Directional antenna design? - Page 1
Forum section: electronics / projects

author: Things
author_rank: Regular Contributor
timestamp: January 05, 2013, 01:25:52 pm
content: Hey guys,I'm looking at DIY'ing a directional lightning sensor, but need a few pointers on possible antenna designs to achieve the best results.I'm basically looking for an antenna design optimized for around 500Khz, and is also directional. There is a commercial lightning detector available, and the antenna unit is contained in this little box!It's stated range is around 500km, with pretty nice position accuracy!So my question here is, does anyone know what kind of antenna design is being used in that box to detect the ~500Khz impulse from lightning, directionally?Cheers,Dan

author: NiHaoMike
author_rank: Super Contributor
timestamp: January 05, 2013, 02:12:55 pm
content: Phased array.

author: lgbeno
author_rank: Frequent Contributor
timestamp: January 05, 2013, 03:41:49 pm
content: Could be as simple as a pcb patch antenna in there. I assume that a lightning detector is simply looking for some bust of broadband radiation, so the purpose of 500khz is simply that this is a otherwise quiet part of the spectrum. There are some really simple types of antennas that could get you there. Dipoles have two nulls so they are a little directional but that could be supplemented with some corner reflector similar to the typical UHF tv antenna. 500khz wavelength is pretty long so those types of antennas will be very large.You should just take apart tear down that you are holding, if it is a pcb, measure the geometry and make your own that way. Check out minicar units.com too for some components that you could use to test things out.

author: Things
author_rank: Regular Contributor
timestamp: January 05, 2013, 03:52:13 pm
content: Wish I could do a tear down, but that pic isn't mine, and that little box alone costs over $150! I'd hate to buy one and find out it's a bit of wire wrapped in a coil.People seem to be using antennas like this for detecting, is it possible for this design to be scaled down enough to fit into that small box, while still having enough gain for a >100km detection range? That little box unit claims 500km, which seems insane for such a tiny antenna!

author: lgbeno
author_rank: Frequent Contributor
timestamp: January 05, 2013, 03:52:29 pm
content: Grr, minicircuits.com. BTW range at low freq is really good because channel loss is proportional to freq. high freq attenuated more. Also more 500khz waves will reflect off the ionosphere.There probably some HAMs on the forum that could help more than me.

author: lgbeno
author_rank: Frequent Contributor
timestamp: January 05, 2013, 03:58:20 pm
content: I completely agree, antennas usually look in expensive at face value, the problem is that they need really precise manufacturing Nd design time to gettuned just right.I think the trade off with smaller antennas is the overall antenna gain, you could make up some range with a very sensitive receiver. That's probably the whole picture on the range of your reference system is that the combo of antenna + receiver yields a range of 500m.What's the application driving the need for directional?

author: JackOfVA
author_rank: Unknown
timestamp: January 05, 2013, 04:39:51 pm
content: Probably a pair of ferrite rod loop antennas at 90 degrees to each other.From this configuration, with a 90 degree phase shift network, one can synthesize a null steerable over 360 degrees. However there still remains a 180 degree ambiguity. That is normally resolved with a separate sense antenna.This technology goes back to pre-WW I, where it was done mechanically with an inductive goniometer.

author: Zad
author_rank: Super Contributor
timestamp: January 05, 2013, 05:13:38 pm
content: Yes, it will be 2 or possibly 3 coils of wire wrapped around ferrite.

author: Thor-Arne
author_rank: Unknown
timestamp: January 05, 2013, 09:32:15 pm
content: Quote from: Things on January 05, 2013, 03:52:13 pmThat looks like a couple ofMW Loop antennas.