Cautionary tale 433/4 MHz licence exempt rf modules

[gaz57bag]

My wife has a shiny new Nissan Note with the now standard central locking, much to her dismay she could not get the car open and then it refused to start (key-less ignition too), well it just so happens I'm developing a 433 MHz telemetry transmitter using RTTY with one of those poky-wee 10 mW license exempt rf modules, what harm can it do there is hardly enough rf output to go through a wet hanky, wrong!
These modules have about the same radiated power as a radio car key with the benefit of a better aerial, closer investigation revealed that not only was it messing up our cars lock it was wandering all over the electronics on my work bench and was actually being envelope detected by my PC's sound card and the RTTY program on my PC was able to decode it. In my misspent youth I was a licensed ham and was accustomed to making sure rf signals stayed where they should be but this one had me going I had an rf signal generator with more oomf than this little module. The bottom line is be careful if you breadboard one of these wee beasts if the rf gets into you're picaxe odd things you can't account for may happen some rf bypassing is probably a good idea

 

[techElder]

You've obscured your location for some reason.

 

[gaz57bag]

My wife has a shiny new Nissan Note with the now standard central locking, much to her dismay she could not get the car open and then it refused to start (key-less ignition too), well it just so happens I'm developing a 433 MHz telemetry transmitter using RTTY with one of those poky-wee 10 mW license exempt rf modules, what harm can it do there is hardly enough rf output to go through a wet hanky, wrong!
These modules have about the same radiated power as a radio car key with the benefit of a better aerial, closer investigation revealed that not only was it messing up our cars lock it was wandering all over the electronics on my work bench and was actually being envelope detected by my PC's sound card and the RTTY program on my PC was able to decode it. In my misspent youth I was a licensed ham and was accustomed to making sure rf signals stayed where they should be but this one had me going I had an rf signal generator with more oomf than this little module. The bottom line is be careful if you breadboard one of these wee beasts if the rf gets into you're picaxe odd things you can't account for may happen some rf bypassing is probably a good idea

I have avoided the forum for some time as I have a gift for howlers therefor have been slowly feeling my way around, I have been careful how much information I provide ever since a magazine forum I joined got hacked and all of my personal details were possibly stolen. By the way during my we rf blunder my transmitter was in the house about 30 feet from the car the missus was standing about three feet from the car and at one point actually sitting inside! Needless to say I will be using good coax, rf chokes and plenty of bypass capacitors. Incidentally the pic processors knock out quite strong harmonics right into the VHF bands I also have a talking alarm clock is suspect uses PWM it breaks through on my bedside radio with surprisingly good fidelity!

 

[techElder]

I was trying to ascertain if your Nissan should have expected external transmissions around 433MHz, and in the UK it certainly should expect plenty!

 

[manuka]

Gaz57bag: For the benefit of others can you please specify your 433 MHz module and RTTY type being used. Did the problem go away when you turned off the errant TX ?

I don't have a handy Nissan Leaf to check, but over the decades (& with all manner of modulation schemes -even Hellschreiber) I've never had any such woes with numerous 1-25 mW 433 MHz TX modules (OOK/ASK, FSK, GFSK, & recently LoRa&#8482. Stan. (ZL2APS since 1967)

 

[AllyCat]

Hi,

And I wouldn't take that Nissan anywhere near Indianna at Halloween.

Cheers, Alan.

 

[srnet]

433Mhz modules transmitting around the common frequencies for car key fobs, will indeed interfere with central locking.

In my case I was 'testing' over the park and could not get back in my car, the test trasnmitter was still powered on and in my pocket.

But to interfere with the central locking when your 10 times further away than the person holding the fob, does suggest a problem somewhere, maybe the 433Mhz is putting out a lot more than 10mW ?

 

[manuka]

maybe the 433Mhz is putting out a lot more than 10mW

My thoughts as well! Either that or some local radio ham was operating on this ham legal UHF 70cm band with Watts -10s of Watts of power. Such levels are quite legal for hams, some of whom still smart at being forced to share the tiny 433.92 MHz ISM spectrum slice of their once exclusive 420/430-450MHz band.

FWIW Google reveals the otherwise esteemed Nissan Leaf has had all manner of starting e-woes ...

 

[gaz57bag]

I was originally designing a telemetry transmitter for high altitude ballooning but got cold feet (too much to go wrong) and decided to to convert it to a weather station at the bottom of my garden using solar power, 50 baud ASCII using AM or FM audio frequency shift keying was OK it's only sixty feet or so to the bottom of my garden and is simple I could have used other data modes but I had already fleshed out the bulk of the software and I understood it's limitations.
I have a nice RF module from RF Solutions but kept it for Sunday best and bought a couple of pairs if cheapie modules from a radio rally the transmit module is an AFSK unit using a saw filter on 433.92 I have checked the out put and the current drain the module only draws 3.5 mA when running at 3 V the efficiency is probably not that great I did check the output with a dummy load and diode probe which seems to confirm a ball park figure of about 10 mW. The rf module looks like a FS1000A unit and was only intended for testing purposes as I would prefer to use something with a slightly better pedigree for the finished product.
I have to admit it does not say much for Nissan if the system has difficulty with a bit of de sensing, I remember we had a 70cm ham repeater on the works roof some owners were getting locked out of their cars form 200 yards away.
I'm accustomed to working with VHF signals I used to modify ex PMR gear for the HAM bands I only posted this because there are possibly others doing similar, breadboards spaghetti wiring long power supply and download cables scope probes ditto, probably are not a good mix. I may have just been unlucky but since I tidied up the test bed the thing is behaving better, I think the car is going back to the dealers.

 

[Goeytex]

What do you expect with a 50c transmitter?

 

[srnet]

I was originally designing a telemetry transmitter for high altitude ballooning but got cold feet

You need to use LoRa modules, such as Hope RFM98 and Dorji DRF1278F.

I am just about to try out a new LoRa tracker for Pico balloons. Its for 'another' platform, but I flew a PICAXE one in January, the first to use LoRa for tracking. Circa 270km @ 1000bps @ 10mW. Weight with battery, around 18g.

AFSK RTTY wont go very far, FSK RTTY will but it drifts around a lot so needs constant manual attention to tuning, on most modules.

I can forsee that whilst FSK RTTY was king for HAB tracking in the UK in the past, LoRa is going to take over, its just simpler and cheaper to receive, can handle low or high data rates and goes further. And if you insist on retro the LoRa modules can do AFSK and FSK RTTY too.

 

[gaz57bag]

You need to use LoRa modules, such as Hope RFM98 and Dorji DRF1278F.

I am just about to try out a new LoRa tracker for Pico balloons. Its for 'another' platform, but I flew a PICAXE one in January, the first to use LoRa for tracking. Circa 270km @ 1000bps @ 10mW. Weight with battery, around 18g.

AFSK RTTY wont go very far, FSK RTTY will but it drifts around a lot so needs constant manual attention to tuning, on most modules.

I can forsee that whilst FSK RTTY was king for HAB tracking in the UK in the past, LoRa is going to take over, its just simpler and cheaper to receive, can handle low or high data rates and goes further. And if you insist on retro the LoRa modules can do AFSK and FSK RTTY too.

I agree with you entirely about the LoRa units and I always though that too much emphasis was placed on SSB especially for phone work I have good hearing a musical ear and despite all of that if it was a choice between noisy FM and SSB the noisy FM was always easier for me to copy,however this project only has to go the bottom of the garden (rare DX indeed) and I really wanted to see what I could squeeze out of a picaxe I know it is reinventing the wheel but it what interests me . Getting back to the LoRa units I have to say their performance is quite impressive and at some stage I will probably have a go with them if I can just get my head around the programming it's not an insurmountable problem for me but it would be a project in it's own right. I have admit if I had a go at a HAB I would go for a pico the idea of having a 1kg payload land in the middle of a motorway is one I would sooner not have to contemplate, but with my track record I would probably call it Expendable(1)!

Getting back on topic, even the picaxe store has rf modules that are not the highest pedigree but they fill a niche and are affordable, which is very much the case with the units I have been using for testing, there is often not much of a spec sheet to go with these units, the receiver I have been using is a superregen it is very fussy about the voltage it gets fed 5V is ok at 3.5V it goes deaf I'm guessing there is not enough gain at lower voltages to get regeneration going properly as I can't hear any quench noise.
My main motivation for posting was most modules for the picaxe tend to be plug in write the code and if it bombs it's most likely the code, I may just daft/unlucky but then again it occurred to me someone else may be having trouble with code that bombs when tied to an RF circuit and is OK without the RF link and can't work out what is going on.

 

[manuka]

In today's cheap & reliable RF IC era, 433MHz super regen. modules of the type you're using (below ?) are akin to using steam engines to power a motorbike. AVOID THEM- especially since far superior & more versatile ASK modules now abound at much the same price.

LoRa™ is a magnificent technology & has really taken wing in recent months. If you use "2 chip" TTL friendly LoRa™ modules (such as Dorji's or Microchip's new & versatile RN2483) trials become quite straight forward with even a 08M2. PICAXEable insights at my Instructable may be of interest.

Although single chip "7 a side" SX127x LoRa™ modules like HopeRF's are cheaper, they need SPI interfacing & probably better suit more professional & HAB (High Altitude Balloon) work.

 

[gaz57bag]

In today's cheap & reliable RF IC era, 433MHz super regen. modules of the type you're using (below ?) are akin to using steam engines to power a motorbike. AVOID THEM- especially since far superior & more versatile ASK modules now abound at much the same price.

LoRa™ is a magnificent technology & has really taken wing in recent months. If you use "2 chip" TTL friendly LoRa™ modules (such as Dorji's or Microchip's new & versatile RN2483) trials become quite straight forward with even a 08M2. PICAXEable insights at my Instructable may be of interest.

Single chip LoRa™ modules like HopeRF's however are cheaper,but need SPI interfacing & probably better suit more professional & HAB (High Altitude Balloon) work.

manuka I will try to be brief, I agree with what you say but I'm more the Lego type rather than Meccano a lot of what I do probably would not be too difficult for a well motivated 10 year old, I get more fun out of wherever possible scratch building (I'm early Blue Peter generation) even though it will probably end up getting scrapped. Have you built a crystal set they are pretty hopeless a basic set pulls in one dominant station and nothing much else, then the but what if... element kicks in next thing you have a a double tuned wave trapped set with forward bias for the diode why? why not!
An awful lot of hobbyists publications tend to be backward looking one of the electronics mags recently had a circuit for a courtesy light for cars I thought it was standard on all cars these days if I see another direct conversion receiver for 80M in the press I will probably go mad I have a few copies of the 1950's hobbies weekly (yes weekly) some of the ideas in them are still being touted today.
A steam driven motor bike, food for thought but I think it has been done, I have been toying with the idea of an autonomous vehicle (probably a boat) using 21'century knowledge but 1950's 1960's technology just for the sheer hell of it, its nuts I know but its something different .
You're instructable was very interesting when I next commit to a project that has to be on spec,on time and on budget if it involves telemetry I will be giving it a second look.