Electronics > Beginners

Why are spectrum analyzers so expensive?

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codingwithethanol:
@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 100mhz
http://prntscr.com/nzpvbc
@RoGeorge yeh im gonna need a few more fundamental fridays to understand that shit

T3sl4co1l:
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

RoGeorge:

--- Quote from: codingwithethanol on June 10, 2019, 12:04:25 am ---gonna need a few more fundamental fridays to understand
--- End quote ---

The first couple of pages from here might help:  http://www.sjsu.edu/people/raymond.kwok/docs/project172/EE172_YIG_oscillator.pdf

About 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.

David Hess:

--- Quote from: codingwithethanol on June 09, 2019, 09:34:31 am ---Also, 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?
--- End quote ---

Tektronix made one like that which could be used with any oscilloscope.

http://w140.com/tekwiki/wiki/1401

ejeffrey:
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.

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