433MHz transmitter Coil missing [SOLVED]

433MHz transmitter Coil missing

Hello there,

I received my 433MHz pairs of transmiters and wondered that the little coil on the transmitter was missing (on all 4!)
but at first sight I thinked “why not?”
I tried a lot of example (VirtualWire & RadioHead) and nothing was functionning (I didn’t get a transmission),
so:

  • what is this little coil intended for?
  • is there an electrical schema to understand it?
  • how to make it with simple wire to add it on the board?

if i understand you right you have the transmitter model with only 1 coil instead of 2?
in the one coil model they have replaced the smaller coil(Air-Core Inductor) with a smd inductor (look at the backside of the board)

if you have the receiver that usually comes with this transmitter i would suggest if possible to get a better receiver, if not make sure you have caps close to receiver and transmitter and have soldered on the antennas on transmitter and receiver, 17cm wire (best if its straight), The antenna hole are the hole in the upper corner of the transmitter(the text on these can be all over the place and not always easy to understand…)

Hope this helps some best of luck

thank you very much!
it helps me at least to not consider that the little coil is missing!
(but I still don’t understand how it works)
I already added antennas (17.3cm) on my first pair transmiter/receiver, but after my unsuccesfull trials I doubdted maybe one was not functionning, so I tried with another pair (without antenna because it is said that it should work at close range) and then another one but without any change (= not working).
I guess now my problem is elsewhere than hardware…

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Its worth monitoring the current taken by the transmitter as this will increase on transmission and helps give confindence in it.

An RF sniffer is really useful when playing with RF modules: https://en.wikipedia.org/wiki/RF_probe

These RF modules are very crude BTW, so don't expect miracles. They may have a minimum useful range as well as a maximum, due to being AM rather than FM. Try them at least a few metres apart to be sure you're not just deafening the receiver.

I say this every time these are mentioned, i know - but the green receivers that ship paired with those transmitters suck, like really bad. The RXB-12 (avail on ebay for a buck or so each, little yellow pcb) get much better range (order of magnitude) and doesnt get into a bad state where it doesnt receive anything when used at close range, and works at 3.3 or 5v instead of 5v only.

The shitty green transmitters are fine though (though the stx-882 gets better performance at low voltage)

Theres no reason for the transmitter to have a coil at all, at least one you can see. Heres an example. https://www.aliexpress.com/item/2sets-lot-433MHz-100meters-Wireless-Module-kit-ASK-transmitter-STX882-ASK-receiver-SRX882-4pcs-copper-spring/32685978219.html

This type also uses a Superhet receiver which are far better than the horrible superregens. The helicals arnt that great though, and should only be used if you are really short of space.

I dont know why people continue to buy those horrible ASK radios when for around the same price you can get these. https://www.aliexpress.com/item/HC-11-HC11-433MHz-wireless-RF-serial-UART-module-CC1101-5V-3V-AT-command/32424814620.html?spm=2114.search0604.3.1.338652308IoyY4&ws_ab_test=searchweb0_0,searchweb201602_6_10065_10068_10130_10890_10547_319_10546_317_10548_10696_453_10084_454_10083_10618_10307_537_536_10131_10902_10132_10133_10059_10884_10887_321_322_10103,searchweb201603_70,ppcSwitch_0&algo_expid=336020d4-ba23-482f-b067-17a6781f42bd-0&algo_pvid=336020d4-ba23-482f-b067-17a6781f42bd&transAbTest=ae803_5

Identical to HC12s from IO perspective and 1/2 the price or more, not compatible with HC12s though as they use a the CC1101 radio chipset.

mauried: I dont know why people continue to buy those horrible ASK radios when for around the same price you can get these. https://www.aliexpress.com/item/HC-11-HC11-433MHz-wireless-RF-serial-UART-module-CC1101-5V-3V-AT-command/32424814620.html?spm=2114.search0604.3.1.338652308IoyY4&

+1

It seems that the saving of a few cents is far more important than ease of use and supperior performance.

I thank you all for your answers.
my problem has been solved by program (#include <RH_ASK.h>), and the subject is closed (I got communication!) about “missing coil”.
+
by the way, Without Antenna it’s working/communicating from 1cm to 8m in free air!

adrenalinos:
I thank you all for your answers.
my problem has been solved by program (#include <RH_ASK.h>), and the subject is closed (I got communication!) about “missing coil”.
+
by the way, Without Antenna it’s working/communicating from 1cm to 8m in free air!

So the coil is used on some modules as the antenna right? While other modules that look similar use a different structure (not coil) as the antenna … and that antenna is already built-in with the module, right?

1 Like

Southpark: So the coil is used on some modules as the antenna right? While other modules that look similar use a different structure (not coil) as the antenna .... and that antenna is already built-in with the module, right?

No, the coil is not designed to be used as the antenna on these modules. However, there is sufficient RF energy leaking that a receiver at close range can detect the signal in spite of not having a proper antenna.

MrMark: No, the coil is not designed to be used as the antenna on these modules. However, there is sufficient RF energy leaking that a receiver at close range can detect the signal in spite of not having a proper antenna.

Thanks MrMark. Close range ..... as in right next to each other?

At 433 MHz ..... quarter wavelength is around 17 cm. Without any substantial antenna ...... this module isn't going to transmit very far at all, right?

Hey there. So, I just wanted to chime in here. I understand that all your questions are answered, however in the hopes that i can help you out further. These pair don’t operate on the same voltage. THEY DO NOT BOTH OPERATE AT 5V!

The reciever is designed to operate on a 5V power supply and you hook it up directly to your arduinos 5V line. It will be fine on that power supply.

THE TRANSMITTER IS DESIGNED TO OPERATE ON 6-12V! You will never get more than a few meters if you dont boost the power to your transmitter. You cannot just plug it directly into your arduino and expect to get the 200-400m range that they are rated for.

Yes you can easily get over 100m range from these. They are great. However, you must use something like a transistor or an optocoupler to key your rf signal. If you dont know what that means, you should do some more research on how this type of radio works.

Hi,
i too had the same problem, and i tried manchester, RH, and virtualwire libraries,
unfortunately it did not work for me, so can you please post what your working code was ? for both Rx & Tx