2
\$\begingroup\$

I have previously used the NRF24L01 to transmit data between two microcontrollers. I have also used other radio transmitters and they all work great.

For purposes of learning I want to create a very simple radio transmitter. I do not want to get into the trouble of decoding the frequency into 0s and 1s. I just want to send a frequency over the air and capture it with an oscilloscope. If I create something like this will it work:

schematic

simulate this circuit – Schematic created using CircuitLab

On the left part I have a device that generates a 1 GHz pulse. That pulse is connected to a cable and the cable to an antenna.

On the right I have an antenna connected to an oscilloscope. Will the oscilloscope on the right read 1 GHz?

Lastly how large will my antenna have to be in order to capture a 1GHz radio signal?

Note I don't mind using a 433Mhz pulse instead than 1Ghz to make it easier. I am assuming 1Ghz will be easier because I don't want to have a large antenna

Reason why I want to do this:

I want to do this for purposes of learning and also because I have a project that runs from a battery. In order to save battery Arduino wakes up for 30ms in order to listen for a command. So it awakes listen for radio packets for 30ms and then go to sleep for 2 seconds. If I want to send a command to this receiver I will have to send pules every 5ms for up to 2 seconds. The reason why it takes so long is that the NRF24L01 takes 10ms to initialize then I have to send the listen command etc everything through ISP. It will be nice if I could have control of that myself in order to sleep for shorter amounts of time.

I still plan on using the NRF24L01 to transmit data. I just want to build something that will enable me to wake up my receiver fast. If my receiver is awake all the time then my battery will not last. I need a solution where my receiver wakes up for 2ms to check to see if it needs to become awake and then go to sleep for 1s..

\$\endgroup\$
5
  • \$\begingroup\$ "I just want to send a frequency over the air and capture it with an oscilloscope". If you explain the purpose of this, you may get better answer/solution. BTW, I had to do very similar experience to replace NFC with Ghz radio (though, I did not like that idea). I just used some available radio, RF oscilloscope, spectrum analyzer, directional antenna, 4Ghz RF amplifier, and etc in a large shilded cage. The total equipment costed a couple of hundred thousand dollars (I didn't care for it was free rental). If you want to detect 1nS pule over the air, that would be a very interesting project. \$\endgroup\$
    – jay
    Commented Aug 12, 2021 at 21:27
  • \$\begingroup\$ I will explain the reason why I want to do it on my edit @jay. Posting it now... \$\endgroup\$
    – Tono Nam
    Commented Aug 12, 2021 at 21:32
  • \$\begingroup\$ Thanks Bro! That is an interesting question, I would need that, too, sometime. Have you spoken to Nordic yet? I am not sure about these though: Is the chip a SOC containing ARM processor (cortex M4 or similar)? If so, you have a great chance to solve your dilemma quick, sleep/wake-up. Meantime, I don't think a digital pulse can do much. Let's hope someone comes up with a good advice. \$\endgroup\$
    – jay
    Commented Aug 12, 2021 at 22:06
  • 1
    \$\begingroup\$ Do you really have a 1 GHz DSO? \$\endgroup\$ Commented Aug 12, 2021 at 22:29
  • \$\begingroup\$ No @TonyStewartEE75. I was reading about antennas and how they work. I though it was going to be simple to read and make such a high frequency. I am learning its not that simple so I will probably have to go to 433Mhz or lower. \$\endgroup\$
    – Tono Nam
    Commented Aug 12, 2021 at 23:15

2 Answers 2

2
\$\begingroup\$

Will the oscilloscope on the right read 1 GHz?

Theoretically, if you set everything up right (correct impedance matching on both sides, antennas have the correct polarization, you transmit with enough power, the oscilloscope can measure frequencies that high, etc) then yes you will get a 1 GHz reading on the oscilloscope attenuated based on the distance between the two antennas.

Lastly how large will my antenna have to be in order to capture a 1GHz radio signal?

This depends on what type of antenna topology you want to use. For your application it would be simpler to have an omnidirectional antenna which means the minimum length is 1/4 wavelength of the signal provided the ground plane it is mounted to is at least that size in one direction (7.5 cm). Otherwise you’ll want a half wave antenna (15 cm). Omnidirectional antennas are generally simpler and send a broadcast signal in all directions, but they have less gain than other types of antennas so your transmitter and receiver will need to be closer together.

A side note on the frequency choice: In the U.S., the 2.4 GHz range used by the NRG24L01 is an ISM band that is free to use for the public at low enough powers. The 1GHz band however is used for airplane and ship navigation which is something the FCC doesn’t want people messing with and could get you into trouble if you’re not careful. 433 MHz would be safer if you’re in the US.

\$\endgroup\$
3
\$\begingroup\$

Antenna efficiency will be proportional to length up to 1/4 lambda.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.