# notch rf filter

#### lev

Jul 1, 2012
9
Hi all
I checked out input given to me by (CD DRIVE) and found he is correct --I do have a decimal point error the problem signal is at 1470 KHZ sorry for the bad input

#### davenn

Moderator
Sep 5, 2009
14,178
Hi all
I checked out input given to me by (CD DRIVE) and found he is correct --I do have a decimal point error the problem signal is at 1470 KHZ sorry for the bad input

suspected so hence my insistance of checking the freq
14 kHz is extremey low.
you didnt answer my other question.... is this composite video or RGB ?

Dave

#### CDRIVE

##### Hauling 10' pipe on a Trek Shift3
May 8, 2012
4,960
Hi all
I checked out input given to me by (CD DRIVE) and found he is correct --I do have a decimal point error the problem signal is at 1470 KHZ sorry for the bad input
As you can see, it was Bob's keen eye that caught that.
Are you sure you do not mean 1470 KHz, that would be in the AM broadcast band.

Bob

Hi all
To answer a few inputs and questions
MY cable is a 75 ohm coax
The freq thats causing the problem is 14.7k it is not a decimal point error.
Once again, I thank each of you for your input and thoughtfulness
Im checking all input given to me

150 ft isn't a long run for 75 Ohm CCTV. The camera/source outputs over a volt of signal level. Do you have ab Ohmmeter so you can check continuity of your shield. If you wiggle the cable at either end does the picture change. Did you check that the 75 Ohm termination switch is on?

Jul 1, 2012
9
Hi Davenn

#### (*steve*)

##### ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,505
Hi all
I checked out input given to me by (CD DRIVE) and found he is correct --I do have a decimal point error the problem signal is at 1470 KHZ sorry for the bad input

#### lev

Jul 1, 2012
9
Sorry I am learning about these things one Item at a time

#### davenn

Moderator
Sep 5, 2009
14,178
150 ft isn't a long run for 75 Ohm CCTV. The camera/source outputs over a volt of signal level. Do you have ab Ohmmeter so you can check continuity of your shield.

no its not, but even a few 10's of feet let alone 150 ft is plenty to act as a wonderful antenna for a relatively close hi power local broadcast station (probably ERP'ing at least 5kW) and bring that signal straight into the video recording/viewing system.

The trick is now to notch the RF sigfnal without causing additional danage to the video signal.
The simplist experiment would be to try a couple of clamp on ferrite chokes, one at the output of the camera and one right at the input to the video equip. These would stop/lessen the RF that is flowing on the shield of the coax from entering either the camera or the video gear.

If that doesnt work well enough, then you could go to the L/C notch filter, this could be made on the end of a short length of coax and connected to the main coax feed via a BNC Tee connector.

Dave

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#### davenn

Moderator
Sep 5, 2009
14,178
I'm also pondering the use of an inline "trap" filter using a paralled capacitor and inductor. just looking for more info

Also contemplating that if a filter doesnt work, you may have to go to a 2.4GHz radio linked camera

Dave

Last edited:

#### CDRIVE

##### Hauling 10' pipe on a Trek Shift3
May 8, 2012
4,960
Transmission Line theory and design is an extensive subset of electronics theory. The ITT Radio Engineer Bible devotes a very large chapter to it alone. You can find lengthy text books devoted to nothing but Transmission Lines. A properly designed coaxial transmission line should not radiate, Likewise, it should not behave as an antenna either.

I like to think of coax as a water pipe. It shouldn't leak water out or in. That said. coax can't and won't do its job without excellent grounding and impedance matching at both ends. If possible, solid Gnd points along the line too. I'm not saying this is easy to do either.

Chris

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