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DC and RF Signal through same cable

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premkumar9

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Hi,
I want to take 12V DC through the same RF coaxial cable through which I take RF signal from the modulator O/P to channel combiner. I want to add the DC at the modulator side and take out the DC at the channel combiner side.How can I do it with out affecting the signal?
 

Hero999

Banned
It's possible but I wouldn't recommend it.

What frequency RF?

DC can be coupled via ferrite beads and small inductors to form an RF choke.

RF can be AC coupled using capacitors.

The DC side should have have a good low ESR/ESL capacitor across it to get rid of the RF.

This isn't a very good idea as it can leave yourself open to all sorts of EMC problems.
 

ericgibbs

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MikeMl

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It's possible but I wouldn't recommend it.
...
This isn't a very good idea as it can leave yourself open to all sorts of EMC problems.
Real world experience begs to differ: Millions of GPSs feed 5Vdc up the same coax as the amplifed ~2GHz signal is sent back down the same coax. Same with XM and Sirius receivers. Loran (100Khz) did it. TVRO distribution amplifiers do it. Hams use feedpoint preamps that do it. Etc
 

Nigel Goodwin

Super Moderator
Most Helpful Member
It's absolutely simple and commonplace, Sky satellite TV boxes even send DC power one way, and RF BOTH ways - and it's been standard practice for powering masthead amplifiers and cable repeaters ever since they first appeared.

You just need an RF choke and a capacitor at each end, 1mH and 1000pF used to be popular values.
 

Hero999

Banned
Real world experience begs to differ: Millions of GPSs feed 5Vdc up the same coax as the amplifed ~2GHz signal is sent back down the same coax. Same with XM and Sirius receivers. Loran (100Khz) did it. TVRO distribution amplifiers do it. Hams use feedpoint preamps that do it. Etc
Yes, I've seen it before, I have an aerial boost amplifier in by loft that uses it.

Yes, I suppose I was wrong, still it depends on how the voltage, current and what it's powering?
 
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