Multiple Simultaneous RX chips

[gazh]

Hi guys, I'm new here so please don't bite ;-)

I've searched the forum but can't really find an answer to this.

I'm looking for a chip that will show signal strength (RSSI I guess) for a modulated FM video signal. Along the lines of RTC6715.

The problem is, I want to simultaneously monitor multiple frequencies i.e. ALL common frequencies that are used for video transmission (433MHz, 900MHz, 1.2GHz, 1.3GHz, 2.3GHz, 2.4GHz, 5.8GHz). The main idea is to detect (demodulating is not necessary) video signals. Though it is important that it does not detect, for example, microwave ovens, wifi routers, etc, I'm hoping that RSSI will help with that. I suppose that is a separate question for another day though.

I'm not expecting to find a chip that covers multiple bands, but hopefully there's something that can cover a whole band at once (e.g. 5645-5945MHz), or a significant part of it. I really don't want to have to use 50 different chips to achieve my goal.

Any advice is much appreciated!

 

[BigBoss]

To my understanding, there are multiple carriers in an environment with different modulation scheme,and you would detect FM signal modulated by a video signal.
Right ?? But RSSI circuits will detect all kind of modulations because they can not discriminate modulation schemes.
You may-perhaps-design a FM discriminator with LO+Mixer combination ( if the other sources are using digital modulation schemes) then check the modulation signal level.
But the other sources will be intereferer to your carrier and they will also be passed somehow through your discriminator.
If I'm not right, correct me..

 

[jiripolivka]

I do not think there is any simple RSSI solution to your problem.
First you must know the complete spectrum of signals, and then detect RF power of each separate signal spectrum.
For such task I would use a spectrum analyzer to start with. Then you should design filters for each separate signal spectrum section, and after such filter you can connect either a RF power meter, or a detector the output voltage of which will be proportional to the average power of a specific signal spectrum.

 

[biff44]

hmmmmmm

you could use ONE log amplifier chip, such as an AD8317. In front of the log amp, you could have a set of chip antennas (tuned to the center of each frequency band) and followed by a narrowband bandpass filter, thn into a broadband power combiner to feed the log amp detector.

As far as ignoring other types of communications good luck! If you are talking about an ANALOG video transmission, I suppose one differentiator would be that the video signal is constant...i.e. it is always transmitting with the FM modulation, whereas other types of communications send out packets and would more likely turn on and off quickly. You might simply detect if it is CW transmission or packet transmission from the log amp detected envelope.

Other than that...you are going to have to demodulate each carrier and sense if it was FM or not. MOST com systems are digital modulation, not analog, so after demodulation you might be able to tell that quickly.

 

[chuckey]

The problem as I see it is in two parts, the first is a swept frequency front end, the other, a way of detecting whether a carrier is a video FM carrier. So you tune into a signal, if its a video FM, you stop and measure its amplitude, if not you step on in frequency. The only way you can tell if the FM has video is the energy at the line frequency and at the field frequency ( or even the colour subcarrier burst frequency). So another problem is, is this piece of kit going to be multistandard?
Frank

 

[gazh]

Thanks guys! I've been looking at another way to accomplish my goal:

Use a FM receiver chip (e.g. RTC6711) and use say an ATMEGA168 to both receive the RSSI value of a given frequency, and then use SPI to hop to the next frequency, and continue. Use the ATMEGA's digital output and interface that with with a raspberry pi's GPIO. I'd use say 5 RX chip/ATMEGA pairs to cover the relevant frequencies (if there's not enough GPIO pins I could use USB instead). So basically, the frequency+RSSI pair is constantly being sent to the Pi. Use the Pi (C++ or Python I guess) to monitor the RSSI of each frequency. If the RSSI is strong and relatively constant over a specified timespan (e.g. something that an analogue video stream would do rather than a wifi router), flag that as a (most likely) video transmission.

Does this sound feasible?