RF Sensing - Switching Relay

[Ghpilot]

I need a circuit that will sense a 2 Ghz rf signal and turn off a relay and keep the relay
off as long as the signal is present.
Any suggestions or directions please.
Howie

 

[MikeMl]

Do you have a 2 GHz receiver, or are you asking how to build one?

 

[Ghpilot]

No I have a 2 Ghz signal source that I want to use to turn off a relay.

 

[MikeMl]

But it takes a receiver to detect a 2GHz signal in order to switch a relay. How many years are you willing to invest in learning how to build a 2 GHz reciever?

 

[Ghpilot]

All I want to do is sense an rf signal in the 2 Ghz range,then switch a relay.
Why do I need a receiver? This isn't a communication project.

 

[MikeMl]

Ok, lets play 20 questions...

What is the power level of 2 GHz source?
What kind of modulation on the 2GHz source?
What kind of antenna does it have on it?
What is the distance between the source to the relay?
Is there a cable between the source and the relay?
How long should it take to detect the 2 GHz energy?
What is the relay coil voltage? Coil current?
What does a Ghpilot fly?

 

[alec_t]

All I want to do is sense an rf signal in the 2 Ghz range

Then you need a receiver tuned to 2GHz. By definition, the thing that does the sensing is a receiver.

 

[Ghpilot]

Are you trying to be clown funny or just haha funny?
I hope I never get to the point in life where I can see thru a keyhole with both eyes.
It probably really hurts.
Take care.

 

[MikeMl]

Are you trying to be clown funny or just haha funny?
....

People come here for answers. They dont like the answers, they go away...

 

[cowboybob]

I need a circuit that will sense a 2 Ghz rf signal and turn off a relay and keep the relay
off as long as the signal is present.
Any suggestions or directions please.
Howie

Howie,

First, welcome.

If I understand your question (and subsequent responses) you might wish to consider this chip, for starters. Note that it is called a "detector". No doubt there are simpler solutions. This is just the first datasheet option I came across when I googled "schottky diode 2GHz to 3GHz".

By carefully constructing your 1/4λ antenna to 2Ghz (≈3.75cm in length) you could roughly "tune" the circuit to your 2Ghz signal. It would still respond to other frequencies, but not as well. Plus the power level of your transmitter, as well as the range from transmitter to receiver chip antenna, would be critical factors in overall operation.

As this chip will only provide a max of a 2mA output pulse, you'll need a buffering circuit to turn off a relay as you describe.

All I want to do is sense an rf signal in the 2 Ghz range,then switch a relay.
Why do I need a receiver? This isn't a communication project.

But you are, in fact, detecting (receiving) a signal, are you not, that hopefully, once "sensed" will be "communicated" as an "OFF" command to the relay, right? Simple, to be sure, but communications nonetheless.

 

[Ghpilot]

Coyboybob:
Hey thanks for the reply. I realize that my parameters are somewhat limiting and possibly
very difficult to achieve.
I guess the word sensing should have been detecting to put this in correct terms.
My electronics language terminology is rusty.
After detecting the rf with this chip I could use an opto isolator and control the relay on the other side. So a few ma output may be enough.
In terms of frequency, not sure on exact frequency. I believe it is fm, not sure of deviation. Again this would dictate front end design.
I'll need to measure these before starting project.
The purpose of this post was to get the general ideas and parameters that I would need to address before working on the project.
Thanks again for your input,much appreciated.
Take care,

 

[cowboybob]

Just a couple of quick notes, Ghpilot.

The output of the LTC5505 won't drive an opto isolator but it would trigger a simpe transistor switch that could drive any number of things.

Even if the signal is FM, the deviation should not be a problem in this case.

You might note as well that, although the chip is only $1.22USD, they have demo boards for sale (pricey [$100USD]), but with a good enough project definition they do occasionally give them away. Call your regional rep. Worked for me with an extremely low voltage (40mVDC) energy harvesting chip/demo board. Good guys to work with.

And they're TSOT-23 SMD's, which is to say really, really small chips (2.9mmX1.5mm). VERY tiny and difficult to manipulate.

Good luck.

 

[Lighty]

Hi Ghpilot,

As cowboybob stated, you would have to buffer the output, even the opto coupler would draw too much current.

You could used an Op-amp to buffer the output, and then use the opamps output to drive a transister which in turn controlls the relay.

Best of luck

 

[ccurtis]

You can put a filter in front of that detector, like this one, to prevent signals at other frequencies from tripping the detector: https://www.electro-tech-online.com/custompdfs/2013/03/AFS14A15-201750-T2.pdf

You may want to put an amplifier in front of the filter, or the filter in between two amplifiers, such as https://www.electro-tech-online.com/custompdfs/2013/03/ERA-51SM.pdf, depending on the signal level.

 

[MikeMl]

You can put a filter in front of that detector,...f[/url]

You may want to put an amplifier in front of the filter...

Gee, it sounds like you are building a receiver...

You also need to understand how to run a path-loss calculator, like this one, to see if the LTC chip will detect your signal..., at what power level, antenna gains, feedline losses, and distance...

If it were me, I'd be looking for a ready-made receiver, or hacking a WIFI.

 

[Ghpilot]

Call it a receiver if you want but all I'm doing is sampling for rf, and controlling a relay with that signal.
Thanks ccurtis for your info,I'll have to see if I need it.
Distance from xtrmr to recvr antenna is very short distance so hopefully there would be little stray rf to trip it.
Filtering maybe needed once I get a better idea on freq.
Thanks for your info