envelope detector

Status
Not open for further replies.
S

Spectacular Butter

New Member
Hi i just come out with this basic AM demodulator circuit with a low pass filter at fc=15khz and high pass at 159hz. It is for demodulating a 27mhz AM with 10khz information signal.

I know i am supposed to use LC filters which are more efficient for high frequency signals but i wanted to test this out using lab components which has very few inductors.

I am a beginner in this RF thing. So any comments would be very much appreciated.
 

Attachments

  • detector.gif
    2.6 KB · Views: 548

You would normally use a germanium diode for a demodulator, rather than a silicon one - simply due to the much lower voltage loss across them.

AM radio also doesn't have anything like the bandwidth you're hoping for, which is why it sounds so poor. If you're hoping to get 15KHz bandwidth from an AM radio you're going to be interfering over a good part of the spectrum!.

As a matter of interest, 15KHz is about the bandwidth from a VHF FM radio!.
 
This is a very low efficiency detector because of the signal loss over the diode. You can do a lot better by using 2 matched diodes as shown. This nearly eliminates the voltage drop over the detector diode. An additional inductor can be placed in series with D2 to reduce RF losses to GND. This 2 diode arrangement will also produce lower distortion.
 

Attachments

  • super_detector1.gif
    10.9 KB · Views: 507

My signal is not audio. It will be digital from the pc's RS232 port
 
Spectacular Butter said:
My signal is not audio. It will be digital from the pc's RS232 port
Click to expand...

That's even worse! - how fast are you hoping to use?, and what sort of modulator/demodulator (MODEM) are you planning to use?.
 
oh sorry for the lack of knowledge. How do i determine the bandwidth from the rs232 port? is it from the baud rate?

I planned to modulate it using an AM transistor modulator. Demodulate using diode detectors.
 
Spectacular Butter said:
oh sorry for the lack of knowledge. How do i determine the bandwidth from the rs232 port? is it from the baud rate?

I planned to modulate it using an AM transistor modulator. Demodulate using diode detectors.
Click to expand...

Perhaps you've noticed that telephone modems don't work like that?, that could be because there are good reasons for it!. A simple MODEM technique is to transmit two tones, one for 'One' and another for 'Zero', you can detect these at the receiver with a 567 PLL.
 
Status
Not open for further replies.

Similar threads

  • Question
How to make a traditional diode envelope detector radio receiver
2 3 4
Replies
78
Views
13K
Fluffyboii
G
120 vac Motion Detector Light Wanted?
Replies
11
Views
2K
Sophia Zeng
S
101 sequence detector using Verilog
Replies
0
Views
3K
PG1995
J
Phone ring detector circuit needed
2
Replies
20
Views
5K
jack0987
J
D
Model rail block detector to drive relay
2
Replies
29
Views
4K
Derekm
D
Menu
Log in
Register
Cookies are required to use this site. You must accept them to continue using the site. Learn more…