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Ongoing hum

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#1
i installed new feed hardware - and feed is running - just like old software.

It still has terrible hum - and the hum IS NOT from scanner - but hum is on the line into computer.
I bought the ground loop isolator and other stuff recommended when I joined and asked this question about four months ago or so.

I live in an old apartment building (formerly a house).
Anyone have any ideas on ways to fix hum?

I have tried making feed from the other five rooms in apt. but still have that hum.
 
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#3
audio cable

This is ground loop isolator is this
Ground Loop Isolator - RadioShack.com

then the two lines go into on 1/8"-jack adapter - and a single line of that size goes into computer

I am not engineer - but hope this helps

As a news reporter have listened to scanner 24/7 for 30 years

Have old model scanner (not 800 MH) - Uniden Bearcat BC350A

But the hum is not from scanner - it emits hum into line even when not plugged into scanner,.
 

flugpop

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#4

richtidd

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#5
i installed new feed hardware - and feed is running - just like old software.

It still has terrible hum - and the hum IS NOT from scanner - but hum is on the line into computer.
I bought the ground loop isolator and other stuff recommended when I joined and asked this question about four months ago or so.

I live in an old apartment building (formerly a house).
Anyone have any ideas on ways to fix hum?

I have tried making feed from the other five rooms in apt. but still have that hum.
Here is the how to on connecting your equipment:
Setting up your Broadcasting Station - The RadioReference Wiki

Hums are caused by several rsasions including ground loops, wrong cable types or even a bad AC power Supply.
 
N

N_Jay

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#6
The issue with fixing hum is to find where it is coming from.
Often it is a ground loop[ on the audio line, but not always.
There are a few posts on chasing down the problem, do a search and see it any of the ideas help.
 
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#7
I will try this.
Just to be clear (again I am not an engineer) - I do not have RCA connections on the back of my computer - but I am presuming you mean hook the 1/8 to back of computer and then the rca cables into my ground loop isolator - and make it so it can attach to the 6-Inch Gold-Plated Premium Shielded Mono Y-Cable (with single end of it) plugged into my scanner.
 
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#8
I am afraid its the old wiring n this old house - because its the same problem in all rooms of the house (turned into apartments) - maybe its my cables but the folks at radio shack recommended the cables I am using - plus I took advise from the other posts I found in searches when I first joined.
I have tried to isolate problem to one of the cables running from scanner to computer - but all have hum. I am next going to try what flugpop suggests.
 
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N_Jay

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#9
I very much doubt it is the wiring in the house as much as poor power supply design in both the scanner and the PC leading to a ground loop.

Are the scanner and PC plugged into the same outlet?
 

Kennrth

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#10
Ground loop problems are difficult problem even for engineers to solve. You need to understand how to troubleshoot this problem. You need to start a ground isolation procedure. Using an isolation adapter plug is cheap and good place to start. Keep in mind the problem may not be your computer or your radio. The fact that you have used an isolation adapter on your audio line and it hasn’t worked. This shows that the ground loop most likely is not between your radio and computer. It may between your computer and something else.

Often over looked is a difference in ground potential between the cable ground and power ground. Unplug modem/cable/router connections from your computer. See if the problem goes away. Unplug incoming video cables to all the televisions in the house or just unplug televisions. Cable company ground may be at different potential that your local AC Grounds. Grounds are not absolute but relative. Any two grounds at different potential cause current flow usually at 60hz and end result is hum in low power sensitive lines like audio inputs. .
Observe polarity on AC Lines. Typical AC plug – round or third prong is earth ground. Wide prong is neutral, the narrow prong is AC Electric High. You need to check that your earth ground outside of house is connected. There should be a ground rod in the earth near the electrical box on the outside of your building. A ground wire ground should be clamped to the earth ground post.
You need an AC voltmeter. On your AC outlet Inside the house check voltage from third prong(earth ground) to AC neutral (long prong) should be less than 2.5 Vac ideally. Then check Earth Ground to electrical High and neutral to electrical high should be 117Vac +-10 %.
Check the bare metal part of your computer to a bare metal part of your radio. Should be same AC/DC potential. If you observe something like 60 volts you may have a phase reversal. If you are using isolation plugs observe proper plug polarity. Most appliances have large prong and a small prong to prevent the plug from being inserted in reverse. Some plugs may not be physically polarized electrically and being plugged in reverse can cause a ground loop. Some old dwelling don’t have third prong grounds or polarized ac plugs so observing ac polarity is problematic.
Try unplugging your computer speaker’s AC power, Unplug Your monitor, then unlpug your printer.
Try using a power strip plug computer and radio into power strip by themselves. Use AC isolation plug one end of power strip and plug the power strip into the wall.
Try using a wire connect bare metal part of computer case to bare metal or radio.
Disconnect any other AC lines from devices on your computer.
This is a just a start. You may need to unplug your battery charges , shavers etc .
If you have any variable light controls shut then off. Shut off fluorescent lights – starter polarity may be miswired . Try to isolate source of problem . step by step.
If there are multiple apartments in your dwelling you may need to work with others see if they are having similar problems. Temporarily unplug tv cable coming into the house to see if this solves the problem. All the tv’s in dwelling need to be isolated to see if hum goes away. There are video company cable inline ground isolators available. If this is the problem.
If you can find the source of the problem then you may come back and find a solution by posting here.

Check the Web for ground loop explanation and solutions and trouble shooting methods.
 
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#11
No the computer and scanner are plugged into separate outlets across the room from each other - tho by necessity the computer, printer, and related equipment share the same surge protecttor and outlet.
But I tried making feed from different computer (plugged in by itself in living room) and scanner in different rooms like kitchen and still have hum.
 

appalachianscanner

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#12
No the computer and scanner are plugged into separate outlets across the room from each other - tho by necessity the computer, printer, and related equipment share the same surge protecttor and outlet.
But I tried making feed from different computer (plugged in by itself in living room) and scanner in different rooms like kitchen and still have hum.
If your house wiring is of that of the older "2 wire" then most likely your computer is using the coax shield as a ground (if your antenna is grounded) and the current is flowing through the audio cable.

I solved the problem for my feed by making a dedicated, (grounded) outlet to a ground rod outside and grounding "everything" to that common ground. I attempted using a isolater in the past but found another ground path via the neutral on the scanner power cable. I know a lot of people frown upon the configuration because per NEC code my secondary ground rod should be tied (bonded) to the house's primary utility ground. However with just one outlet and nothing but the feed computer and scanner plugged in theres no easy soultion.

Everything meaning = Coax shield bonded to audio cable shield, audio cable shield to computer chassis screw, computer chassis effectively grounded by 3rd wire at outlet.

The only danger is that if lightning finds it way into the house it could choose a path via any electrical wire to this outlet then through everything connected and to ground. Therorectically since the resistance of the ground wire is less than the coax then it should follow the ground at the outlet or back (the way its supposed to) to the switchbox, since there, the neutral is bonded to the utility ground rod.

Using a isolater is the legit way to go but then you leave the insulation in a tandy made device's transformer coil as the only block in a "lightning strike finding your coax as ground" situation.

5 years ago I found out with the help of a nearby lightning strike, the expense of a scanner, motherboard, audio cable, and melted isolation transformer, thankfully the antenna only suffered superfical "melting" at the connector > mast/ground.
 
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#14
I had a crazy hum on my feed at first .. but after messing with it for awhile i figured out a quick fix...

I just simply pulled out the audio jack thats going into my pc from my scanner out just a little tiny bit.

It's a jerry rig situation mind you but it works great now.. no more hum.

So maybe try to pull the audio jack out just a little and see what happens.

Good Luck
 

richtidd

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#15
I had a crazy hum on my feed at first .. but after messing with it for awhile i figured out a quick fix...

I just simply pulled out the audio jack thats going into my pc from my scanner out just a little tiny bit.

It's a jerry rig situation mind you but it works great now.. no more hum.

So maybe try to pull the audio jack out just a little and see what happens.

Good Luck
The cause of the hum in this case is you where using the wrong cable type.

A mono plug into a stereo jack or a stereo plug into a mono jack is not the correct way to connect a radio to a computer.

The radio audio output is mini mono and a typical computer input is a stereo mini.

The mono mini is a two circuit connector & the stereo mini is a three circuit connector.

These are two different connectors and when you mix them up various audio problems are caused.

The best way is to keep the mono side mono & the stereo side stereo & use the correct cable's as shown here: Setting up your Broadcasting Station
 
Joined
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Messages
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#16
The cause of the hum in this case is you where using the wrong cable type.

A mono plug into a stereo jack or a stereo plug into a mono jack is not the correct way to connect a radio to a computer.

The radio audio output is mini mono and a typical computer input is a stereo mini.

The mono mini is a two circuit connector & the stereo mini is a three circuit connector.

These are two different connectors and when you mix them up various audio problems are caused.

The best way is to keep the mono side mono & the stereo side stereo & use the correct cable's as shown here: Setting up your Broadcasting Station

Ahh ha.. I see my issue now.

Thanks for this info..
 
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