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Send Audio Signal Longer Distance

Suraj143

Active Member
I have a CCTV microphone unit & its audio output is a RCA out (Line out) Output Level is (0-6Vpp).I want this audio to be delivered to a DVR Audio IN which is placed over 80m.Now I have wired a coaxial cable RG59 & there is so much humn/noise.

How to send "Lineout audio signal" over longer distance?
 

ronsimpson

Well-Known Member
Most Helpful Member
You have hum and noise on the shield of the coax.
Search for "audio isolation transformer balanced unbalanced".
There are little boxes that on the receiving end may remove the hum. "balanced to unbalanced"
If that alone does not work then you may need the opposite on the end of the cable.

Audio cable for long runs: Note two shielded wires.
1610027120165.png
For long distance audio we use a coax with two wires inside the shield. The first transformer takes the "audio" & "ground" in and makes Ground, Audio & Not_Audio. (signal and the inverted signal) On the receiving end noise is on all three wires. The transformer takes the Signal & Inverted Signal and substrates them to get 2xSignal with out noise. The noise on the black wire and noise on the white wire are also substracted and = "0"
1610027177179.png
 

audioguru

Well-Known Member
Most Helpful Member
I think the microphone preamp has a balanced output signal plus a grounded shield but your TV cable has only one unbalanced wire inside its shield.
Microphone cables usually have two wires inside its grounded shield.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
80m line level audio using unbalanced cable shouldn't be an issue? - I suspect his problem is that he's using RF coax and not audio coax, with RF coax not providing much screening at all at audio frequencies.
 

Beau Schwabe

Active Member
About 20 years ago, I used the method posted in #2 to run under the crawl space of my house to go from the bedroom (PC where sound was originating) to the living room (where the Stereo system was). About 100 feet without any detectable noise.... Although I didn't use COAX, I just used two audio isolation transformers wired back to back over a distance for each channel with standard Phono cables. ie. for each LEFT and RIGHT channel : LINE-OUT from PC to transformer on one end ... on the other end transformer to AUX-IN on the Stereo system with just twisted pair wire in between the transformers ... no shielding.
 

audioguru

Well-Known Member
Most Helpful Member
Yeah, I have never tried TV coax cable for audio signals. I have always used audio cables for audio but some cables had a very poor shield.
 

Suraj143

Active Member

audioguru

Well-Known Member
Most Helpful Member
A transformer provides a balanced signal but your coax cable is unbalanced.
 

crutschow

Well-Known Member
Most Helpful Member
A transformer provides a balanced signal but your coax cable is unbalanced.
If you ground one side of the transformer output and ignore the center-tap, then it will be a single-ended unbalanced output, which should drive the coax fine, especially at audio frequencies.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
If you ground one side of the transformer output and ignore the center-tap, then it will be a single-ended unbalanced output, which should drive the coax fine, especially at audio frequencies.
And what does that achieve? - the existing line output will already drive the coax fine.

The issue here (as I see it) is that he's not using audio screened cable, adding transformers isn't going to make any difference while he's still using unsuitable cable.
 

rjenkinsgb

Well-Known Member
Most Helpful Member
have a CCTV microphone unit & its audio output is a RCA out (Line out) Output Level is (0-6Vpp).I want this audio to be delivered to a DVR Audio IN which is placed over 80m.Now I have wired a coaxial cable RG59 & there is so much humn/noise.
Is the audio (at the recorder or amp end) in any way at all cross-connected with the camera power or video connections - eg. do they go to the same DVR?

If there is any connection it may well just be a ground loop, where the audio screen is also acting as a power or video ground return and having other signal superimposed.

If that's the case, all it should need is a 1:1 transformer at the receiving end to break the loop.
 

crutschow

Well-Known Member
Most Helpful Member
And what does that achieve?
At audio frequencies likely nothing
I was just answering AG's comment about the transformer output being balanced, not unbalanced (single-ended).
 

Suraj143

Active Member
Is the audio (at the recorder or amp end) in any way at all cross-connected with the camera power or video connections - eg. do they go to the same DVR?

If there is any connection it may well just be a ground loop, where the audio screen is also acting as a power or video ground return and having other signal superimposed.

If that's the case, all it should need is a 1:1 transformer at the receiving end to break the loop.
YOu are right. All the devices got the same DVR unit (Cameras, MIC signal etc..)Please see my drawing.

Audio Length.JPG
 

rjenkinsgb

Well-Known Member
Most Helpful Member
A 1:1 audio transformer in line with the mic input at the recorder, should get rid of the problem.

You can buy built units cheaply on ebay, eg.

Or, the line transformer from a scrap dial-up 56K modem will work very well for general (though probably not HiFi) audio isolation - I've used those for years, until they became hard to get.
 

unclejed613

Well-Known Member
Most Helpful Member
Now I have wired a coaxial cable RG59 & there is so much humn/noise.
are both ends of the shield connected properly? a lot of 75 ohm cable has aluminum shield wires, which don't solder well (or at all). try something with copper shield wires instead.
 

audioguru

Well-Known Member
Most Helpful Member
You are using a video cable that always has video connectors attached to the foil at each end. I think your video foil shield is not connected at each end.
Some audio cables also have foil but also have a stranded copper wire running along touching the foil for connections of the shield at each end.
 

Suraj143

Active Member
Or, the line transformer from a scrap dial-up 56K modem will work very well for general (though probably not HiFi) audio isolation - I've used those for years, until they became hard to get.
Very Nice Idea. I found this transformer from a telecom PCB board. I measured its resistance from a multimeter. Will it suits for my job?
 

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