Topband: Relays in RX array
n4zr at contesting.com
Thu Mar 23 07:16:38 EST 2006
K9AY and KD9SV suggested the following:
Tyco/OEG OJE-SH series (sealed case, 12 volt) for spdt
Omron G2R series (sealed case, 24 volt) for dpdt
Gary specifically suggested the Tyco OMI-SH series, spdt and dpdt because he took them apart and their contacts have wiping action, plus they are sealed. They look like a good choice, and still under $2. Mouser 625, p. 1294. This is what I'm going to do.
At 09:47 AM 3/22/2006, Steve London wrote:
>> Tom wrote:
>>> I use regular 1-2 amp sealed DIP relays, and never once have had a
>>> problem despite having dozens of relays in the signal path. This is
>>> with about 20 years or so of use in some of the switches. I
>>> recently just pulled a box I built in 1983 out of service, and the
>>> relays were still fine.
>>> My suggestion would be to buy a low current sealed relay and not
>>> worry about it. If you start to have problems, then it's a simple
>>> matter to add contact bias.
>>> Where I think you will get in trouble is using higher current open
>>> frame relays, even those in plastic enclosures or covers. They are
>>> often problematic when operated without contact bias current.
>>> 73 Tom
> > Ford wrote:
>> In a Rx array, I agree. Sealed switches are the way to go. But how
>> much RF power do you dare run through a contact rated for 2amps at
>> 30v or 60v? My assumption has always been that you needed to go to a
>> relay that had at least 5-10 amp ratings to survive even modest QRO.
>> Pete didn't indicate in his regular query as to whether this was a Rx
>> array or some sort of Tx antenna. So rather than rambling on with
>> guesses, maybe Pete can describe his application.
>> When I was studying the App notes from various sources. My
>> conclusion was that a flash over was needed to burn through the gunk
>> that naturally forms on contacts exposed to air. The materials
>> involved dictated the voltage needed, but the worst case was at least
>> a 10.5v arc. The current required was typically no more than 100ma
>> rated by the manufacturer, which usually stated it on a data sheet
>> as: "Contact rating 0.10A to 30A" or whatever. Some styles and
>> materials required considerably less whetting, even though the
>> manufacturer may specify quite a bit more current to be conservative.
>> If the relay contacts were designed to do a mechanical wiping action,
>> as in meshing sideways during closure, then the benefits of running
>> DC are minimized if not eliminated. On very low current and low
>> voltage relays, this is very easy to design since the contactor arm
>> is quite flexible--low current relays can still have a long life.
>> On heavy gauge relays, the contactor arm is pretty ri gid and
>> provides little, if any, flexing. Sliding contacts under load means
>> a short life, so you rarely find wiping action on a relay designed
>> for current handling.
>Ford and Tom,
>Can you provide some examples of "good" relays you have found, say, from
>the Mouser or Digikey catalog ? Frankly, it's a little daunting to go
>through 65 pages of relays, trying to surmise which ones might be good
>for topband and then study the spec sheets.
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