eepete
Platinum Member
So a better or different brand of GFI is something to try. You can't really tell anything about the devices RFI (Radio Frequency Interference) immunity, so it's a hit and miss. At least the cost is less than what it cost to play with hydraulics.
As far as corrective actions go, one thing I did not see in the post is whether or not anything was plugged into the GFI. This might be a clue because there are three ways the RFI can get into the device:
1) RF hits wires on device plugged into the RFI
2) RF hits wires in the house connected to the RFI
3) RF is directly getting into the device's circuits
For all three possibilities, a new device (different brand probably) is the easiest thing to try.
So whether or not something is plugged in affects (1). Solution is to put ferrite beads on the cord of what is plugged into the outlet close to the outlet.
If the "way in" is (2), then put ferrite beads on the AC wires where they come into the device.
If the "way in" for the RFI is (3), you could try changing out the plastic box the GFI outlet is in for a metal one and try a metal plate on it. A metal plate outlet cover might also be a quick and cheap thing to try.
Radio Shack (Americas Technology Store, which explains a lot about the state of the country but that's a different topic) may still sell clip on ferrite beads. If not, I can post other sources. This is a somewhat intensive medium expensive trial and error process with no guarantee of success. You'll need to clamp the bead or barrel around all three wires, might need more than one due to inside diameter of the bead issues.
This assumes you have to use the radio close to the outlet, and have to have a GFI outlet.
VHF portable radios (up to about 150 MHz) can be set to output up to 7 watts out. 800 MHz portable radios are usually set to less than 1.5 watts out. For mobiles, VHF runs 25 to 100W, and 800 MHz run 5 to 8 watts. As frequency get higher, the human body shows more heating effect. There is still much debate about how much effect RF non ionizing radiation has on humans. I believe cell phones max out in the .3 to .6 watt range, not as sure on that one. At higher frequencies, it takes shorter length pieces of wire to pick up the signal. So electronic circuits that were unaffected by 150 MHz radios get interference they never saw before from 800 MHz radios. Since the wavelength of 800 MHz signals is much smaller than 150 MHz, the signal can also "sneak in" to devices through smaller holes. If you've noticed that AM radio in a truck fades when you drive under a bridge but FM doesn't it's because of the wavelength. AM radio (at 1 MHz or so) has a very long wavelength and the "hole" that is under the bridge is too small to have the signal pass through. FM radio at about 100 MHz passes through no problem. A hole in a device that is around 1.5 inches is enough to let the 800 MHz signal get in. For 150 MHz, that hole has to be about 8 inches. Think of these sizes as they relate to outlet and wiring boxes and you can see that the introduction of 800 MHz radios starts to expose many devices to RFI that they have never seen before.
Hope this background makes sense. I also hope the geeks in the crowd will cut me some slack here, I've made a lot of assumptions and generalizations in order to present a first order view of the situation.
Pete
As far as corrective actions go, one thing I did not see in the post is whether or not anything was plugged into the GFI. This might be a clue because there are three ways the RFI can get into the device:
1) RF hits wires on device plugged into the RFI
2) RF hits wires in the house connected to the RFI
3) RF is directly getting into the device's circuits
For all three possibilities, a new device (different brand probably) is the easiest thing to try.
So whether or not something is plugged in affects (1). Solution is to put ferrite beads on the cord of what is plugged into the outlet close to the outlet.
If the "way in" is (2), then put ferrite beads on the AC wires where they come into the device.
If the "way in" for the RFI is (3), you could try changing out the plastic box the GFI outlet is in for a metal one and try a metal plate on it. A metal plate outlet cover might also be a quick and cheap thing to try.
Radio Shack (Americas Technology Store, which explains a lot about the state of the country but that's a different topic) may still sell clip on ferrite beads. If not, I can post other sources. This is a somewhat intensive medium expensive trial and error process with no guarantee of success. You'll need to clamp the bead or barrel around all three wires, might need more than one due to inside diameter of the bead issues.
This assumes you have to use the radio close to the outlet, and have to have a GFI outlet.
VHF portable radios (up to about 150 MHz) can be set to output up to 7 watts out. 800 MHz portable radios are usually set to less than 1.5 watts out. For mobiles, VHF runs 25 to 100W, and 800 MHz run 5 to 8 watts. As frequency get higher, the human body shows more heating effect. There is still much debate about how much effect RF non ionizing radiation has on humans. I believe cell phones max out in the .3 to .6 watt range, not as sure on that one. At higher frequencies, it takes shorter length pieces of wire to pick up the signal. So electronic circuits that were unaffected by 150 MHz radios get interference they never saw before from 800 MHz radios. Since the wavelength of 800 MHz signals is much smaller than 150 MHz, the signal can also "sneak in" to devices through smaller holes. If you've noticed that AM radio in a truck fades when you drive under a bridge but FM doesn't it's because of the wavelength. AM radio (at 1 MHz or so) has a very long wavelength and the "hole" that is under the bridge is too small to have the signal pass through. FM radio at about 100 MHz passes through no problem. A hole in a device that is around 1.5 inches is enough to let the 800 MHz signal get in. For 150 MHz, that hole has to be about 8 inches. Think of these sizes as they relate to outlet and wiring boxes and you can see that the introduction of 800 MHz radios starts to expose many devices to RFI that they have never seen before.
Hope this background makes sense. I also hope the geeks in the crowd will cut me some slack here, I've made a lot of assumptions and generalizations in order to present a first order view of the situation.
Pete
