[TowerTalk] 4 square switching relays

jimlux jimlux at earthlink.net
Fri Mar 27 08:40:57 PDT 2009

Pete Michaelis - N8TR wrote:
> At 09:34 AM 3/27/2009, jimlux wrote:
>> Pete's right.. I should have said "some" makers..
>> But I did search and the only thing I turned up is the following post
>> (from Pete).......
> I found in my archives the following post from W2VJN:

Excellent.. I guess the TT archive search doesn't go back that far..

>  > >
>  > > Does anyone have wisdom to share on selecting relays for
>  > home-brew legal
>  > > limit remote antenna switches?  In particular, can anyone
>  > explain to me what
>  > > an RF Relay is, as opposed to the common Power Relay?
>  > >
>  > > Is there any reason that I can't use an off-the-shelf 30 amp
>  > power relay to
>  > > switch RF?
>  > >
>  > > Thanks!
>  > >
>  > >             ***dan, N6BZA
> The relays which we use in the Top Ten Devices boxes are 10 amp,
> sealed power relays.  They are very small and have very low
> inductance.  The contacts are connected to the base pins with
> wide conductors.  I have run many power tests on these relays
> and the pc boards they are mounted on with temperature monitors
> and they will take full amateur power (+) to over 30 MHz.  We
> rate our boxes conservatively at 1.5 KW.  The part number is
> JW1FSN-DC12V.  They come with several different brand names on
> them.  Similar relays are being used by other manufactures of
> amateur boxes and they rate them variously at 3 KW and 5 KW.
> George, W2VJN

So "many power tests"..  and that's sort of typical for ham products, 
which is just fine.  However, I wouldn't put that in the "extensive and 
complete testing" category, nor would I call that "engineering"... 
Basically, it's empirical cut and try craftsmanship, which works quite 
nicely for a point design, but doesn't give you much information on "how 
to select a relay for a new design" (which was the original question in 
the thread); it's more of a "I tried this and it worked in my application"

In a low volume cost sensitive market like hams, empirical design is 
what I would use, too.  Most hams aren't going to pay what it would cost 
to have a real test campaign with life predictions and guaranteed RF 
performance over all conditions.  They (and I) are perfectly happy going 
for less expensive, and potentially having to go shake the dust out of 
the relay box every few years, clean the contacts, periodically replace 
things, or whatever.

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