Last night I got an email from John Isabella, K1IF, stating that he’d read my blog regarding my Diamond X510, and was wondering if I knew what voltage the capacitors inside were rated at.

I confessed that I didn’t, as mine did not seem to be in need of replacing, but with a bit of math we were able to ascertain some suitable ratings, namely 300V rated 2pf capacitors. If you’re interested in the math, continue reading.

## Power Law

The Power Law states that the power dissipated in a device is inversely proportional to the squared value of the voltage across it:

P = V^{2}/R

John had informed me that he only wanted to run 100 Watts through his antenna, so we did a few calculations.

Firstly, we ascertained that the voltage across the capacitor at 100 Watts, with a SWR of 1:1, would be 70.7 Volts.

**The calculation was then performed again, assuming an SWR of 10:1, and is as follows:**

**Power = Voltage Squared / Resistance**- Power x Resistance = Voltage Squared
- 100 Watts * 500 Ohms = V^2
- 50000 = V^2
**The Square Root of 50000 = 223.61 Volts**

**Therefore, it was concluded that any capacitor rated at 300 Volts or higher should do a mighty fine job indeed. Just for reference, the value of the capacitors used is 2pf.**

*Note: I’m no expert, and I expect that in the world of High Frequency, Alternating Current Resonant Circuits with Complex Impedences (rather than purely resistive loads), Ohm’s Law and its DC **variants / derivatives don’t tell the whole story. That said, this is amateur radio, and what do we have to lose? A few burnt 2pf capacitors. That’s a gamble I’m willing to stake on Ohm’s Law. Someone please correct me if the above conclusions are misguided and/or bad advice.*

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