Question

[ajmix2]

What exactly is a blocking capacitor? I go to a vo-tech and my teacher showed us a simple amplifier circuit and said that there was a blocking capacitor in it. I'm just wondering what that is because he didn't explain it.
EDIT: Sorry i didn't read about the different categories. This is in the wrong forum i now know.

 

[Roff]

What exactly is a blocking capacitor? I go to a vo-tech and my teacher showed us a simple amplifier circuit and said that there was a blocking capacitor in it. I'm just wondering what that is because he didn't explain it.

A blocking capacitor is in series with the AC signal. A capacitor blocks DC current, but passes AC current. You may have learned that the reactance (impedance) of a capacitor is
Z=1/(2*pi*F*C),
where F is frequency. In this equation, note that if F=zero (DC), Z=infinity. Therefore, no DC current can pass. As F goes up, Z goes down. At some frequency, depending on the value of C, Z will be close to zero (relative to the load resistance), so the cap will look like a short circuit to AC at that frequency and all higher frequencies.

 

[audioguru]

Same question here too?

 

[Hero999]

Why didn't you ask your teacher?

Also beware that it isn't that simple, capacitors will become inductive at some frequency, from then onwards their impedance will increase. What's even worse is that there will be a point when the capacitive reactance and inductive reactance will cancel and cause it to resonate. This is why you wouldn't use a 100:mu:F electrolytic capacitor as an AC coupling capacitor at RF frequencies.

 

[quixotron]

A blocking capacitor is in series with the AC signal. A capacitor blocks DC current, but passes AC current. You may have learned that the reactance (impedance) of a capacitor is
Z=1/(2*pi*F*C),
where F is frequency. In this equation, note that if F=zero (DC), Z=infinity. Therefore, no DC current can pass. As F goes up, Z goes down. At some frequency, depending on the value of C, Z will be close to zero (relative to the load resistance), so the cap will look like a short circuit to AC at that frequency and all higher frequencies.

Thats my same response. In ECE 335, the instructor introduced blocking capacitors when designing common emitter/collector/base amplifiers for the DC section of calculating currents for BJT models.

Caps are a cheap way to smoke off dc.

 

[ajmix2]

Same question here too?

I post in multiple forums to get answers so i understand. Get a wide variety of answers...You know?

 

[quixotron]

I post in multiple forums to get answers so i understand. Get a wide variety of answers...You know?

Smart decision. Always confirm your answer. I noticed folks who finish exams first and don't check usually score on the lower left end of the bell curve.

 

[audioguru]

I post in multiple forums to get answers so i understand. Get a wide variety of answers...You know?

This site is the best one for accurate answers.
One forum has a moderator who don't have a clue and he gives wrong answers. Then that moderator deletes posts from anybody (me) who disagrees with him.

 

[Roff]

This site is the best one for accurate answers.

Except for the fact that I haven't been banned.

One forum has a moderator who don't have a clue and he gives wrong answers. Then that moderator deletes posts from anybody (me) who disagrees with him.

 

[audioguru]

I have never been banned from a forum. I was almost banned though for treating noobies like they were noobs.

 

[Hero999]

I probably would have been banned but I quit before he got chance to ban me.

 

[audioguru]

One guy got banned but I can't remember why. He came back with a new login name and admin didn't know.
Now Electronics-Lab gets about 50 SPAMs in one hour, all from the same person or robot.

 

[Hero999]

One guy got banned but I can't remember why.

Let me guess, because he disagreed with the moderator?

He came back with a new login name and admin didn't know.

They've never heard of IP addresses? That wouldn't surprize me.

Now Electronics-Lab gets about 50 SPAMs in one hour, all from the same person or robot.

If you ask me, most of that site is spam, the silly adverts clog the whole place up.

Electronics Lab has had its day, it used to be a reaonable site but now it's gone to the dogs.

Why do you still hang around there when you don't seem to think much of it?

 

[audioguru]

I hang around many electronics chat sites.
Usually the noobies do too.
The same questions at many forums.

 

[blueroomelectronics]

I still don't understand why Walters & Mstecha never returned... Their style was so err different that they would seem obvious if they had aliases.

You've got goobers over on EL like eplan** that even after 350plus posts is still clueless.

 

[audioguru]

Eplan** must translate everything he does (Iranian) so electronics is in the background. He wants to come to university in ******. If his government finds out he wants to defect then they will stone him or jail him.

MStechca is in Hamilton, Canada. His super-regen "radio" was able to pickup the sound from the very powerful channel 11 TV station up the hill from him.

I think Walters is a little American kid.

 

[blueroomelectronics]

Eplan** must translate everything he does (Iranian) so electronics is in the background. He wants to come to university in ******. If his government finds out he wants to defect then they will stone him or jail him.

MStechca is in Hamilton, Canada. His super-regen "radio" was able to pickup the sound from the very powerful channel 11 TV station up the hill from him.

I think Walters is a little American kid.

I could pickup CHUM radio in my fillings Actually I had a crystal radio I built as a kid and listened to Dr Demento when I was supposed to be sleeping.

As for Eplan** I wonder if he ever got his strange car alarm working.

And what's with SMS stuff in the middle east. I guess cell phones are free?

 

[audioguru]

CHUM FM was a classical music radio station that suddenly switched to acid rock! Now it broadcasts pop.

I haven't heard Ryerson-FM classical music for many years.

One time I caught CBC-FM playing stereo music with the channels out-of-phase. I called their engineer and he said he knows their mono is cancelled but there is nothing he can do about it.

 

[blueroomelectronics]

Sorry my crystal radio and fillings were AM only.

 

[audioguru]

Sorry my crystal radio and fillings were AM only.

You need to tip your head to one side so you slope detect FM transmissions with your AM detector. Like skiing.
Try facing the transmitter then try facing away from the transmitter.