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Author Topic: RF damage to electronics  (Read 9912 times)

Posts: 3

« on: October 03, 2003, 12:09:51 PM »

 I'm setting up my first station.  I posted a question about adding a SWL receiver in the shack and it was brought to my attention the possibility of harming the receiver by the transceiver's output (even if the receiver is off).

 What other electonics should be kept away from a HF transceiver and feed lines for fear of damaging them?

 I've got a couple of VCR's, stereo, computer, TV (a video editing set up that shares the same location) plus all-band scanner, oscilloscope, function generator and misc. test gear all within 10-15 feet of where the rigs (a HF transceiver and VHF/UHF rig) will be located.

All this stuff will be off so I'm not worried about RF interference, but actual damage to any of them.

 The first antenna will be a dipole about 40 ft above the building.

Thanks for any thoughts,
 Joe Travis

Posts: 21764

« Reply #1 on: October 03, 2003, 01:17:04 PM »

There's no need to separate electronic equipment from your actual transmitter, since transmitters radiate very little energy from their cases -- the energy all goes up the feedline, and is (hopefully) radiated by the antenna!  I have numerous sensitive electronic devices literally sitting on top of or directly next to my amateur transmitters, in some cases sitting on top of my 1000-Watt (output power) amplifiers.  No harm at all -- the radiation isn't from the equipment, it's from the antennas.

In some cases, poorly designed transmitting equipment will *conduct* a fair amount of RF energy into the AC power mains, and might cause malfunction of other electronic devices plugged into that common mains; however, this is fairly unusual, and the malfunctions that might occur rarely cause any actual damage.  I've found, for example, that when I run 1 kW output under some conditions I can "fault" my kids' Nintendo game due to its power supply being especially sensitive to radio frequency interference.  That fault can be re-set in a second, by turning the power supply off, then back on -- so no damage occurs, but a game interruption might.

Most electronic equipment that is not designed to receive radio signals will not be damaged by strong radio frequency fields.  The most likely equipment to sustain damage is receiving equipment, since such equipment has sensitive RF stages designed to receive microvolt-level signals.  When, instead of microvolt-level signals, hundreds of volts are applied instead: Poof!  Front-end circuitry damage is pretty common.

But again, all this occurs when the receiving antenna is in relatively close proximity to the transmitting antenna and a situation exists such that hundreds of volts of RF potential arrives at the receiver's input connector.  Most amateur *transceivers* are pretty well protected against even this situation, since they contain transmitters right inside the same box as the receiver and the designers included reasonable protection.  But many *receivers* (which do not transmit) are more susceptible to damage.

Front-end protection circuits such as clamping diodes across the RX antenna terminals with a small incandescent lamp wired in series with the antenna (between antenna feedline and antenna terminal), as was previously suggested, will help a lot.  You can also buy "RF fuses," which are literally a tiny fuse installed in series with a couple of coaxial connectors and designed to "open" with the application of a few dozen milliwatts signal.  These are commonly used to protect spectrum analyzers and other sensitive lab equipment, and they're not expensive (when purchased surplus).

Overall, I wouldn't worry.  Hams have had shacks full of all sorts of equipment, while running high powered transmitters, for several decades and for the most part we don't burn anything up!

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