Gents,
I've had a horrendous ground loop making its way onto the air and narrowed it down to the power supply of the cable modem. This also occurred with the power supply of the DSL modem I used to have. Isolating the modem on a non grounded line does nothing. Trouble is, I need the modem for the internet stream.
Have any of you had this problem? How did you rectify?
Thanks!
PinWiz (novice)
Welcome to the forum.
We need a bit more information on this. Since you mentioned ground loop I assume that you are using either and AM or FM transmitter and the noise is getting into that signal.
Wall warts and external power supplies are notorious for causing hum in AM and FM transmitted signal, and seem to cause more problems with FM than AM.
The reason is that the relatively strong signals from nearby transmitters get into the electronics of the supply and interact with the diodes and non-linear components in the supply and are radiated with 60 Hz modulation and this is what is heard on the receiver.
The simplest fix is to move the transmitter away from the offending device and sometimes just a few feet more separation can make a difference. For FM I have had good results by installing a clamp on choke around the power leads coming out of the power supply. You can probably get these from a consumer electronics store such as Best Buy or by mail order (Radio Shack used to have them but most stores are gone.)
Let us know if these suggestions help.
Neil
An alternative is to try a different power supply but this is difficult because many supplies are specific to the device such as your modem.
One particular power supply among very many others existing in my station creates serious hums that seem to get injected right back into the power line like carrier current.
Oddly, the resulting hum only shows up on some radios in the building and not others.
The audio circuitry directly powered by the odd-ball wallwart is perfectly clean.
Someday I want to crack it open like an egg and invent ways of filtering it properly.
I've tried an isolating power strip, not just spike protection but EMI (electromagnetic interference) filtering on those. You can sometimes find ones like the "Isobar" at Slavation Army and Goodwill stores for a few dollars, and even if they're old they still work. What it does is block the noise from anything plugged into it from going back down the line into your home power grid.
I'm having an issue here, the town council sent out a notice that my neighborhood is going to be updated to LED street lamps this spring, intersection lights and area lighting. They already have it in some places, but it's going to be widescale soon. From reading what ham radeio people are saying, it might be a nightmare, as a night listener to mediumwave AM!
Could it also be the modem itself?