3 MHz RF and feed 12 DC on same signal cable

[Francisco Xavier]

Hi subcribers and Carl,
I was using before a remote B&W CCD and 100 m common wire (4 conductors) to feed DC and send the video back (w/RC filtering).
Now I will like to use coaxial cable (2 cond.) to feed CCD and send 3 MHz video signal back by same wiring.
Is it enought to decouple DC using capacitors (in serial) on both ends ? Wich values for this capacitors?
If somebody knows some board design for this pourpose I will thanks.
Best regards,
Francisco Xavier

[Sean Goddard]

Re: 3 MHz RF and feed 12 DC on same signal cable

You would need to put an inductor in SERIES with the tapped off 12V, at the FAR END of the feed coax, i.e. the end to which the piece of equipment using the 12V is. This will stop the 3MHz getting onto the supply of the target device.

ALSO, be sure to use plenty of decoupling caps (100nF) on all the supply rails of the target device.

[Francisco Xavier]

Re: 3 MHz RF and feed 12 DC on same signal cable

Hi,
I look site after site on WWW to find one and just found Bias Tee. Last weekend spent all days and night. Bias tee change the video signal on very worst way I could not use it. After experiences I found the 10 uF electrolitic capacitor is the best to decouple video signal (not degrade it) but when I couple/decouple de DC with inductor, the video signal goes away.
I use one tee on both ends of coax near the CCD and monitor.
If you know some wworking schematic to improve my pourpose please let me know. I have not space enought inside de housing to put a batery to feed the CCD.
I will thanks any help.
Greatings
Francisco Xavier

[Router]

Re: 3 MHz RF and feed 12 DC on same signal cable




Try this configuration using the values you have.

Inductor should be about 2mH or so. You might also want to put ANOTHER cap on the INPUT of the DC and the OUTPUT of the DC TO the unit to be powered.

Try using a NOT polarised electrolytic. Yes you can get them.

[Francisco Xavier]

Mesage to Mr. Router - Video and power on same wire

Hi Mr.Router
Pardon to insist on the subject. But have you tested this design on a black&white CCD video signal?
The problem I found the video signal from a CCD is about 3 MHz wideband (quite from 1 Hz to some MHz) and the capacitance and more the indutance change the video signal shape (the lowest frequencies are more permeable throu the indutance) and with the same design (w/ lesser indutance values and 10 uF electrolitic) the video signal was gone and some times I have it very deformed.
Thanks you your help.
Francisco Xavier

[Router]

Re: Mesage to Mr. Router - Video and power on same wire

Hi Xavier,

I haven't PERSONALLY tested it, but it is a well used and tried circuit.

I have seen it used many times before.

Maybe your set up is different, or there's an impedence matching problem.

I'd have to see your system to sort it out.

[Francisco Xavier]

Re: 3 MHz RF and feed 12 DC on same signal cable

Thank you Mr.Router
I have now the video and DC running on same coax cable. The indutance and capacitance values are critical. Even so I had to reajust the impedance w/ potenciometer (1K).

Francisco Xavier