Suggestions for low cost, high gain 433MHz omni directional antenna - Page 1
Forum section: electronics / rf-microwave

author: splin
author_rank: Frequent Contributor
timestamp: January 20, 2016, 08:53:24 pm
content: By low cost I mean preferably < $10 and for 'high gain I mean better than 3 dBi. 5 or 6dBi+ would be good, 8dBi even better but unlikely at this price I guess. As this is only for experimenting, I don't want to spend $50+ on a colinear at this stage.These are cheap and claimed to be 6dBi but I'd be surprised if it is actually more than 3dBi:http://www.ebay.com/itm/1x-433MHZ-High-Gain-Antenna-SMA-Within-Needle-Rubber-Glue-Stick-6DBI-IUK-/151821134498?hash=item23593eaaa2:g:F~kAAOSwQoFWQr40Then there's this:http://www.ebay.com/itm/433MHZ-10DB-SMA-High-Gain-Antenna-Sucker-Head-Copper-Signal-99-Good-/181634223889?hash=item2a4a3e4f11:g:IqYAAOSwAL9Ui6TXI guess the term Sucker in the title refers to anyone who believes the 10dBi claim! Like Chinese battery millamp-hours and LED torch lumens, I expect Chinese dBi to be somewhat bigger than western ones!It's also over $16 although it does include 3m of feeder.Any guesses as to the real performance of the above?

author: dmills
author_rank: Super Contributor
timestamp: January 20, 2016, 10:36:13 pm
content: Does not an omni directional antenna have at most 0dBi gain by definition.....If you only want omni in one plane then that is of course a slightly different thing, a colinear is not hard to homebrew at those wavelengths (But quickly gets more then a little large).Regards, Dan.

author: HAL-42b
author_rank: Frequent Contributor
timestamp: January 21, 2016, 07:47:31 am
content: Discone and Bi-cone antennas are all the rage these days.Of course you will have to make your own.

author: Howardlong
author_rank: Super Contributor
timestamp: January 21, 2016, 08:45:20 am
content: Quote from: dmills on January 20, 2016, 10:36:13 pmNo, that's an isotropic, which also happens also to be omni.Omni directional in antenna terms refers to a single plane. A dipole or 1/4 wave are omnis. A dipole has a couple of dB gain over an isotropic.

author: nfmax
author_rank: Super Contributor
timestamp: January 21, 2016, 09:28:33 am
content: Quote from: HAL-42b on January 21, 2016, 07:47:31 amIt may not qualify as low (enough) cost, but there is this one:http://www.conrad.com/ce/en/product/190073/Aurel-650200313-433MHz-Radio-Kit. I've not tried it myself, but it is recommended herehttp://www.domoticaforum.eu/viewtopic.php?f=27&t=9630&p=76422&hilit=antenna#p76422by a guy who is a desinger & manufacturer of 433 MHz radio devices (which I have used myself, happily)

author: Unknown
author_rank: Unknown
timestamp: January 21, 2016, 03:41:38 pm
content: 10$ isn't much for a commercial product and a few db won't make that big a difference (assuming the cheapo antenna is actually resonant where it is supposed to be). I've had great success in the past with J-pole based designs:https://en.wikipedia.org/wiki/J-pole_antennaThey are easy to make and tune and work well. You can bend up a bit of wire and have one working in half an hour.

author: Howardlong
author_rank: Super Contributor
timestamp: January 21, 2016, 04:42:59 pm
content: Quote from: splin on January 20, 2016, 08:53:24 pmNeither will have any more gain than a 1/4 wave I'm afraid, which over a reasonable ground plane is not far off a dipole, so about 2dBi.For gain you need some means of squeezing the lobes in which is typically done for omnis by using phased dipoles on top of each other, and your average white stick colinear achieves this by end feeding those dipoles on top of each other. You get a better pattern and gain from fewer radiators by spacing them a bit further apart and feeding them separately in phase with a power splitter, but this makes for a more complex and expensive arrangement. The in-phase interference from the stacked radiators orthogonal to the antenna is additive and flattens the radiation pattern.