RF433 using 433.722 Mhz and not 433.92Mhz

Community General Discussion
1

Hello,

I have an old device (temperature sensor) that uses 433, but the frequency does not seem to be on 433.92 Mhz, but 433.722 Mhz.

I used rtl_433 with an SDR to find the frequency it is using.

I have a 433.92 Mhz receiver with a pot on it, when I purchased it it said that it could be adjusted between 315 Mhz and 433 Mhz. problem is I am not sure which way to turn the pot and how much to do so to change the 433.92 Mhz to 433.722 Mhz. also would I need to change the antenna, I would not think so for just a few Khz change?

I am using an Arduino UNO to try and receive the signals using 433utils sketches.

any assistance would be appreciated.

cheers,
Pasquale

2

Post a link to the product page or data sheet for that receiver -- I think you are mistaken about the tuning adjustment.

The inexpensive 433.92 MHz receivers that look like the one below are rather broad band, and should work fine with a transmitter operating at 433.722 MHz.

Capture

3

That would be a software change to tell the IC which frequency to use. Likely to be a one-time change.

4

And what happened when you tried, did it not work ?

5

433.92 is the center frequency for the ISM band. which is actually quite a range of frequencies. So 433.722 is not so far off and could be wrong based on your receiving equipment calibration.

The antennas are of such poor quality, changing them makes no sense.

6

IMG_20220929_135806
IMG_20220929_1358061920×1440 146 KB

Pin configuration1
Pin configuration1902×769 385 KB

Yes it is like the one you show.. I have attached a picture of my setup

7

I do not get any data I in the serial console...

Not at home right now, can upload the sketch later.. but it is from 433utils..

8

You need an antenna. 17 cm of straight wire is a good choice for 433 MHz.

The 315 MHz and 433 MHz receivers are superregenerative, and differ only in their choice of tuned circuit, which is the green coil form in the center of the board. The frequency is somewhat adjustable using the ferrite "slug" in the coil form (held in place by red glue).

9

The receive bandwidth is extremely wide on that receiver. Such a small difference in frequency won't have any effect. Leave the variable cap alone,,,,, (it's not a pot).

As mentioned, it won't change between 433 and 315 mhz.

10

Ok thank you I will leave the inductor/capacitor allow and verify my Arduino sketch.. maybe bring the device closer to the reciever..

Cheers

11

Did you attach an antenna to the transmitter and receiver? Picture isn't clear but it looks like not. Needs about 17cm wire as mentioned.

12

No, the IC is an op amp.

13

I was thinking about the transmitter IC.

14

Right, for most of them. But this one uses the "can" ... it's a fixed frequency crystal controlled oscillator unless I am mistaken.

15

Then I guess the only possible modulation scheme is on-off modulation, AKA CW. Must have more devices that control the modulation.

16

O I did not, thought it has an onboard antenna.. will look at adding it. 11 cm of any coper wire?

17

17 cm of straight copper wire (quarter wavelength at 434 MHz).

18

Okwill give it a try tomorrow, thank you for the info..

19

The 17cm antenna length is a calculation of what "should" resonate at that frequency. But it is a a best guess because the ground circuit becomes half of the antenna in that configuration. So the size and length of the unit and connecting wires will change the optimum match. But the main thing is to move from no antenna to some antenna. In practice, once you get a wire on there you are 95% there. To get to 100% you need a proper antenna and balun to isolate it from the circuit... but for this device it's a rapidly diminishing return for your efforts.

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