I am working with Arduino boards and some radio modules (all in ISM bands, i.e., 315MHz, 433MHz, 868MHz, 915MHz, and 2.4GHz) that do not have any circuits to give the RSSI of a received message. I need to keep a log of this information for a long research project (at least a few months, I am already storing the readings of other sensors, so it will be just another input).
I looked into quite a few sources, but, unfortunately, my RF knowledge is limited to how to use it, not how to measure it or to understand its characteristics deeply...
The most promising thing/part/circuit/module/gadget that I found is the AD8318, but it seems that the wide bandwidth (100MHz to 8GHz) may be a problem because I will not be sure if I am reading the correct RSSI or interference of another source. When I was studying band-pass filters again to solve this issue, I realized that I would probably lose time and money and would not achieve anything useful.
My question is:
1- Is there a way to use an "external" RSSI circuit/module/part to get this value of a received message (just of a received message, not from other sources) of a given ISM radio module? Please recall that I have to store this value with my Arduino boards, so I cannot use a high-tech spectrum analyzer.
2- I know that each band has a specific antenna (length), but when I watched this video (Build A RF Field Strength Meter - YouTube), the AD8318 seems like to get all bands anyway.
Any help or tip will be welcomed!
P.S. I have a little hope that it is a simple thing that is just out of my small RF knowledge...
Not something an Arduino can do. Look for an SDR dongle that can cover the frequencies your are concerned with. You will likely need to write some programs for you PC.
SDR means Software Defined Radio. It uses your PC sound card and connects to the PC USB port.
I found a "solution" (at least, I think it is...) here in our forum: Cheap UHF spectrum analyzer (and RC tx rx) using RFM22 module - Exhibition / Gallery - Arduino Forum
In a nutshell, the guy uses a RFM22 module, which can be programmed to use different frequencies.
As I said, RF is not really my field, but I know that different frequencies need different hardware (oscillators, filters etc.), but it seem that the guy can read different frequencies.
Do you think that the best solution is buying modules that already have RSSI output?
I found a "solution" (at least, I think it is...) here in our forum: Cheap UHF spectrum analyzer (and RC tx rx) using RFM22 module - Exhibition / Gallery - Arduino Forum
In a nutshell, the guy uses a RFM22 module, which can be programmed to use different frequencies.
As I said, RF is not really my field, but I know that different frequencies need different hardware (oscillators, filters etc.), but it seem that the guy can read different frequencies.
Do you think that the best solution is buying modules that already have RSSI output?
I did look at your link. It nowhere covers the frequency range you suggest. Moreover, the guy never made an attempt to discover if the "signals" he was seeing were birdies from his own equipment or were actually from his antenna, whatever he was using.
The device can get at least the sub-GHz frequencies, which is very good for me, because all our 2.4GHz modules have RSSI outputs.
I looked at SDR devices, and I found some solutions with Raspberry Pi. Maybe it will be the "answer".
The problem in using PCs is that our nodes are in rural and outdoor areas, and these places have no structure to support a PC.
Thanks again for your suggestion! I know that it is a Arduino forum, but if you can answer one more question, it will be very helpful.
I am reading the manuals of some modules, but there is a point that is not very clear to me:
can they scan all frequencies at all times, or we have to select a narrower band?
e.g.: If a module has an input range from 1MHz to 1.7GHz, can it scan the whole bandwidth at all times or it can scan just x MHz at each time?
No, dude, I never thought that you were reading the same things that I am.
I asked that, if you know, if SDRs can scan the whole band or just a narrow band at each time.
If you don't know or don't want to answer, OK.
What you wrote was this: "I am reading the manuals of some modules, but there is a point that is not very clear to me:
can they scan all frequencies at all times, or we have to select a narrower band?".
Now how can anyone tell what "modules" you are referring to?
Please don't get me wrong. I am not trying to be rude here.
I will put in other words: Oscilloscopes are designed to analyze different inputs, just a couple at a time;TV sets are designed for watching thousands of channels, each at a time; radio sets are designed to tune thousands of frequencies, each one at a time. Are SDRs designed to scan all its range at all times, or are they designed to scan/tune just a specific frequency at a time?
SDRs do not scan! They digitize nearly the entire range of frequencies they cover. It is up to the PC software to decide on the specific frequency and mode it wants to look at. Can the PC software scan? I don't know, but would be something for you to investigate.
I have only worked with the very first iteration of using the SDR dongle back, perhaps 6 years ago. There have been many advances in frequency coverage and software facility. Basically the SDR is controlled using a graphical interface.
