On 5/25/2011 2:01 PM, FRED TOWNSEND wrote: > Pacemakers are a lot like avionics relative to ham > radio. The working spectrums for pacemakers, avionics, and ham radios are > widely > separated by both frequency and function. The probability of their mutual > interaction is very small. Unfortunately the penalty for even small errors in > pacemakers or avionics is very high. The testing is extensive but there is no > way one can conceive of all error modes therefore testing will always be > incomplete.
Well said. One of the most difficult hazards to pacemakers is a cell phone used by the person wearing pacemaker -- worst case, it's a 1 watt PEP AM UHF, transmitter within inches of the pacemaker. It's difficult because it's AM, because of the proximity, and also because the wavelengths are short enough that relatively small conductors inside pacemaker can be effective receiving antennas, and relatively small signal loops can provide significant magnetic coupling of near field signals.Strong magnetic fields, like those generated by big transformers and motors, are another serious hazard. Those hazards, and the potentially tragic results of failure, forced pacemaker mfrs to seriously get religion about design and mfg that avoids RFI. Those hazards have all been around for at least a decade, long enough that any modern pacemaker from a serious mfr is almost certain to have excellent immunity to RFI and magnetic fields. If you want to be extra cautious, simply be careful in your home and shack to avoid putting strong magnetic and RF fields around the area where your pacemaker is going to live. That includes placing TX antennas as far away as practical, using effective common mode chokes on transmission lines, using power supplies with transformers that minimize leakage flux, and making sure that there are no wiring errors in your mains power (that is, AC) that set up strong magnetic fields. These wiring errors are discussed in my tutorial about Power and Grounding for Audio and Video Systems, and in the power point about Ham Interfacing. Detailed advice on coax chokes is part of the RFI tutorial for hams. http:audiosystemsgroup.com/publish.htm The RFI tutorial also includes suggestions for clearing the problems with security systems, which are well known RFI dogs. Two common fixes are using twisted pair for all interconnect wiring (CAT5, for example) and using a small capacitor across that wiring at both ends wiring between the sensor and the main unit. In some situations, a ferrite common mode choke may help. 73, Jim Brown K9YC ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
