I have been operating seismic telemetry networks for years and the nature of telemetry includes an RF link, usually VHF, but often includes loaned space on someone's tower. The tower is passive, but the owner also rents space to others, such as ham repeaters, farmers c0-ops, and even AM church radios. So all the usual rules of power and signal shielding and by-passing need to be applied. But one of the sneaky-est RF to DC noise sources is the BAD ground connection. A poor ground connection will corrode and rectify any AC or RF passing through it (remember the old copper-oxide rectifiers of the '40s). The few times that we had a seemingly unsolvable interference problem, the best solution was to replace the grounding system, or at least re-do all the connections. I recommend #6 insulated (so it doesn't ground everywhere) ground cable and mechanical clamps of the same material as the ground rod and cable. (beware of aluminum). I have tried the "thermite" method of bonding a cable to a ground rod; if it doesn't work properly, it will look OK, but actually be a corrosive mess. The wavelength of AM radio is so long (200 meters at 1.5 Mhz) that aluminum foil and metallic enclosures are of little use. All our seismic telemetry is installed in PVC pipes because such is easy to seal against moisture. Regards, Sean-Thomas __________________________________________________________ Public Seismic Network Mailing List (PSN-L)
Larry Cochrane <cochrane@..............>