp: June 10, 2019, 02:31:35 am
content: Quote from: codingwithethanol on June 10, 2019, 12:04:25 amThe first couple of pages from here might help:http://www.sjsu.edu/people/raymond.kwok/docs/project172/EE172_YIG_oscillator.pdfAbout the spectrum analyzer, for audio range it wont help you much. Many of those very expensive SA doesn't even cover such low frequencies. They are mostly for the RF, where MHz or GHz range is needed. kHz range might be useful for switching power supply noises and such, but not much for audio. There are dedicated SA for the audio range, thought.For frequency up to 100MHz, you can sometimes get away without a proper SA by improvising with just an oscilloscope and a sweeping generator, depending on what you want to measure.For audio only, a sound card and a FFT program will be enough in most cases. In fact, a good sound card would be hard to beat even by those very expensive specialized audio spectrum analyzers. IMO for learning purposes, a sound card is more than enough.

author: David Hess
author_rank: Super Contributor
timestamp: June 10, 2019, 03:01:06 am
content: Quote from: codingwithethanol on June 09, 2019, 09:34:31 amTektronix made one like that which could be used with any oscilloscope.http://w140.com/tekwiki/wiki/1401

author: ejeffrey
author_rank: Super Contributor
timestamp: June 10, 2019, 04:05:26 am
content: As for why YIG spheres are used: it basically boils down to "inductors are garbage". The phase noise of an oscillator is controlled by the Q factor of the resonance you use to set the frequency. Same with the out of band rejection of a filter. Resonators can be made from ordinary inductors and capacitors. Capacitors are not too bad: vacuum or low k dielectrics are nearly lossless. But inductors tend to be quite lossy at high frequency unless you make them out of superconductors which isn't usually convenient.The normal solution is to use quartz crystals. The Q of their electro-mechanical modes are incredibly high which is why they make such great oscillators and filters.The one problem with quartz crystal filters is that you can't easily tune them. You can slightly pull the frequency with an external capacitor, but you can't easily change the motional LC circuit parameters.YIG spheres are basically the solution to that problem: a high-Q resonance that is broad-band electronically tunable.

author: hagster
author_rank: Frequent Contributor
timestamp: June 10, 2019, 05:09:15 am
content: The Airspy mini is an om option as an SDR based spectrum analyser. SDR# comes with an SA application that sweeps pretty quick and has good dynamic range and low noise floor. Much better than the hackRF within the frequency limitation of the Airspy. Only 70USD.https://airspy.com/airspy-miniIts not really the same as a proper SpecAn and you won't really be able to make any kind of calibrated measurements with it though.

author: chrisc
author_rank: Unknown
timestamp: June 10, 2019, 05:26:19 am
content: Quote from: bd139 on June 09, 2019, 10:26:03 amOn that topic, ElectroBOOM gives an example of using FFT in a scope while debunking yet another “free energy” claim:(Skip to 3:40; it looks like the auto-embedding strips the time offset).

author: T3sl4co1l
author_rank: Super Contributor
timestamp: June 10, 2019, 06:14:01 am
content: Quote from: ejeffrey on June 10, 2019, 04:05:26 amOne final touch to this -- you can still make a very nice LC oscillator (if still maybe not as low noise as you'd like, for the above reasons), that's voltage controlled using varactors, but it won't be very linear. The neat thing about YIG tuning is, it's proportional to magnetizationbecause physics-- so the VCO linearity is very good indeed, and little compensation or calibration is needed!On a related note, I wonder if anyone ever tried making, say, a tunable quartz or mechanical filter, that uses a stretchy or bendy substrate as resonator, so that the dominant mode can be varied over a modest range.In a completely different direction, there are cavity resonators with free electrons -- that's right, vacuum tubes, specifically, reflex klystrons. Apparently these are quite low noise, and are electrically variable over a modest range. The internal function is something like: an electron beam shoots towards a negatively charged reflector electrode, inside a resonator cavity. The field inside the resonator controls electron motion, transforming electron energy into resonant energy. The reflector electrode controls how soon this happens, tweaking the frequency within the bandpass range of the resonator. IIRC, a typical range is maybe 100MHz out of a 5GHz center frequency -- good in its day (a reminder that the widest bandwidth all- tube system was probably the Tektronix 585, topping out at 100MHz baseband). Downsides include, well, all the vacuum tube stuff you need (heater power, high voltages), FM-to-AM conversion, and relatively low power output.Tim

author: bd139
author_rank: Super Contributor
timestamp: June 10, 2019, 07:05:08 am
content: I’m using the aforementioned LC + varactor oscillator as the first LO on my toy spectrum analyser. This uses an SA612 as the first mixer and VCO. I can get 180-305MHz out of that. As for linearity, yep it’s awful. I’m playing with a linearisation network using diode clamps on the sweep input. This is as far as I have got though.

author: lordvader88
author_rank: Frequent Contributor
timestamp: June 10, 2019, 07:07:25 am
content: I for 1 can't wait to make a 1970/80s era kit style SA. They look so cool with all the copper clad shielding and parts.

author: bd139
author_rank: Super Contributor
timestamp: June 10, 2019, 07:12:48 am
content: http://hfsignals.blogspot.com/p/specan-reboot-of-w7zoi.html?m=1

author: JohnPen
author_rank: Regular Contributor
timestamp: June 10, 2019, 07:54:51 am
content: For those of an adventurist nature you could build a Scotties Spectrum analyser. However it is not that cheap, because of component costs, and takes quite a while to build. Also sourcing suitable VCO chips has become more complicated as Minicircuit's no longer make the VCO chips. It is still cheaper than purchasing a Rigol or Siglent and you learn a lot but it is a somewhat long term construction project.However reading through Scottie's site provides a lot of useful information on understanding and building your own Spectrum analyser. There is also a dedicated Yahoo group, see below, which provides great support for those who bite the bullet.http://scottyspectrumanalyzer.us/https://groups.yahoo.com/neo/groups/spectrumanalyzer/conversations/messages

author: RoGeorge
author_rank: Super Contributor
timestamp: June 10, 2019, 08:28:49 am
content: Quote from: T3sl4co1l on June 10, 2019, 06:14:01 amThat was exactly my thought, too. To experiment with a decapped Quartz by pressing it in a vice with rubber jaws, and see how much the resonant frequency can be shifted without snapping the crystal. If it would be enough, the next step would be to replace the vice with some piezo material in order to electrically control the mechanical pressure, and thus the resonant frequency.Most probably this idea was already tested before, and the results were nothing spectacular, so we don't have today such a device commercially available, but still, it will be an interesting experiment to tinker with.

author: ebastler
author_rank: Super Contributor
timestamp: June 10, 2019, 09:19:44 am
content: Quote from: RoGeorge on June 10, 2019, 08:28:49 amMy gut feeling is that this would provide a small tuning range and bad frequency stabilty (since the inherent stability of the quartz crystal is compromised by external, macroscopic mechanisms which will be affected by temeperature drift, vibration etc.). The worst of both worlds.

author: IDEngineer
author_rank: Super Contributor
timestamp: June 10, 2019, 05:37:01 pm
content: Quote from: T3sl4co1l on June 10, 2019, 01:47:38 amI've studied YIG's for quite a while as a sort of side interest. Like the other respondent(s), it still feels like the stuff of science-fiction. Kinda like "red matter" in Star Trek or that beryllium time-travel device in Galaxy Quest. "Captain, we can't increase the field through the YIG sphere! We're already past the redline! Nobody's ever even tried to go this far before!"IIRC, the magnetically tunable behavior is believed to result from theasymmetriclocation of two of the Fe atoms in the crystalline matrix. It took me a while to learn that. For a long time I thought it was due to the yttrium content, because in many applications yttrium behaves a lot like a rare earth - which have consistent outer shells and differ by how their 4f shells are filled, giving rise to their similar chemical behavior yet differing magnetic behavior. However, in the case of YIG, your comments appear spot-on... what's needed is a crystalline matrix that asymmetrically positions the Fe atoms and Y+I does that.The one thing I haven't been able to discover is who the heck originally figured this out - or even conceived of the concept that properly, asymmetrically positioned Fe atoms would yield magnetically tunable resonance in a physical object, with linear response to boot. That's a person or team I'd like to know more about. What the heckelsedid they do that doesn't get enough publicity?

author: ejeffrey
author_rank: Super Contributor
timestamp: June 10, 2019, 06:18:53 pm
content: I haven't looked at the behavior specifically of YIG spheres, but in other non-linear optics (like an EOM) the normal requirement is that you need a crystal that does not have inversion symmetry in order to get a second order non-linearity. In that case your output field is proportional to (input field x control field) (aka a bilinear response -- linear in two different fields). This has a straightforward analogy in non-linear circuits: if you have an analog circuit with symmetric clipping diodes you get only third order non-linearity (and higher odd orders). You need an asymmetric circuit to get even order distortion.If you have an inversion symmetric crystal you only get 3rd order non-linearity which usually means adjustment is quadratic in the applied field, which tends to require much larger tuning fields.