Introduction: 433 MHz Coil Loaded Antenna

Picture of 433 MHz Coil Loaded Antenna

In my 433 MHz projects I have been using a cheap (0.70 cnts) pair of Tx/Rx
modules. I have mostly used the transmitter and that is actually fairly OK with just a simple 1/4 lambda antenna, but is open for improvement

The receiver however is a bit crappy: without antenna the reach is maybe no further than a meter, but even with a 1/4 lambda antenna it is marginally more, even with free Line of Sight.

For any serious project that involved receiving data it seemed I needed the much better (and more expensive) RXB8 receiver. But as said, also the reach of the transmitter could use a bit of improvement.

However, when mining the internet for a coil antenna (trying to improve on the lengthy 17.2 cm stick antenna) I came across a design of Ben Schueler, apparently once published in elektor magazine. A reference to Ben's pdf (back up) would suffice to build it, but so is my picture and I can add my experience with it as well.

It is a so called coil loaded design consisting of 0.6mm wire wrapped around a 2.5mm core.
The picture gives a clear description: a length of 25 cm wire should be enough. At the base it is 17 mm long. Then goes into 16 turns over a 2.5 mm diameter core (Ben advises to use 1.5mm²black installation wire for this. I just used a screwdriver)

The results with this antenna are very good. The distance (with the cheap receiver as well as the transmitter) that can be covered easily goes to 25 m with line of sight, but also in-house the distance will be increased reaching other rooms with concrete walls in between, were earlier 3 meters with line of sight would be pushing the limits already.

I am not the only one with this experience. Many people confirm to me that it dramatically increased the range of the cheap Tx/Rx pair, read the comments!

Comments

TariqM1 (author)2017-11-21

hello

diy_bloke (author)2017-08-07

Ben, Thanks. That design changed my 433 world. When i was just using the 1/4 wave whip antenna, I couldnt do anything serious with those cheap transmitters and then I found your design: BIG difference and I mean BIG!!!!.

I trust I gave you enough credit :-).

I am slowly moving away from 433 in favour of the Wemos... but I just seamlessly shifted my existing 433 infrastructure into Openhab with a simple MQTT-433 Gateway, again with your antenna. Even at 3 Volt there is considerable reach with the el cheapo transmitters, yet I use it at 5Volt, but may try 9Volt.
Thanks again for your design

surrogard (author)diy_bloke2017-10-16

Hi diy_bloke,

I'm currently buildung exactly the same thing here, a 433MHz-MQTT Gateway. What microcontroller did you use? I have an ESP8266-12F in a "Witty Cloud" board. Just am fiddeling with the voltages, the Witty Cloud exposes 5V but the GPIOs work on 3V3...

I'm gonna build this antenna for sure, when I was playing with the receiver before the reception was abysmal, but what do you expect without any antenna :D

diy_bloke (author)surrogard2017-10-16

using a Wemos board (D1 mini). I am not sure how the witty cloud board exposes 5V to the pins. It has a 3v3 adapter and one can use the voltage from that.
Though the 433MHz Transmitter works better on 5V vcc, it is no problem (as I experienced) to have the signal come from a 5V pin.

yes, antenna makes a big difference. Before I made this one, only using a 17 cm wire, 433 Mhz wasnt a serious option

surrogard (author)diy_bloke2017-10-17

I ended up using a voltage divider for the receivers data pin because the ESP on the witty cloud runs with 3v3 and the GPIOs expect that too. The receiver itself is rated at 5V anyway...

I already received some codes (even without antenna, will build that now), but unfortunately not the temp/humidity sensors I have :D
Have to try some other library, I'm using the ESPiLight one right now.
Do you know if I can run several libraries from the same GPIO interrupt?

diy_bloke (author)surrogard2017-10-18

indeed for the Receiver it is a different matter. I understand though the receiver does work on 3V3 too and unlike the transmitter that wouldnt affect its sensitivity. Having said that, those cheap receivers are usually crap whereas the transmitter si fairly OK
ESPILight is the pilight library I think. I dont have any experience with that.
Whether you can run 2 libraries from the same pin depends much on the libraries itself. I know I have run RCSwitch and RemoteSwitch from one pin

surrogard (author)diy_bloke2017-10-18

Oh ok, but doesn't matter, it is running and receiving something... I'm gonna let the lib send the RAW data to me for some debugging, perhaps I can add that protocol in use...

Looks like running two interrupt routines from one interrupt is not possible, the newer attachment overrides the older one and I would have to change the libraries to "merge" them...
I'll simply connect the receiver to several pins (hopefully they are 'interrupt-able') and then I have several possibilities for libs. Although the ESPiLight is already quite good.

You are sending, right? So you are triggering a pin, for the receiver I have to use interrupts and sometimes the libraries are doing that by themselves.

Btw.: the maker of ESPiLight has already done exactly what I'm doing here, but I'm still gonna do it by myself, you know the drill ;)

https://github.com/puuu/MQTT433gateway

diy_bloke (author)surrogard2017-10-19

yes you are fully correct. I am sending. Though I have done projects that involved receiving, my main use is sending. The receivers are commercial wall switches.
Indeed, with interrupts and one pin it is a whole different ballgame.
Yes had seen the pilight MQTT433gateway. You also may want to check github for a guy called "1technophile" he has an IR/433/MQTT/RFM69 hub

Dangerously Explosive (author)2017-10-14

These are awesome. I made them a while ago (and I think I left a
comment about it) and they work quite nicely. One question I have,
though. Which library do you use for your modules (if any)? I use the
Radio Head for Arduino and it doesn't seem to support the ability to
send different commands based on sensor input. The reason I ask is, I'm
trying to use them for robot communication, which really only works if
the robot can send/receive more than one set of signals.

There
don't seem to be many other reliable libraries... So I was wondering how
you do it since it sounds like you've been using these things for a
while.

I have used 3 different libraries, depending on what I wanted.

Manchester library - for between arduinoor attiny communication

RCSwitch for remote control

yet i prefer the

RemoteSwitch for that purpose and I used a completely updated fork of that one.

https://github.com/yoh-there/RemoteSwitch

If you need it for a robot i presume the Manchester or virtualwire library would be the best

Thanks! I'll look into those... And hopefully get my robot working!

Good luck :-)

Tylerlee12 (author)2017-08-29

Anyone know what stores in the Midwest would carry semi-rigid copper wire of this size for this use? Radioshack is gone from my area.

diy_bloke (author)Tylerlee122017-08-31

Sorry, cant help you there

Tylerlee12 (author)diy_bloke2017-09-08

No problem! Any idea what temper bare copper wire would work best?

I used 18 gauge copper modelling wire. Found it in the hardware isle at Lowe's, it was low down under some random stuff at the end of the isle. They also had steel wire, from 24 gauge to 18 gauge. That would've worked too.

diy_bloke (author)Tylerlee122017-09-09

Not sure what you mean with 'temper bare copper'

Home Depot, Lowes, Harbor Freight, Amazon.com, Fry's Electronics... The list goes on. You can find it at almost any hardware store, if you know where to look. If you don't, well, that's why stores still have employees to help you and haven't switched over to robots quite yet.

JBSchueler (author)2017-08-05

Nice to read people still like to build this design I described many years ago :)

I still using this design for low-cost 433MHz transmitters, receivers and transceivers. No need to match the antenna for these low-cost devices and the range improves already a lot compared to the normal antennas those are shipped with (or no antenna at all).

Kind regards,

Ben Schueler

BotondB2 made it! (author)2017-06-15

Thank you for the article! I've been trying basically any idea I find on the internet to increase the range of my 433 MHz modules, but so far I haven't succeeded. I've made two of these coil loaded antennas. I measured everything very precisely, the coils also have the correct turn count - I've checked it repeatedly. But unfortunately attaching the antennas has effectively halved the already very poor (2-3 m) range of my modules compared to the straight ones.

BotondB2 (author)BotondB22017-06-15

Ok, I've since tried something else. I soldered the antennas to another pair of modules and - magically - the range improved significantly and the error rate dropped to zero. I don't have any time left today to measure the range and experiment further but it seems that the original modules were defective. So it really works! I highly recommend everyone to try it.

diy_bloke (author)BotondB22017-08-03

That is good to hear. Thank you for the feedback

BrendanG27 (author)2017-06-06

I believe these are the same rx/tx devices you have used. Can you tell me if you have removed the existing antenna and replaced with the coiled ones? My transmitter seems to have two coils connected together if I'm following the traces correctly.

diy_bloke (author)BrendanG272017-06-09

no i didnt remove anything. just added the antenna to where it says "ANT"

QuentinB28 made it! (author)2017-06-06

Used a screw to nicely loop the wire, worked like a charm.

diy_bloke (author)QuentinB282017-06-06

good idea. Thanks for the pics

frownbreaker (author)2017-06-05

Thanks so much for a clear, well laid out explanation. I have some old 433mHz sockets with poor antenna and my transmitter (3.3v supply from an ESP8266) works fine with my newer 433mHz units around the house 10-15m away from the transmitter (walls, stairs etc) but my old STATUS brand units would work most of the time but some of the more distant ones (3m away) would not always work. I think the remote for the STATUS sockets takes a 12v battery so the antenna on these old units is not great. This is compounded by the fact I'm using them to power up / off active speakers 10 in the same room, and AV Kit sub etc all mounted on metal wall stands. I did have everything working but if the transmitter moved away from its sweet spot (e.g. when I reprogrammed the ESP8266 and had to connect it to my computer).

I followed you instructions using some wire that the local telco guy had left in our street and just soldering your design to the ANT via on the PCB means the transmitter can be positioned casually without any problems. The same transmitter also controls lights and other appliances around the house.

Thanks so much :)

diy_bloke (author)frownbreaker2017-06-06

my pleasure. I am happy it works well for you, just as it did for me.

Dangerously Explosive made it! (author)2017-05-28

These things are awesome! Just the right size for what I need. By the way, 25cm is just a little short, I would suggest using about 25.5cm of wire and cutting off the extra.

Thanks for yr feedback. I am actually still very happy with them. Brought Rf communication with 433 Mhz on a serious level.
Yes, always good to use some extra wire. If you use a core to wind them on is only a fraction thicker that could easily grab some extra material.
I really encourage anybody using RF433MHz to give these a try

Nitrus015 (author)2017-05-05

I put it on my 433mHz receiver (for my driveway gate remotes), and increased the range by approximately 10 meters. It used to have a helical before, the receiver came with that one by default.
I used a single strand from a Cat5 LAN cable, solid core.
So I'd say this was a success :)

diy_bloke (author)Nitrus0152017-05-05

Well that is good to hear. The single strand of a CAT 5 is rather thin I think. Try with slightly thicker wire and see what that does if you have some free time :-)

vhaxos (author)2017-04-25

great work! first antenna I tried, and works great. Improve distance from 5m to 45m or maybe more!

diy_bloke (author)vhaxos2017-04-26

Thanks, I am glad it helped you

RobertDan (author)2017-04-17

This worked exceedingly well! I tested indoors line of site up to 35 feet. Was getting 5 to 10 feet without an antennae.

For me I disliked the overall length of the antennae, I was wanting something more compact. I seen somebody commented that the $5 Helical antennae on e-bay worked well too. I took a look and they're much cheaper than $5. Still... who wants to wait for it to be shipped from China? What I did see was a helical antennae that stopped at the turns and did not rise above past it. (rubber duck type antennae as they call it, without the rubber covering). That's more ideal for me!

For 433Mhz the length was 32mm, had 23 turns with a gap in each turn that was about the width of the wire (exactly like a spring), I do not know what gauge wire it was . I went to Home Depot and bough the smallest solid core wire I could find. Turned out to be 20 AWG (bell wire). Cut off approx. 42mm of wire, stripped off the coating so the wire would be bare copper. Left a straight length of 3mm long (+ 1mm or more for the bend that would go into the module's antennae hole), then tightly wound it around a small screwdriver of the remaining wire. This came out to be 27 turns and was shorter than 32mm in length. I stretched out the "springiness" of the coiled wires to obtain 32mm of length. It worked just great! Got a confirmed 35 feet of solid communication. Plus.... instead of sticking up perpendicular to the receiving module I was able to bend it parallel behind the receiving module which is about 3 to 5 mm shorter than the module itself without any loss in distance from my simple test.

Thank you for sharing this information with us!

diy_bloke (author)RobertDan2017-04-20

Thanks Robert for sharing yr experience. Indeed there are several different antenna designs. The one I made just worked great for me so I didnt have the need to make another. It also works if I put it perpendicular to my board as you van see in one of my pics. Mine has a good reach as well, goes about 10 meters through my house, throug a solid glass window and then well into the garden. Certainly 35 feet if not more. Also reaches one story up.
But should I need a shorter antenna I will surely try the design you described

bogdan94 (author)2017-04-05

I have a question, as I'm planning to make those. Does it matter if the wire is insulated or not? Is a single cable from an UTP cable good for this? Should I make two antennas? One for TX and one for Rx? Thanks alot, great instructable!

diy_bloke (author)bogdan942017-04-06

I am not an antenna specialist, but I have mine with the insulation on and the antenna worked much better than a whip. I am not sure how it would work without the insulation, simply because I never tried and had no need for it as it would reach all over my house.
I am not sure if UTP cable is the proper material. Too flexible. I use some semi-rigid connection wires. The sort you would normally solder on a PCB or a connector.

yes, you need to make two, one for the Tx and one for the Rx.
i am sure the design can be improved but I already went from a few with a whip, to all over my 2 story house and garden. I do admit my whip did not have a groundplane

bogdan94 made it! (author)diy_bloke2017-04-07

Hmm, I just made those, but it seems like the modules work even worse than before soldering the antennas, I don't get correct commands at distances greater than 15, maybe 20 centimeters.

Here is a picture of them, maybe I got something wrong.

Thanks for the reply!

diy_bloke (author)bogdan942017-04-09

I must say that surprises me greatly, because til now I only heard people having great improvement.
Your antennaś look OK in the picture, so I start to wonder if maybe it is the wrong wire. The first thing I think of is that maybe you have used stranded wire?
Really needs to be solidcore.
Anther possibility is the insulation. Try one without the plastic insulation

Haenzel (author)2016-12-31

Worked perfectly. I slightly changed mine though. Used a wooden cocktail stick ( that has the proper diameter) to turn the wire. Left the stick in place, cut it at the proper length and shrink tubed it. I epoxied the base of the stick to the board, making the antenna somewhat idiot proof...

diy_bloke (author)Haenzel2017-01-01

that is actually a pretty good idea. no doubt a wooden core will have different properties than an air core, but i guess it makes no difference

Bobv40 (author)2016-09-02

Hi,

I've tried multiple tips and trick regarding 433 Mhz Antenna Desgins and this is the only one which really makes a difference ! I am very happy with that.. One question though. Receiving the radio waves is one thing, but it starts with transmitting... Does this design also improves things at the transmitter side, or just use the 17 cm wire there ?

Thanks again..

diy_bloke (author)Bobv402016-09-04

Tnx for your kind words. I use it at both sides

cranphin (author)2016-07-29

Just as a note, the cheap 'Helical antenna 433MHz' for 5 a dollar on ebay actually work quite well too (not surprising, their very similar in design, 21 ish turns of 5mm ish diameter, so that's about 33 cm in them, + 1 cm at the straight end) :)

diy_bloke (author)cranphin2016-07-30

thanks. I have seen similar designs being sold, but I found the prices (e.g. 5 USD) always a bit steep for what is basically a piece of wire. I am sure that 'my' design (factually it isnt my design, I just came across it),, might not be the one and only best, maybe an extra winding or a bigger airgap or slightly longer may give great results as well, but let me put it like this: when I was still using the straight wire antenna, I was convinced the 433 Mhz projects were useless. More than 2-3 meters were already a problem while with the helical antenna I reach all over my house (2 stories and from the front of my house well into the back yard (about 25 meters, + 1 wall)

cranphin (author)diy_bloke2016-07-30

Oh, I quite agree! And I'm quite thankful for your design, it's what made me try the ebay ones ;) Jus thought I'd mention those, since I couldn't find anywhere mentioning if their good or not, turns out they are! :) And their 5 for 1 dollar, so pretty cheap! In fact I chose them cause it was cheaper to get them then to order some bendy wire XD (Not much of a DIY scene in this country, and seems solid core wire isn't as common on ebay).

diy_bloke (author)cranphin2016-07-30

yes I got that. I saw thy sell for 75 cts us pr 20 at aliexpress. Your comment actually prompted me to dig in some more 433 MHz antenna designs and you can find from very simple to extremely complicated :-)
this one seems one of the simplest but get much better range than the straight wire. I think placing the antennas such that they have the same orientation, may also make a few decibels difference

AmoorS1 (author)2016-06-26

Hello, I'm a complete newbie when it comes to such things, but I wanted to get a helical antenna for it's directional properties. I want it to be very limited (About 40~60 degrees) does this help? From what I've read online it should be fairly directional, but does this particular setup add that directionality factor? Also, I would love to know from which side I would best receive a signal in case it is indeed directional. Thanks a lot for this amazing write up though.

diy_bloke (author)AmoorS12016-06-27

Sorry Amoor but it is not directional. It may look a bit like a helical antenna but it isnt. As far as I understand the directional helical antennas have a base plate that reflects the signal. In that case the directionality is lengthwise from the helix.
Thanks for your kind words

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