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.
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 spectrum analyzers 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 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.
Regarding your choices:
why are spectrum analyzers so expensive, best spectrum analyzers, what is spectrum analyzers, how much does a spectrum analyzer cost, why spectrum so expensive
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 spectrum analyzers 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.
Spectrum Analyzers are expensive for several reasons:
- 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.
- 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...
- 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.
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