Jim and Roger, thank you very much for reply, I knew it was not so simple.
> Date: Fri, 18 Jul 2008 06:46:42 -0700
> From: email@example.com
> To: firstname.lastname@example.org; email@example.com
> Subject: Re: [TowerTalk] TX RELAYS
> David J. Sourdis wrote:
> > Hello All,
> > I need advice on relays. What are the minimum parameters should I look for?
> > http://www.findernet.com/en/products/profiles.php?serie=46&lang=en
> > Would the relay in this link work to withstand 1500W or say 2000W to have a
> > safety margin?
> > I have calculated the following, please correct me if wrong.
> > I= Square root ( Power/R) = SQRT(2000W/50 ohm) = 6,3 A. Based on this, 10A
> > rating would stand up to 5KW = 50 ohm x 10A^2.
> > Voltage would be V= I x R = 6,3A x 50 ohm = 315 Volts.
> > I know it is not the same the ratings for 50 - 60 Hz as it is for 28 MHz...
> Bear in mind also that you've calculated for the proverbial (and
> non-existent) "well matched system".
> The typical rule of thumb is to require design to 10dB over or test to
> 6dB over the expected maximum power. (because that's the worst case
> with a worst case mismatch)
> That is, if you calculate 315V, you'd want a relay tested to 630V, or
> designed to about 1kV breakdown. Ditto for current.
> So, the 10A relay isn't going to hack it.
> Also, keep in mind that for voltage it's "peak voltage" that counts, not
> If your system has any sort of resonant components in it, you need even
> more design margin, depending on the Q of the resonance. A Q of 10
> implies that 10 times as much energy is stored in the system as is
> passing through, that is, sqrt(10) (about 3) times the voltage and current.
> (why those contacts on inductor band switches might get burned, eh?)
> (In microwave high power breakdown testing, we use a technique called a
> resonant ring to get high average powers when we don't have a source
> that can just crank out as much as needed.
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