a small directional antenna or another solution  - Page 1
Forum section: electronics / rf-microwave

author: mrmrzamany
author_rank: Newbie
timestamp: July 22, 2016, 01:37:01 pm
content: Hello,I really spent too much time on the internet searching for a small directional antenna (not more than 15 cm) and i faild to find one. According to the websites that i visited all what i found is big antennae and is not suitable to what i wantmy project is fly a small drone, the drone gonna have 4 different RF receivers from these (http://www.hoperf.com/upload/rf/RFM26W.pdf) the drone will fly to search for the transmitter ( this can be done by knowing the RSSI value; for example if the value is higher on the right the drone will turn to right) so in order to know the signal direction i chose to have a directional antenna but it seems like there is no small directional antenna, what do you think, do you have any suggestion to know the direction of the signal ?? did you see a small directional antenna before?? will the directional antenna work for this transicever?the transceiver frequency is 433 MHznote that the system will work in a room that has an area of (5 m x 4 m)thank you

author: Kilrah
author_rank: Unknown
timestamp: July 22, 2016, 02:00:46 pm
content: A sufficiently directional 433MHz antenna will be way bigger than what you want, no doubt. That positioning method also pretty certainly won't work in a tiny environment like this either.You should probably look at visual or ultrasonic methods.

author: PA0PBZ
author_rank: Super Contributor
timestamp: July 22, 2016, 02:32:41 pm
content: Direction finding with small antennas can be done by using doppler.Seehttp://members.chello.nl/~w.hofman/pa8w/dopplerRDF.htmand google for theory and practice.

author: mrmrzamany
author_rank: Newbie
timestamp: July 22, 2016, 02:44:46 pm
content: Quote from: Kilrah on July 22, 2016, 02:00:46 pmfirst I want to thank you for replaying to my post, and then Can you specify a method for me I want a simple method and I don't want to make the project complicated

author: mrmrzamany
author_rank: Newbie
timestamp: July 22, 2016, 02:46:10 pm
content: Quote from: PA0PBZ on July 22, 2016, 02:32:41 pmHello,thank you for replyingis the doppler the easiest method ?? I want the idea to be simple, If there is a solution to know the location of the transmitter inside a room by flying a drone this will be great

author: PA0PBZ
author_rank: Super Contributor
timestamp: July 22, 2016, 03:01:51 pm
content: If you are not hooked to the idea of using RF then yes, there should be simpler solutions.If your transmitter is on the floor and your drone is flying I'd try to send IR from the transmitter and put a 4 quadrant detector on the bottom of the drone.That way you can detect in what direction you have to go and when the 4 quadrants are all detecting the same level you are right on top of your target

author: Melt-O-Tronic
author_rank: Frequent Contributor
timestamp: July 22, 2016, 03:04:50 pm
content: Pseudo-doppler at 433 MHz will be way too bulky & heavy for a small drone. You'll need at least 4 quarter-wave antennas (roughly 18 cm) spaced about 1/3rd wavelength apart (~23 cm). Then there's the receiver and RDF circuit."In a room" changes this from a moderately complicated project to a very complicated one. Signal reflections mean multiple copies of the wave front arriving at the array from different directions and at different phases.I wish I had a better answer, but I don't think that a 433 MHz transmitter is an appropriate beacon for this application. A coded IR beacon would probably be much easier.

author: mrmrzamany
author_rank: Newbie
timestamp: July 22, 2016, 03:10:31 pm
content: Quote from: PA0PBZ on July 22, 2016, 03:01:51 pmDo you have a link/product/paper that I can read ? I don't have a big knowledge about IR , and I don't know what quadrant detector is

author: mrmrzamany
author_rank: Newbie
timestamp: July 22, 2016, 03:12:04 pm
content: Quote from: Melt-O-Tronic on July 22, 2016, 03:04:50 pmThank you !I don't know what is coded IR beacon, can you provide me with a link/paper/product that I can read from

author: Kilrah
author_rank: Unknown
timestamp: July 22, 2016, 03:20:07 pm
content: Some ideas/alternatives...https://www.eevblog.com/forum/projects/new-'indoor-gps'-advertised/msg977285/#msg977285(ultrasonic, last post has some IR stuff)https://www.eevblog.com/forum/crowd-funded-projects/own-kickstarter-subpos-ranger-indoor-positioning-system/(RF, timing based)

author: GandalfDerGraue
author_rank: Contributor
timestamp: July 22, 2016, 08:31:32 pm
content: Hmm, what kind of RF source do you want to detect/ locate? Is it weak RF source (I'd say well below 1mW?), like an oscillator or is it using RF amp for high output? (>1mW ++)Maybe use kind of magnetic loop antenna? In that case I'd expect a mag-loop being well under 15cm diameter, more of an LC-circuit where the "L" is something like 3-5 turns of ~1-2cm diameter, resonant by some trimmer-C ? The coil would point to the RF source if RF level is at maximum and I'd expect it being well proportional to the distance to the RF source. Just some idea, I never did really investigate that closer, but for the "doppler" thing you do need some audio card of at least some laptop or something like that, so that's probably no option for you, right?