Blocking AC

Thread Starter

obstacle89

Joined Oct 9, 2007
5
I realize that you can block the DC with a capacitor but that will still pass the AC. How can the AC be blocked out? I've heard you can place a capacitor in parallel with a half wave rectifier, would that work.
 

beenthere

Joined Apr 20, 2004
15,819
That is a hard question to answer, as you give no application. Diodes can rectify AC into DC, or, for a literal interpretation of "blocking", just open a switch.
 

roddefig

Joined Apr 29, 2008
149
Inductors are the usual tool to block AC, at least from what I've seen. You can use an inductor to feed power to an LNA in an active antenna over the RF signal. At each end you block out the RF using inductors.
 

Thread Starter

obstacle89

Joined Oct 9, 2007
5
The application is i'm trying to block out AC on my cable drop while allowing the RF to pass through to the modem. Wouldn't the inductance choke out the RF or distort it?
I appreciate the advice folks!
 

thingmaker3

Joined May 16, 2005
5,084
RF is AC. Are you trying to block the power frequency (50 or 60 Hz, depending on where in the world you are) and pass the signal? If so, you need a "high pass filter." You can read about them in our online textbook: http://www.allaboutcircuits.com/vol_2/chpt_8/index.html You might want to do some more basic study first, depending on your level of expertise. The sitemap is here: http://www.allaboutcircuits.com/l_sitemap.html

Optionally, if you are only interested in making the problem go away & don't care for the theory, you can buy a high pass filter for your cable modem for around five dollars US.
 

Thread Starter

obstacle89

Joined Oct 9, 2007
5
Thanks! I'll try out a high pass filter to block out frequencies less than 5Mhz since that is where my RF application starts at. Blocking out anything less would eliminate the presence of the AC or 60Hz low frequency energy. Am I reading that right?
 
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