433.92MHz XD-FST / XD-RF modules hack with external dipole antenas? - Page 1
Forum section: electronics / projects

author: eneuro
author_rank: Super Contributor
timestamp: May 28, 2015, 11:38:25 am
content: Hello,I've in hands those cheapy XD-FST / XD-RF transmiter/receiver modules and want experiment a little bit with external antenas to get higher range in open yard while they see each other, so there are no obstacles between transmiter/receiverCalculated estimated length of needed ~1/2 dipole antena length and after removeing solder mask on ground plane oposite to antena connector soldered two wires to make something like dipole antenaHowever there is still 10mm-15mm gap between each soldered dipole antena copper wires, so unsure if it helps extend range between transmiter/receiver, while so far didn't reverse engineered those modules circuit and I'm unsure if it is possible connect external dipole antena to those modulesAnyway, I've another not hacked the same modules, so will write software to measure signal quality and can compare results using oryginal modules with ~1/4 wavelength attached to antena connector only (as shown in short description) to see if using dipole antena helps somehow, but trying to figure out if makeing classic DIY dipole external antena for this 433.92MHz (those blue/red wires in my photo) and using decent quality feed could be better than such simple soldering I've made directly to PCB?Maybe someone already reverse engineered those circuits and have schematics-it could be easier to analyze what to expect when we connect some load to data Tx/Rx pins, while there is no detailed specyfication of source/sink current, etc?

author: bookaboo
author_rank: Frequent Contributor
timestamp: May 28, 2015, 12:28:09 pm
content: Those are fine it you are doing a hobby project and they will work over a fair distance. However if you are doing a professional project or product you might want to check these with a spectrum analyser, they spew horribly all over spectrum. In fact you dont even need test gear, just tune in on a handheld radio receiver. We tested a few and decided the only thing they would be fit for was as a 433MHz band signal jammer.

author: eneuro
author_rank: Super Contributor
timestamp: May 28, 2015, 03:05:43 pm
content: Quote from: bookaboo on May 28, 2015, 12:28:09 pmPreparing to turn them ON, hopefully not city center, so probably nobody will complainHowever, made small teardown and compared transmiter with another from the same order and... looks like it is slightly different oscilator and one capacitor not populated?One PCB hasLR1 433.92(MHz I guess), but another from the same order... something likeHC R433AThose transmiter oscilators have the same frequency?Additionally two claimed 433MHz receivers PCBs has sligtly different settings calibrated with screwdriver-no laser trim?I know, in theory those recivers can be tuned to 315MHz, but why for 433MHz they are in slightly different position-due to slightly different oscilators in transmiter and someone tried match those frequencies?I wonder, if those transmiters oscilate at the same frequency 433.92MHzTrying to find transmiter oscilators datasheetsUpdate:Yep, they oscilate on the same 433.92MHz frequency, so that is fine, but 433.92MHz is closer to 434MHz, so I'd rather call them~434MHzresonatorsPDF: LR1 433.92 MHz SAW (Surface-Acoustic-Wave) resonatorPDF: R443A or 433.920 433.92MHz SAW resonatorWe'll se what happends during tests.Soldered only quater wavelength wires to second transmiter/receiver pair.Unfortunatelly, have to check also this marked blue solder joint in one of transmiters, while it is so close to neighbour plane and it looks rather like solder blob not jointBTW: It seams for the quick check, that XD-RF receiver DATA pins are connected directly to LM358 output A pin 1, so hopefully probably will be able to know some output data pin specs in receiverPDF: LM358 datasheet

author: eneuro
author_rank: Super Contributor
timestamp: June 09, 2015, 07:57:33 pm
content: OK, it is time to... launch this XD-FST 433MHz transmiter module powered at 9.6V armed with ATTiny85 MPU ~100m above ground using... box kite to... send 6wpm Morse code and we'll see what its LOS range will beNo breadboards or bloody arduinos since this thing will fly high, where decent wind speeds exists, so simply soldered this thing-as simple as it is-small hand drawn PCB with MCU 8MHz ATTiny85 DIP8 with... 4.3Vz zener diode as its Vcc and NPN transistor to toggle XD-FST input data pin powered at 9.6V using LM117 from 12V batteryI stick to those aka dipole antenas, since got decent 350m distance in similar setup with the same transmiter 433MHz @ 5V and only 1.5m above ground, so it will be interesting how far away from box kite flying ~100m above hill ground I will be able understand 6WPM Morse code

author: eneuro
author_rank: Super Contributor
timestamp: June 10, 2015, 08:40:54 pm
content: I've got today ~400m range NLOS from living room, under metal roof , througth a few trees to nearby yard hill using this cheapy 433MHz module powered at 9.6V, so probably it is time to develop repeater for this frequency, install on the roof with good antena, power everything using a few small garden PV panels and we'll see if this thing could be usable as DIY custom LoRa module, while for the moment those range results are fine at small frequencyWith additional bits data redundancy and CRC to ensure packets integrity looks like it could work quite easy even at 500m (half kilometer range), which is exactly what I need for a few projects, including weather station 300m from home.Looking for some hints how typical repeaters are implemented. Do I need two different frequencies in repeater? For LoRa probably not, since MPU can receive packet bits, verify its integrity and resend of course with some kind of protocol to identify oryginal sender. maybe it coud be good idea to encapsulate this oryginal sender message with repeater unique address, so each device could recognize repated messages easy and reject if needed, eg. due to not acceptable delay...It is interesting if with one repeater reliable 1km LOS range could be achived at low speed LoRa data exchange using those cheapy low power 433MHz modules?Anyway preparing to lanch 100m-200m above ground such 433mHz transmiter module, but not a great weather conditions today, so we'll have wait for nice windy day.Good LOS should be available if transmiter was at 150m above ground for testing, I Guess

author: benn
author_rank: Newbie
timestamp: August 13, 2016, 08:57:13 pm
content: Hi, may I ask if you have tried to use on sending data on either 2 transmitters to 1 receiver or 1 transmitter to 2 receivers?I like you to advise because I am intent to diy a doorbell project using 1/2 transmitter to 2 receivers.There is a trimmer on the receiver, have you tried adjusting that? What is the trimmer for?

author: Buriedcode
author_rank: Super Contributor
timestamp: August 13, 2016, 10:02:47 pm
content: These reciever modules aren't very selective of their centre frequency, superhets tend not to be. So you'll be fine using two transmitters to one receiver. It is best to use different addresses for different transmitters/receivers