FSK Demodulation: Testing Code Without Receiver/Radio

  • Thread starter Thread starter kshitij14395
  • Start date Start date
Click For Summary

Discussion Overview

The discussion revolves around testing code for FSK (Frequency Shift Keying) modulation using a transmitter (ADF7021-N) at 145 MHz without access to a receiver or radio. Participants explore methods for verifying the code's functionality, including the use of an oscilloscope and considerations regarding legal and safety aspects of transmission.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions the viability of using an oscilloscope for testing the code without a receiver, seeking alternative methods.
  • Another participant inquires about the frequency range of the carrier signal, suggesting that it may jump among multiple frequencies.
  • Concerns are raised about potential interference with licensed radio frequencies, particularly regarding the 145 MHz band in the U.S.
  • A suggestion is made to use a dummy load to avoid actual transmission while testing.
  • A method for FSK demodulation called "slope detection" is proposed, involving the use of a sharply tuned filter to observe changes in amplitude during modulation.
  • There is a recommendation to consider using a PLL (Phase-Locked Loop) for more refined decoding in future circuit designs.

Areas of Agreement / Disagreement

Participants express concerns about legal and safety issues related to testing at 145 MHz, indicating a general agreement on the need for caution. However, there is no consensus on the best method for testing the code, with multiple approaches and techniques being discussed.

Contextual Notes

Participants highlight the importance of licensing and safety when testing transmitters, as well as the limitations of using an oscilloscope for this purpose. The discussion includes unresolved technical details regarding the implementation of the proposed demodulation methods.

kshitij14395
Messages
1
Reaction score
0
I have a transmitter(ADF7021-N) that I've programmed to transmit data at 145Mhz. I wanted to verify whether my code is right or not. however due to the unavailability of a receiver or radio, I decided to check my code using an oscilloscope, but received no concrete results. Is my concept viable or are there other ways to test this code?
 
Engineering news on Phys.org
Hi kshitij14395. I see you are new hereabouts. http://imageshack.com/a/img515/4884/welcomesign.gif

Are you saying you have a carrier that basically jumps around among 4 or 5 known frequencies? What is the lowest and the highest of these frequencies it will have?
 
Last edited by a moderator:
kshitij14395 said:
I have a transmitter(ADF7021-N) that I've programmed to transmit data at 145Mhz. I wanted to verify whether my code is right or not. however due to the unavailability of a receiver or radio, I decided to check my code using an oscilloscope, but received no concrete results. Is my concept viable or are there other ways to test this code?

Welcome to the PF.

Do be a bit careful when testing your transmitter. What band is 145MHz in your country? You need to be sure not to create interference with other licensed radios in your area. So testing with only a coax cable from your transmitter into the 50 Ohm termination of your oscilloscope is probably a good idea.

What oscilloscope do you have? Can it do FFTs? Can you store part of the waveform and export it as a file to run an FFT on with your PC?
 
First, I would agree that you need to check your licensing...145 MHz is in the middle of the 2-meter amateur band in the U.S. As long as you don't actually transmit (such as using a dummy load) that wouldn't be a problem...but be safe.

The simplest FSK demodulator is "slope detection", or what i like to call "slop" detection. Use a sharply tuned filter tuned slightly off center from the unmodulated carrier. As you modulate the carrier, you should see a change in the amplitude. Look up "discriminator" on the web for more details.

When you're ready to polish your circuit, you'll probably want to use some kind of PLL for decoding.

Eric
 
  • Like
Likes   Reactions: 1 person

Similar threads

Where is the demodulator in this AM receiver?
  • · Replies 12 ·
Replies
12
Views
3K
Trying to triangulate position of rogue radio transmitter.
  • · Replies 20 ·
Replies
20
Views
16K
How to automate tests on a physical model without real data
  • · Replies 4 ·
Replies
4
Views
1K
Is there a way to prevent T1 stress tests from keying all radios at once?
  • · Replies 2 ·
Replies
2
Views
2K
How can RLC circuits and LCAM be used together to demodulate AM signals?
  • · Replies 15 ·
Replies
15
Views
6K
Time for radio signal to get to a receiver
  • · Replies 2 ·
Replies
2
Views
2K
Why is my PIC 18F2550 not sending data when I tell it to?
  • · Replies 6 ·
Replies
6
Views
2K
Why Does My PIC16F723A Show a Programming Error in MPLAB X?
  • · Replies 2 ·
Replies
2
Views
3K
How can I improve the range of my AM transmitter?
  • · Replies 10 ·
Replies
10
Views
5K
Can Short Pulse Bandwidth Limitations Be Overcome in Radio Transmissions?
  • · Replies 16 ·
Replies
16
Views
3K