[1000mp] Bad Antenna Relay? (long)

[sdyer]

The "something happens" is called corrosion. The small current is called
"sealing current". The phone system uses it.

73,

Steve
W1SRD

> -----Original Message-----
> From: 1000mp-admin@mailman.qth.net=20
> [mailto:1000mp-admin@mailman.qth.net] On Behalf Of Tod - MN
> Sent: Friday, October 17, 2003 11:50 AM
> To: 1000mp@mailman.qth.net
> Subject: RE: [1000mp] Bad Antenna Relay? (long)
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> In some cases if relay contacts never carry current (less=20
> than 1 ma) with time "something happens" and they seem to=20
> develop a surface resistance that acts to reduce the signal=20
> transmitted through them. I have a vague recollection that by=20
> running a very small current (about 1 ma) through relay=20
> contacts when they are closed the contacts will remain 'clean'.
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> In some respects this seems to describe some of the anecdotal=20
> data points expressed on the reflector. If the contacts are=20
> mechanically burnished by switching I suppose that the=20
> surface resistance might be cleared as well.=20
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> I have absolutely no idea how we would test this idea with=20
> our 1000MP's (or variants thereof). I guess one would have to=20
> look at the circuit diagram and figure out how to run a small=20
> current through the RX contacts without losing signal. Since=20
> the error mode is not present in every MP, it may be that it=20
> is a function of the type or lot number of the relays that=20
> were used in production. It would not be the first time that=20
> a 'bad' lot of components made its way into a production=20
> line. In fact, if it was not recognized that a certain=20
> percentage of the components had attributes that caused RX=20
> problems, the specifications for the component would remain=20
> the same and the component would be used in many production=20
> runs. Since the problem occurs very, very infrequently it=20
> would not be surprising if the relay specification did not=20
> specifically deal with long term contact resistance. Further,=20
> if the cost of specifying, testing and incorporating a=20
> different relay was high enough to increase the product cost=20
> above a certain threshold, the manufacturer might choose to=20
> make no change.
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> I suppose this is the ultimate horror story from a=20
> manufacturer and user's point of view -- that the failure=20
> mode appears in only a small percentage of the production=20
> units and that simplest cure seems to be to replace a single=20
> component which resolves the problem in most cases. In a few=20
> cases one might expect that a 'not entirely good' component=20
> is used to replace the original 'not entirely good' component=20
> and a few folks are in the position of the simplest cure not=20
> being a cure for them.=20
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> My personal experience with Japanese and American=20
> manufacturers is that they (or their lawyers) are loathe to=20
> declare that there are any flaws one of their products. The=20
> may be willing to 'deal with a product that does not perform=20
> the way they think it should' as long as they do not need to=20
> publicly declare that they might need to make an engineering change.=20
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> I wonder if anyone else has the same assessment of the 'Bad=20
> Antenna Problem'?
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> Tod, K=D8TO
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