improving 433 MHz range - Page 1
Forum section: electronics / projects

author: texane
author_rank: Regular Contributor
timestamp: January 26, 2014, 09:56:12 am
content: Hi,I recently got this module:http://blog.zakkemble.co.uk/wp-content/uploads/2012/12/modules.jpghttp://www.electrodragon.com/w/NRF905_Transceiver_433MHz-Wireless_ModuleI want to use it to transmit data between my flat and my garage, whichis 7 floors below. Thus, this is a vertical configuration. For testingpurpose, I tried this:. a module sends packets from the garage. The power gain is set to max(10 db, adjustable in software). The packet size is limited to 6 bytesCRC and automatic retransmission are disabled.. a receiving module is located in the flat. 3 different messages areprinted if the carrier is detected, data are received, and all the databytes are correct.In my flat, the carrier is not detected. 2 floors below, the carrier isdetected. 3 floors below, data are received and all correct. Thus,communication between the flat and the garage seems possible to me, butthe range needs to be improved a bit. To do so, I plan to try differentantenna designs. For instance, I found this doc, where page 14 describesthe bulding of a ground plane antenna:http://www.arrl.org/files/file/Get%20Licensed/Quickstart%20Guide%20EBOOK.pdfDo you have any advice about antenna designs that are well suited forthis kind of vertical transmission configuration ? What are the otherpoints I could improve ?Thank you for helping!

author: Psi
author_rank: Super Contributor
timestamp: January 26, 2014, 10:29:51 am
content: 1. Make sure both antennas (RX and TX) are positioned in the same orientation. If one is at 90deg from the other the range will be bad.Best range is when they're both in the same orientation.2. Linear antennas have a null zone out the top and bottom of the antenna. So if your TX and RX are right above/below each other its best to have both antennas horizontal (That way you're not trying to communicate through the null zone).If it's still not working try some better antennas, those short stubby 433mhz antennas aren't very good.You can build good 433mhz dipole antennas really easy.Get a SMA to SMA cable (assuming that's the connector on your tx/rx) and cut the coax in the middle (so you can make 2 antennas) then you can solder some up.433mhz is used a lot in the FPV community so there's lots of info on making them.Basically you want the coax coming out of the TX/RX and then solder two wires going off at 90deg and -90deg (to the coax). For 433mhz each wire should be 164.5mm long (http://www.csgnetwork.com/antennaedcalc.html)One wire solders to the coax shield, the other to the main coax conductor||164.5mm||---Coax----<transmitter or receiver>||164.5mm||

author: texane
author_rank: Regular Contributor
timestamp: January 26, 2014, 10:40:00 am
content: Thanks for your reply. The connector is actually SMA. Is there advantageof using dipole antenna in this kind of vertical transmission configuration ?

author: Psi
author_rank: Super Contributor
timestamp: January 26, 2014, 10:41:30 am
content: A dipole is better than a monopole, i dunno what is inside your current small antenna, could be either but probably monopole.I would try a horizontal dipole on the TX and RX and see what you get, it should give noticeably better range.

author: hagster
author_rank: Frequent Contributor
timestamp: January 26, 2014, 10:44:48 am
content: That ARRL antenna should work. You could add more 'ground' wires to make a bit of a cone. This would probably improve the pattern.PSI's dipole would likely also work. It doesn't include a balun like the ARRL does.The other good simple design is the sleeve dipole. This is what most WiFi antennas use. You can Google how to build it or just buy one ready made.http://uk.mouser.com/Search/m_ProductDetail.aspx?qs=K5ta8V%252bWhtZ00LNUmbKZ4g==

author: hagster
author_rank: Frequent Contributor
timestamp: January 26, 2014, 10:49:10 am
content: Of remember a dipole and monopole radiation patterns have a null end on. You might want to have the antenn horizontal to direct the pattern vertically. You could also place a reflector 1/4 wave from the antenna.

author: Psi
author_rank: Super Contributor
timestamp: January 26, 2014, 10:52:18 am
content: With those stubby 433mhz antennas the entire antenna is located really close to the RX electronics which likely increases the noise floor.A small sma extension cable to get some separation may help.Do you know what the RF output power is?

author: texane
author_rank: Regular Contributor
timestamp: January 26, 2014, 11:15:56 am
content: Thanks for your answers, they are of great help.@Psi:I do not know the radiated power, but it is less than 90mW. I wouldsay 80mW. The NRF905 states that the total current consumed bythe module when in TX mode is related to the software adjustable gainas follow:-10 dBm: 27mW-2 dBm: 42mW6 dBm: 60mW10 dBm: 90mWMy software sets the gain to 10 dBm.

author: Psi
author_rank: Super Contributor
timestamp: January 26, 2014, 11:39:49 am
content: With good antennas 80mW is plenty of power to go through a 7 story building at 433mhzI think your issue is just with the antennas.

author: NiHaoMike
author_rank: Super Contributor
timestamp: January 26, 2014, 03:03:40 pm
content: Just make a pair of directional antennas.

author: hagster
author_rank: Frequent Contributor
timestamp: January 26, 2014, 03:44:41 pm
content: Quote from: texane on January 26, 2014, 11:15:56 am10dBm(10mW) is the output power. The 90mW is the power consumption of the module. You can get more sensitivity with a slower data rate if your chip supports this.

author: texane
author_rank: Regular Contributor
timestamp: January 31, 2014, 07:00:26 am
content: Hi,I purchased this antenna which corresponds to the model described by Psi ifI am not mistaking:http://fr.mouser.com/ProductDetail/Linx-Technologies/ANT-433-MHW-SMA-L/?qs=%2fha2pyFaduizHDih74KwlXlZ4v2OdJFHHd%2f4HAnuCTScckk3zjpZ5KZM4%2frKQLyyI now receive the signal in some precise positions in the flat. This is still to weak:the carrier is detected, but data rarely arrive intact (but they do sometimes, confirmingthat the carrier is not the one of some random device nearby).I will try to build an antenna myself, as described by Psi ... but I do not believe itwill improve much.Do you have any other idea ?Thanks for your help !

author: BravoV
author_rank: Super Contributor
timestamp: January 31, 2014, 07:14:47 am
content: Too bad its way too late, last year TI had a great discount on its spectrum analyzer msp-sa430 that covers 389 – 464 MHz, official price is $250 and it was only $25 with free shipping, it was shopping frenzy ->here

author: Psi
author_rank: Super Contributor
timestamp: January 31, 2014, 07:24:33 am
content: Quote from: texane on January 31, 2014, 07:00:26 amAntennas are everything.Since you only have 10mW you could investigate high gain directional antennas but i'd make up a quick full wave dipole at each end and try that out first. Should only take an hour to solder up two of them and test them out.Full wave is 346.5mm of wire each side.And remember to have it horizontal on both transceivers.(Check if your tx/rx is actually working on 433.00mhz exactly, if its not use the calculator above to work out the exact length for your frequency)

author: hagster
author_rank: Frequent Contributor
timestamp: January 31, 2014, 09:13:39 am
content: Don't go for a Full Wave Dipole (unless it is a folded dipole). It will give you an awful impedance match and your antenna wont radiate.I did some quick simulations to demonstrate this (50ohm source). The reflection coefficient comes out as -0.64dB. What this means is that if you send 10dBm of power down the cable to the antenna 9.36dBm of it will reflect right back at you.The LINX antenna you bought looks pretty good with an SWR of about <2. The equates to a reflection coefficient of about -10dB. Meaning that for the 10dBm you transmit only 0dBm(1mW) will reflect back into the the transmitter.If you need more gain than this I recommend going for a corner reflector (This should actually improve your SWR slightly). Do a quick google and you will see lots of examples, but basically the reflector needs to be 1/4wave from the antenna(the same length as each element). For more gain than that a Yagi is a good option.