Measuring the strength of a signal

Go To Last Post
20 posts / 0 new
Author
Message
#1
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Hi buddies
I don't know much about signals. but I have to create a circuit preferably with AVR controllers to measure the strength (quality) of a signal.
How can I measure the strength of a signal basically?? shall I measure its Voltage? its Current? or some other parameters of that?
P.S my signal is WiFi 2.4Gh
Thank you for your help in advance

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

For an RF signal I think it's just the voltage, the impedance is already known and fixed, so power can be computed.

Most transceivers have a dedicated register to read out RSSI; Relative Signal Strength Indication.

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

jayjay1974 wrote:
For an RF signal I think it's just the voltage, the impedance is already known and fixed, so power can be computed.

Most transceivers have a dedicated register to read out RSSI; Relative Signal Strength Indication.

I am really sorry but I didn't understand what do you mean by "Most transceivers have a dedicated register to read out RSSI" How can I do that in practice?

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Moved to General Electronics forum

A GIF is worth a thousend words   They are called Rosa, Sylvia, Tricia, and Ulyana. You can find them https://www.linuxmint.com/

Dragon broken ? http://aplomb.nl/TechStuff/Dragon/Dragon.html for how-to-fix tips

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

You can use AD8361

[url]http://www.analog.com/en/rfif-co...

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

The OP has a major problem, here. What he or she wants to do is actually quite hard. Here is why:

The voltage created at the output of an antenna is very small - microvolts, to, at the very largest, millivolts. Further, it is composed of many signals at many frequencies. For example, if there are local FM or TV stations, those signals will also be mixed in. The antenna will provide a little "filtering" based on its length, but this is not enough to keep out other signals.

So, the second thing that is needed, after the antenna, is some kind of frequency selector. A tuned circuit is common. Now, however, we get to a sticky point. WiFi operates on two widely separated frequencies - 2.4GHz and around 5.0GHz. This makes it quite hard to use ordinary tuned circuit filters. Also, the 5GHz frequency is high enough that conventional inductors and capacitors do not work well.

Then, you have to deal with the very small signal voltages. Even the broadband power detectors (Analog Devices, Maxim, Linear Tech, and others) are not sensitive enough unless you are very close to the transmitter.

So, how do people do it? The simplest way is to built a real WiFi receiver with one of the chipsets. Use the RSSI (Received Signal Strength Indicator) output. Depending on the chipset, this may be an analog voltage or it may already be digitized. If analog, then use any garden variety ADC. If digital, then set up your SPI or I2C link to access the value in one of the internal registers.

It should be pointed out that the receiver chip solution is not without its own problems. The chips tend to have quite a few pins at a very small pitch, almost always SMT. The antenna matching circuit has its own challenges though the chip reference design often has the components figured out for common situations. You MAY be able to find a dev board from some place such as SparkFun that has the chip mounted, with an antenna, and provides access to RSSI.

Jim

 

Until Black Lives Matter, we do not have "All Lives Matter"!

 

 

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Strength != Quality.

Four legs good, two legs bad, three legs stable.

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Absolutely correct....

The OP did not ask for quality, only "strength".

Jim

 

Until Black Lives Matter, we do not have "All Lives Matter"!

 

 

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

WiFi Keychain Signal Strength meter with bargraph LED readout, 4.14 EUR, $4.95 USD.

Done.

Less expensive than anything one can build in small quantities.

http://www.dealextreme.com/p/wif...

JC

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Absolutely...

Unfortunately, the OP asked for something that would work with an AVR. Guess if you used one of the AVRs with built-in USB interface and ran it as an OTG device.

Jim

 

Until Black Lives Matter, we do not have "All Lives Matter"!

 

 

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Hack the $5 keychain gadget. Remove the bargraph, and attach an AVR there instead. Read out the signal strength and display it on a bargraph attached to the AVR (the builder probably has one lying around quite close...). :wink:

Seriously, this would probably be a better thread if the OP stated if this is e.g. an idea for a product, a school assignment, a hobby project, something involved in a bet, or..

As of January 15, 2018, Site fix-up work has begun! Now do your part and report any bugs or deficiencies here

No guarantees, but if we don't report problems they won't get much of  a chance to be fixed! Details/discussions at link given just above.

 

"Some questions have no answers."[C Baird] "There comes a point where the spoon-feeding has to stop and the independent thinking has to start." [C Lawson] "There are always ways to disagree, without being disagreeable."[E Weddington] "Words represent concepts. Use the wrong words, communicate the wrong concept." [J Morin] "Persistence only goes so far if you set yourself up for failure." [Kartman]

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

In fact the OP has expressed the question in such a way as to suggest he/she is a troll. P.S.ing that the signal is wifi is an artistic touch.

P.S. Signal strength is proportional to the DC output of a high frequency rectifier, like in the old crystal AM radios. It various according to amplitude modulation. Bandwidth and phase modulation signal/noise are more useful nowadays.

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Not that difficult.

OP didn't spec what resolution the signal strength needed to have.

(And a little preliminary testing will probably show that the signal amplitude varies greatly over time and exact positioning of the sensor, so that only a few levels are even meaningful.)

If he so desires the micro just reads the LED bar graph signals.

JC

Edit: Cross posted with the above. I started the reply and got interrupted for a few minutres...

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

ka7ehk wrote:
Absolutely correct....

The OP did not ask for quality, only "strength".

Jim

I beg to differ.

From OP:

Quote:
I don't know much about signals. but I have to create a circuit preferably with AVR controllers to measure the strength (quality) of a signal.

Four legs good, two legs bad, three legs stable.

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Hey dear friends
Thanks for replies. Let me speak more clear. I am going to design an Antenna tracking system. this antenna has 5 different WiFi beam on that. I have a flying object which i want to communicate with (Point to Point). In order to do this I have to track the location of that object. I have read in an Article that they had used these beams to find out where is the location of that flying object. How? they measured the strength of that 5 beams (the picture is attached here) if the left beams have more strength so the flying object is going to left. if the strength of right beams are higher so the flying object is going to right and so on. Now what I want is that how to measure the strength of these beams??

Attachment(s): 

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Is this for a commercial product? Or is it for hobby or research? Or, military?

Jim

 

Until Black Lives Matter, we do not have "All Lives Matter"!

 

 

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Everything new is old ... Google "metox wind finding rawin"

Ross McKenzie, Melbourne Australia

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

ka7ehk wrote:
Is this for a commercial product? Or is it for hobby or research? Or, military?

Jim

Jim this is a kindda both Hobby and Research :)

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Not entirely sure what the drawing is showing, but if it shows a number of modules with antennas facing outward, they are in the wrong orientation. The antennas need to be directed toward the reflector.

I'd go for 5 prebuilt modules that report signal strength either as part of a data stream or as analog values.

Jim

 

Until Black Lives Matter, we do not have "All Lives Matter"!

 

 

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Quote:
Thanks for replies. Let me speak more clear. I am going to design an Antenna tracking system

If you want To use The RSS just To point The antennas to the object is one thing but if you want to localize the object is completely different (not easy)..

First thing to have in mind, antennas's radiation pattern, how will be it on your object? Does your object will go up side down, if yes it's a problem.
That little gadget, wifi detection, how is radiation pattern? Uuuu, hard question.. ;)

As others said, build an RF RSS circuit isn't an easy task, so the best way is to get the RSS values of an ready transceiver..

Regards,

Bruno Muswieck