Bandstop (notch) RF Filter question.

Do a google search on "Bridged-T filter". They can easily be made to separate parts of a video signal, or even interference between the audio and video carriers. ;-) It shouldn't be too hard to de-tune one to cover a whole channel.

A bridged-T will be plenty sharp enough for your needs.

Thirty years ago I made one for channel 5 that passed the audio and video and suppressed everything (40-50db down, IIRC) inbetween.

You might get a better response from sci.electronics.design than here though.

On Sun, 9 May 2004 09:33:45 -0400, KR Williams put forth the notion that...

This brings up a question I've had for some time now. Is there a way to filter out whatever signal networks or local stations ad that inserts the station ID "bug" in the lower right hand corner? How about the scrolling marquis, pop-up banners and other assorted garbage that some stations think is so cute? TV's starting to get as annoying as a lot of web sites.

Sure. Duct tape.

On Sun, 9 May 2004 11:40:09 -0400, KR Williams put forth the notion that...

If I did that, my 36" TV would probably be closer to a 24" when I got done.

i found a few pdfs with the gritty of these things. they look like what i want. :D

'm a little lost when it comes to inductors thou. never did stuff with rf. I'll hack my way thru it. thanks.

What the world really needs is a way of detecting the presence of the tumor on the bottom of the screen and using it to make a fool-proof commercial killer. Notice - no tumors during the ads!

Myself, I prefer to watch DVDs - some times I even put them in the player.

Bill

Nah, measure it. The point is that a "filter" isn't going to get rid of that crap. He only thing that will is turning the damned thing off. Sooner or later they'll get the message. Until then, suck it up. They "control the horizontal" and they "control the vertical". ...get used to it, or turn the damned thing off.

They may tricky to tune sharply (though you don't need what we were looking for), without some expensive tools. A friend used some rather expensive HP network analyzers and I did it in the time-domain with the help of an even more expensive Tek Signal- Processing-System. Cool stuff! ...but that was 25 years ago, so it's likely a $.10 deal now. ;-)

Yea, Initial tests are not going well. It seems that i can only induce static across 15 channels with the center one almost blocked out (i'd guess around -15 to 20 db at center). i'm starting to tweak componets but not sure which is responsible for how wide the notch is. not having an o.scope or any of those exp. toys is a bit annoying, but i'll just tweak until i get it right.

Just for referance, correct me if i'm wrong (because i'm guessing), the resistor is what decided the -db level at center freq, the 2 caps are what decides the width of the blackout area and the inductor tunes it? :-/ i hate not having an o.scope.. then i could just see what is happening.

fixed pitch ascii art. --------L1------- In ____| |____Out | | -----C1----C2---- | R1 | ----- --- -

Well, you really have to be able to measure filter response to be able to tune such.

Good luck! Trap filters are tricky, since they're very selective, which is what you wanted.

It's been a *long* time since I did this stuff (30 years or so). The resistor is what makes it a "bridge". The resistor is used to balance out the 'Q' of the inductor. IIRC, the inductor we used was a couple of turns of 14GA buss-wire around a 3/8" drill bit form (high tech here, I know), the resistor a few hundred ohms, and a couple of 30pf mica caps, but it's been many years. The inductor is squozen to tune.

That's the one, but notice the series L1 parasitic in the equations.

Hell, I'm lucky I remembered the name of the filter (and others have told me I'm all wet)! ;-)