As a quick off-the-top-of-my-head calculation, I take 300,000,000, the speed of light in meters/second (approximate), divide by cycles per second, you get wavelength in meters. In this case, parent calculates a quarter wavelength. A full wavelength is about 5.9cm. It’s easy to get off by an order magnitude in your head, but if through sheer repetition you know 28Mhz is about 10m, you’ll know you’re off if your 30Mhz calculation gives you 0.98m. And you can do the math from there to figure out that 14Mhz is about 20m, etc. Do it enough and you can mentally move some decimal points in your head to get a pretty good approximation for about any frequency. I learned it at some point fiddling with amateur radio, but here’s a page that I think explains it well: http://www.digitalairwireless.com/wireless-blog/t-5ghz/calcu...

300 000 000 m/s

Yeesh, it’s right there in the article I linked, innit? Fixed, thanks.

It has to do with quarter wavelength features making good antennas.

I would say that you want to be less than 1/10 of the wavelength to minimize the effect though.

Antennas are usually built to 1/2 or 1/4th the size of the wavelength. I'd imagine that's why - but am curious myself if it is something else. It's the only 1/4th fraction that comes to mind.

I don't know if there's a specific name for it, but a quarter wavelength shows up as an important feature size in a bunch of RF (and acoustic) formulas. The exact physical reasons seem to vary by context.

I would also like to know this. I don't know if there's a save function in h.news or not so leaving a comment

If you click through to the comment, you can "favorite" it and then it shows up in https://news.ycombinator.com/favorites?id=dukes_haven&commen... which you can also find on your profile page under "favorite comments".

Wow. I'm one of today's lucky 10,000. Thanks!

It will dissapear more slowly here: http://handlr.sapico.me/Home/ByTag?Name=diy :p ( unfinished webapp)