My spectrum analyzer

Thread Starter

mik3

Joined Feb 4, 2008
4,843
hi guys,
I posted my homemade spectrum analyzer on my blog with links in youtube to see it in action. I posted the schematics too. If you are interested see it and tell me your opinion. Thanks
 

SgtWookie

Joined Jul 17, 2007
22,210
What are esoteric components?
Little used, difficult to understand, difficult to obtain, etc.

Sometimes it seems that people use such components just to impress other people how "smart" they are. Meanwhile, such things can unnecessarily create a lot of difficulty and frustration for people attempting to replicate the circuit.
 

Audioguru

Joined Dec 20, 2007
11,249
There are much better opamps than the lousy old LM324. Its half voltage output is a max of only 6kHz. Better opamps go to 100kHz at full voltage output.
The TL074 (7V minimum supply) and MC34074 (3V minimum supply) are good.

I think the 10uF filter capacitor after each rectifier "will take all day" to charge. I would use 0.1uF and a 1M discharge resistor.

The half-wave rectifier charges the coupling capacitor when it shouldn't. It should use two diodes, not one.

The dynamic range is not much because the rectifier chops off anything with a level below 0.7V peak. The rectifier should be an active rectifier with an opamp cancelling its 0.7V loss.
 

Thread Starter

mik3

Joined Feb 4, 2008
4,843
The half-wave rectifier charges the coupling capacitor when it shouldn't. It should use two diodes, not one.
This is not the best design, its an easy and cheap design i made just for hobby. I know it could be done better.

What do you mean by the above comment you said?

How should i connect this two diodes?
 

Audioguru

Joined Dec 20, 2007
11,249
What do you mean by the above comment you said?

How should i connect this two diodes?
With a single rectifier diode then the output coupling capacitor C3 becomes charged then the rectifier doesn't work anymore. R8 helps but its value is too high. Adding a diode discharges C3 on each cycle so the rectifier continues to work.

Why does your schematic have measles dots all over it? Multisim?
 

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Thread Starter

mik3

Joined Feb 4, 2008
4,843
With a single rectifier diode then the output coupling capacitor C3 becomes charged then the rectifier doesn't work anymore. R8 helps but its value is too high. Adding a diode discharges C3 on each cycle so the rectifier continues to work.

Why does your schematic have measles dots all over it? Multisim?
The diode you propose to use is useless because the output of the bandpass filter swings almost between 0 and 5 volts, so this diode never contacts. The capacitor discharges through the op amp. The ouput signal of the bandpass filter swings around 4.3 V and C3 in combination with R8 form a high pass filter with a cutoff frequency of 1 Hz as to remove the DC component from the output signal of the bandpass filter. Thus, we have only an AC signal across R8 and the rectifier works.

The dots are there because i converted the captured BMP picture into a JPG format.
 

Audioguru

Joined Dec 20, 2007
11,249
In your circuit, C3 gets charged more and more with the signal until it doesn't work properly anymore.
In my circuit, the added diode discharges the extra DC across C3 on every cycle so it continues to rectify properly.
 

Thread Starter

mik3

Joined Feb 4, 2008
4,843
In your circuit, C3 gets charged more and more with the signal until it doesn't work properly anymore.
In my circuit, the added diode discharges the extra DC across C3 on every cycle so it continues to rectify properly.
I thought of it more and you are right because the discharge time is greater than the charging time so we need to put the diode you suggested to reduce the discharge time. That's why i like this site, we all learn form each other.
 
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