I'm planning to buy a spectrum analyzer (Signal Hound) or may be some different like Rigol/Siglent.
I want to know if my understanding are correct, like how its going to help me. I mostly work on 433Mhz, 915Mhz and 2.4Ghz frequncy based modules, while development I'm not sure if radio was activated and it transmitted some signals, spectrum analyzer will help me to see if in that particular frequency spectrum had some activity. I believe using some USB based SA will give me some additional advantages by using the strength of PC Software to see more details and even to some point demodulation.

I wanted to know if my understandings are correct and I'm choosing a right tool.

 

What, precisely, do you want to measure?

It sounds like all you are really interested in is power in particular bands (is the module on-the-air when it should be?). If this is the case then an SA is extreme overkill. An SA can be used to check for things like spurious emissions if you are building radio transmitters or locating emissions in a band if you don’t know where they are.

But a much more flexible option for what seems to be your needs, that can do what you want and more is an SDR radio. High quality SDR radios, which can also be used to receive and decode the protocols you are using, are also much cheaper than good SAs.

As an example, on the high end (of low cost) is the HackRF One that costs ~$350USD for a complete kit including interseries connector adapters.

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This will require a computer, but combined with any of several open source software packages, it is a powerful tool for the sort of work you are doing. It can provide a waterfall display showing a section of the band (up to 20MHz in this case) and the presence and relative signal strength of transmissions. It can also be used to decode the protocols used by remote control and data communications modules.

the open source QSpectrumAnalyzer [GitHub repo]
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If you forego being able to transmit, a dirt cheap (~$30USD for a good one) option for the lower bands (not 2.4GHz) is RTL-SDR which is an open source ecosystem based on a chipset used in DTV dongles.

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You can use it with the really great, free, SDR# from AirSpy, or you can buy their much more capable (covering up to 1.8GHz with much better specs), and much more expensive (3x at ~$99USD).

Anyway, you get the idea. This is something you should do research on and make choices based on your interests and needs, but I am convinced you would find that for your needs an SDR radio would have far more utility for far less money than an SA.

 

Thanks for detailed answer, by chance I came across HackRF One and bought one from AliExpress that I received yesterday. Now I'm trying to install QSpectrum Analyzer and SoapSDR on Ubuntu, can you please share any resources that you think could be helpful to setup SDR on ubuntu, as I'm having issue. I'm following instruction at https://github.com/xmikos/qspectrumanalyzer

I'm a windows person I tried it first on windows but I came to know that QSpectrum Analyzer has some issues running on Win.