RF Spectrum analyzer realization - Need your help

Hi all,

I’m involved in a RF project but I haven’t enough experience in the field to understand the right way to take, so I’m asking your help. Thanks to all in advance for it.

The project is related to the design and realization of an amateur RF spectrum analyzer capable to detect frequencies in range 300MHz – 2.5GHz, in order to evaluate if a mobile phone, a WI-FI, a micro-spy device is transmitting in a range of few meters (approx. 3-5 m).

The precision needed is not high, I mean for example it’s not important to understand if there is a transmission at 900 MHz or 920MHz or the exact amplitude at this frequency. What is important is to be able to say there is a transmission at about 900MHz and the amplitude is relevant, and so there is a hidden communication somewhere in a few meter range.

I’m starting from this scheme:
https://oscilloscope-tutorials.com/Spectrum_Spectrum_Analyzer_Fundamentals.aspx

Some blocks are easy to understand for me, others no (for example: first two blocks on the left: RF attenuator and Preselector; and again block after RF gain), so if someone can give me any detail it’s appreciated.

Anyway, how would you approach the problem?

A good way to produce a basic Spec An is to build it around a TV Tuner.

Electronics Australia magazine (now gone ) did a project in the early
1990's that used a standard tuner that covered the VHF low and hi bands and
the UHF band and the project was connected to an oscilloscope for display
it worked very well and was my first spec an.
Now for the freq range you are interested in you could possibly use a tuner
designed for a satellite box they cover ~ 900 - 2200MHz give or take a
few MHz you ahve a sweeping voltage that is linked to the tuning voltage pin
on the tuner to be able to tune across the range of the tuner. That sweeping voltage is also sync'ed to the external "X trigger" input of the oscilloscope.

thats a start for you give you some ideas

Dave
VK2TDN

Another way could be the use fo a modern integrated receiver with RSSI capibilities such as TI CC1101 (sub-1 GHz) or CC2500 (2.4 GHz).
The idea is based on the capability of measure the received signal amplitude inside the IC bandwidth (usually you can trim it, so you will have a RBW parameter).
TI has developed a project (with a student, I think) available in their web site.
To enlarge the available bandwidth my idea is to build a kind of superhet receiver using a wide tuning synth and a downconverter (and a SAW optional), like the one used in basestation, in front of the receiver.

Mazz

here are some links for spectrum analyzer examples.

https://hem.passagen.se/communication/tuner.html
https://www.qsl.net/va3iul/SA/spectrum_an.html

Hi Ninochip,
I would not select "the way of TV-tuners application", they has some "holes in the band, but if these part of frequency is not of your interest...

Some good lectures:

I belief, that one of the best "Home Browed" SA`s is from Borber to find:


Or even from; GBPPR 0 - 1000 MHz Spectrum Analyzer, **broken link removed**
Tracking generator by KE5FX.T ek TR503 Compatible_www.qsl.net/ke5fx/tr503.html
In all case you can find more good designed form European + American Radio amateurs too...
Pls. read some scripts on web, Qsl.net, UHF-communications etca..

Good luck!
K.

Hi.
i have worked on the project of spectrum analyzer upto 6 ghz.
the first thing you have to do is the architecture selection.
How many IF stages you want as per the super heterodyne architecutre, I guess two IF stage architecture is good choice for analog implemented rbw and 1 if stage for digitally implemented baseband.
After that frequency planning stage of all the modules comes in picture.
The frequency of 1st IF you have to select such that the 1st IF is out of band of frequency band of spectrum analyzer.
Design the baseband as per the requirement.
I think you have to freeze the specifications completely before going to the implementation stage.
Hope this helps.
Regards,
ankit

Nowadays, I would be tempted to find a monolithic sampler circuit, with built in pulse generator, to be the front end. You could drive the pulse generator with a tunable VHF/UHF VCO.