Topband: TX relays

[Tom W8JI]

OK Carl and Jim,

I know you want one-part-number-fits-all answers, but I do not think that is 
possible. There are tens of thousands of relays and dozens of applications.

I am afraid telling people what to do in no uncertain terms by specifying a 
part number often winds up being wrong over time as things change.

For example a few years ago a very good Struthers-Dunn high power relay 
moved to China. The internal wire that used to handle several amperes on ten 
meters now heats and melts at half that current on upper HF. The root of 
this problem is the RF specs we are concerned with as amateurs have little 
or no bearing on the 60Hz or dc relay specs, so they didn't change a thing 
for relay operation in the published low frequency or dc specs, but rendered 
it useless at radio frequencies. When a manufacturing process changes, an 
off-the-shelf relay that had good RF performance can suddenly radically 
change.

This is why manufacturers that actually use relays in large quantity, while 
some of the more "grumpy" among us might think are unfairly making money 
through sinister secrecy, are usually better sources. They do the 
consistency checking for us. Some of the relays are custom. For example, the 
RCS8V uses a custom tooled relay that has a double make double break 
contact, or form X contact. It isn't under a part number at Mouser.

73 Tom


> On Thu,10/9/2014 6:46 AM, Tom W8JI wrote:
>> Because there are many things that go into relay selection that do not 
>> show on a data sheet, I always dissect and test relays.
>
> Thanks for an excellent exposition of the issues. Now how about the other 
> half of the question -- part numbers for relays that meet the need? This 
> reflector (and the spirit of ham radio) is about SHARING information.
>
> 73, Jim K9YC
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