AM detector help needed

Thread Starter

elrhazouani

Joined Feb 8, 2011
15
thank you for referencing the Mouser website.Should I be carefull in selecting the transformers because they have different turns on the primary and the secondary?
 

Adjuster

Joined Dec 26, 2010
2,148
Clearly the turns ratios are important. The transformers have to suit the impedance conditions in your circuit, or alternatively your circuit will have to be adjusted to suit the available transformers.
 

KL7AJ

Joined Nov 4, 2008
2,226
I am working on radio project for school. We we given a whole circuit to test. My question is that I want to change the detector circuit (AM envelope detector) with a better one. Any suggestions will be much appreciated.

Yes....you want to use a synchronous detector, which is far more linear. Many references to synchronous detectors on the Internet





Eric
 

Adjuster

Joined Dec 26, 2010
2,148
That's pretty much it. The main problem is getting that carrier in the first place! In a synchronous detector, a reference signal, typically from a local oscillator phase locked to the incoming carrier, is used to mix with the signal. This is not not linear mixing, but a process of modulation or switching, such as occurs in as in a superhet frequency changer, except that in this case there is zero beat frequency, so that the baseband modulation signal is obtained. This can be done using a variety devices from BJTs, FETs to multiplier circuits or transmission gates.

This contrasts with an ordinary AM detector where the signal voltage itself effects its own switching, according to the non-linear response of a diode or some other device, in more or less of a rectification process. The synchronous detector is particularly useful in cases where higher levels of noise or other interfering signals are present. It can also be used to demodulate more complex modulation schemes than simple AM, which a plain diode detector cannot do.

Unfortunately the synchronous detector's advantages all hinge on providing a clean reference signal which reliably stays in step with the carrier, even for instance when the signal is subject to fading. If synchronisation is lost, as it must be when tuning between different signals, some means must be found to manage the loss and reacquisition pf synch, perhaps using "squelch", or most unpleasant noises may be heard.
 

Thread Starter

elrhazouani

Joined Feb 8, 2011
15
I'm trying to use the IF transformer for tuning. However, I do not know how to breadboard it. I want to use it in junction with a capacitor to tune for a range of frequencies between 1230khz and 1530khZ. I am using something similar to the piece found in this link:
http://www.mouser.com/catalog/specsheets/164261.pdf
I do not know what output to take to the If amplifier, and what end to ground, which side the capacitor will go and on what pins. also what capacitor value is best for the aimed range of frequencies?I only need single input/output
thank you all for your help.
 

Audioguru

Joined Dec 20, 2007
11,249
I'm trying to use the IF transformer for tuning. I want to use it in junction with a capacitor to tune for a range of frequencies between 1230kHz and 1530kHz.
The local oscillator frequency and RF amplifier's tuned frequency are changed in a super-heterodyne radio, the IF frequency does not get changed.
The IF frequency of most AM radios is 455kHz.

Your Mouser link does not work.
 
Top