Jump to content

Voltage across antenna leads


Recommended Posts



I was reinstalling all my AV gear yeaterday and when I grabbed the antenna lead to plug it into a box I got a fairly strong tingle where my arm brushed the earthed case of my Toppy.

A quick measure with the multimeter showed an AC voltage across the coax aerial plug that varied between 40 and 100 volts.

Is this normal?

Induced voltage, picked up through the coax where it is running to close to power cables.

Gadget

Link to comment
Share on other sites

Induced voltage, picked up through the coax where it is running to close to power cables.

Gadget

Thanks for the reply - I was hoping you would.

So it's not likely to cause any problems to any of the stuff its plugged into?

Should I look at rerouting the coax?

All Tuners have isolation Capacitors built in, so this should not be a problem.

Gadget

Link to comment
Share on other sites

A quick measure with the multimeter showed an AC voltage across the coax aerial plug that varied between 40 and 100 volts.

This can happen with equipement that have switch mode power supplies where the AC is rectified directly to DC e.g no isolation transformer one trick I found that may eliminate the problem is to switch the plug (0--0) around that goes into the Toppy assuming it's one of those figure 8 power cable!

cheers laurie

Link to comment
Share on other sites



This can happen with equipement that have switch mode power supplies where the AC is rectified directly to DC e.g no isolation transformer one trick I found that may eliminate the problem is to switch the plug (0--0) around that goes into the Toppy assuming it's one of those figure 8 power cable!

cheers laurie

The voltage is across the coax inner and shield, not the connector to the Toppy. It shouldn't have anything to do with the Toppy. All it did was complete the earth curcuit when I brushed my arm across its case and grabbed the unconnected coax plug.

Or are you suggesting that the Toppy's power supply is responsible for inducing the current in the aerial cable?

Link to comment
Share on other sites

Measured with high impedance digital multimeter, all volts no current (unless fault in internal circuitry) caused by RF/static supression devices between hot and cold earths in equipment power supply.

People with damp/sensitive skin eg forearm will notice this when brushing across metal cased equipment if they are earthed (presumably when hanging on to earthed antenna system lead).

Link to comment
Share on other sites

A quick measure with the multimeter showed an AC voltage across the coax aerial plug that varied between 40 and 100 volts.

This can happen with equipement that have switch mode power supplies where the AC is rectified directly to DC e.g no isolation transformer one trick I found that may eliminate the problem is to switch the plug (0--0) around that goes into the Toppy assuming it's one of those figure 8 power cable!

cheers laurie

You're dead right there, Laurie. (You knew that already - but others might not realise this ;-).

Back in Hong Kong - where all HT equipment tended to have the figure-8 plug on the equipment back - or just a flat-2-pin plug to go into the wall (like I..I) - this effect caused me major problems connecting US valve amps, UK trannie amps, Jap sources, etc .... until I bought my first digital multimeter to swap each around until I found the minimum 'leakage' (or whatever you sparkies call it). Not only did this tweaking reduce leaked voltage, but also eliminated any residual hum.

Fortunately, all Oz equipment uses the angled pins for wall sockets but still may have a figure-8 plug going into the back to cause a swap of live and neutral conductors.

Link to comment
Share on other sites



  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...
To Top