I'm curious about your comment regarding Kovar being used as relay contacts. The main (and only, as far as I know) claim to fame for Kovar (ignoring high temperature turbine blades etc.) is that it has a Tc that matches alumina and some glasses, so it is used as a backing for thin and thick film ceramic hybrids, and as leads for small diodes etc. that are fused into glass.
There would seem to be no reason why relay contacts need to be made from a ferromagnetic material. After all they are simply passing current, so whether they are ferromagnetic or not would seem to be irrelevant (although Kovar's lousy conductivity certainly would matter!). Kovar's natural oxide layer would also seem to be a problem at low signal levels. Typically, relay contacts are made of silver (with various surface treatments), or in the case of very low current, gold plated silver (or gold alone). In reed relays, other contact materials may be used, but oxidation is impossible because reed relay contacts are sealed in glass, in either a vacuum, or an inert gas. So the whole thing is still a mystery. The minimum -20dB signal level that is claimed to be needed for the relay in question still sounds like a red herring. I have used various lower frequency RF 50 Ohm relays (at 500 MHz or so), and there was no problem with passing signals at -80dB or lower. Bob Wilson TIR Systems Ltd. Vancouver. -----Original Message----- From: Christman, Timothy (STP) [mailto:[email protected]] Sent: May 24, 2002 1:53 PM To: Robert Wilson; [email protected] Subject: RE: Coaxial Switches - use with spectrum analyzer and gear? This may not be the effect being referred to, but... Relays require a ferromagnetic alloy, such as Kovar for the contacts. The leads leading to the connector are more likely beryllium copper or some similar material. The weld or joint between them forms a thermoelectrically active junction, and an associated error potential. Ideally, the two contacts form two sets of junctions that are opposite in polarity. In reality, they are seldom identically constructed, and if there's a temperature gradient across the part the error is magnified. Perhaps this was an effort to stress that the signal amplitude should be in excess of the thermoelectric offsets. Another possibility -- Many small form-factor relays are the reed type, so wiping action across the contacts forms a conduction path. There may be a minute oxide layer there or elsewhere in the system which will create the non-linear behavior described. Point contact rectification and dielectric breakdown become possibilities. Probably not pertinent, but interesting. Timothy J. Christman Test Engineer Tel 651.582.3141 Fax 651.582.7599 [email protected] Guidant Corporation 4100 Hamline Ave. N. St. Paul, MN 55112 USA www.guidant.com -----Original Message----- From: Robert Wilson [mailto:[email protected]] Sent: Thursday, May 23, 2002 6:32 PM To: [email protected] Subject: RE: Coaxial Switches - use with spectrum analyzer and gear? As it is stated, below -20dB, nothing at all comes through the switch. Then once you reach that level, output signal level suddenly begins increasing from zero. That obviously makes no sense and is probably only a result of an engineering spec being lost in translation when Marketing created the Data Sheet. Losses are not an offset that must be overcome before any output is generated, but simply as Ken mentioned, a proportion of input power. Bob Wilson TIR Systems Ltd. Vancouver. -----Original Message----- From: [email protected] [mailto:[email protected]] Sent: May 23, 2002 1:37 PM To: [email protected] Subject: RE: Coaxial Switches - use with spectrum analyzer and gear? That information is from an application document found on the Dow Key web site. I can't say that I fully understand it myself. Richard Woods Sensormatic Electronics Tyco International -----Original Message----- From: Ken Javor [mailto:[email protected]] Sent: Thursday, May 23, 2002 3:59 PM To: [email protected]; [email protected] Subject: Re: Coaxial Switches - use with spectrum analyzer and gear? I don't understand the snipped statement below. Isn't the loss just a fraction of the power flowing through the switch? ---------- >From: [email protected] >To: [email protected] >Subject: RE: Coaxial Switches - use with spectrum analyzer and gear? >Date: Thu, May 23, 2002, 12:22 PM > > A minimum power of about -20dbm must be used to overcome the > losses in the switch. ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [email protected] Dave Heald: [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on "browse" and then "emc-pstc mailing list" ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [email protected] Dave Heald: [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on "browse" and then "emc-pstc mailing list" ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [email protected] Dave Heald: [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on "browse" and then "emc-pstc mailing list"
