433MHz transmitter and receiver

[kenwawa01]

Hi!
By default in rtl_433 project we use receivers to analyse TPMS data. I was wondering how complicated it would be also to generate messages to be sent to tpms module. Something like tpms sensor(s) simulator.

Which device could be then used for receiving/transmitting data? Which one would you recommend?

Do you know any project which could be some kind of example for transmitting tpms data (simulating tpms sensors)?

All links would be welcomed.

[zuckschwerdt]

You'd need hardware capable of sending FSK. Could be some SDR with TX or dedicated tranceivers like a CC1101.

[kenwawa01]

Thanks for answering. I'm just entering 433MHz wold thus my questions might be very basic.

Could you give few example of those SDRs with TX you would recommend to work with rtl_433 project?

Does any DVB tuners have the possibility to "produce signal"? Sth like: https://pl.aliexpress.com/item/1005006420997014.html I'm using it for recording 433MHz and it works surprisingly well.

What about SDRs like this https://pl.aliexpress.com/item/1005005952566458.html ?

With CC1101, I've never seen it in USB version to be connected to laptop. Sure you can use usb-rs232 interface but it will not be very stable "mechanically". I mean it might not be convenient to be use longer with laptop unless you will put everything in nice box and solder permanently.

Will rtl_433 work without problems with CC1101 connected via usb-rs232 interface?

[zuckschwerdt]

rtl_433 has no TX capability. The RTL-SDR you linked do not have TX, no "tuners" have that. You get TX with SDRs in a higher price range. E.g. LimeSDR, PlutoSDR, HackRF.

The CC1101 (and other such transceivers) need I2C (not UART serial) and good programming skills.

[kenwawa01]

Sure I know that rtl_433 has no TX capability. But when buying I would like to buy sth which will work with rtl_433 in read mode and later I could try to find some other projects (plus perhaps modify them) to use the same device in write mode.

Do you perhaps know any fork rtl_433 projects which work with CC1101?

[pswiatki]

Btw, will rtl_433 for reading tpms messages (no TX) work with DVB-T2 usb tuners based on RTL2832P (the last character is different), ex. sth like that: https://pl.aliexpress.com/item/1005003105710626.html

If this is a question - then yes it will. NOTE: I would strongly recommend using dongles that are considered Proper, see: https://www.rtl-sdr.com/buy-rtl-sdr-dvb-t-dongles/ as those are much more stable than some cheap ones ("clones").

[kenwawa01]

Yes, it was the question. :P Thanks for this hint. :) For simple use those dvb-t/t2 should be enough, at least i hope, and u can always use them for watching tv. Those rtl-sdr v3/v4 are not for tv watching right?

[pswiatki]

Dear @kenwawa01 V3/V4 contain exactly the same chip RTL2832, which does DVB-T demodulation and decoding. Note: a different driver is required on the host system to receive and decode digital, terrestrial TV. Hope this helps.

[kenwawa01]

But are you sure that it's only the question of this main chip? I've done some small searching and I found many suggestion that v3/v4 are enough for dvb-t but not good enough for dvb-t2 and it will not work. Sure I didn't check it by myself.

[pswiatki]

Don't know anything about DVB-T2. Nevertheless, this is outside of the above topic (rtl_433), so I can care less about DVB-T support. The important thing for RTL-SDR is that the dongles can act as cheap and effective RF samplers with tuners capable of receiving signals from a wide range of frequencies (the newer ones can also do direct sampling of HF). This is enough to know about those devices.

[kenwawa01]

Ok I bought device with RTL2832P https://pl.aliexpress.com/item/1005001812444617.html and it works much worse than the one with RTL2832U https://pl.aliexpress.com/item/1005006385049099.html

This P is loosing many messages which were read without problems with U. Moreover with P I have quite often messages which I didn't notice in case of U version.

bit_buffer_add_bit: Warning: row count limit (50 rows) reached

I tried using -g=-5 or -g=5 or similar values but it doesn't help. I tried also -Y autolevel -M level -M noise but I'm not able to improve scanning.

The only thing which helps a bit is to reduce the antenna length but it still gives worse results than in case of U version.

Is that more antenna problem or this new device has much worse radio reception or might it be that rtl_433 code is missing sth for this new version, some kind of automatic signal leveling etc.?

[zuckschwerdt]

bit_buffer_add_bit: Warning: row count limit (50 rows) reached is a sign of noise that looks like data. You could compare both receivers using a SDR UI, or grab samples with both (or record for a short time) and compare in https://triq.org/pdv/

[kenwawa01]

It might be that P is more noisy. But with P I'm missing more or less 50% of correct messages which I was able to catch without problems with U. Thus it suggest that P might be so noisy that it cannot read the correct messages. Ex. if tpms sensor repeat the same message 4 times, I get ex. repetition 1 and repetition 3 only. Wile with U nothing missed. Sure in the same conditions.

I can't compare two in the more detailed way as you suggest, as U was borrowed and I don't have it any longer. I bought P for myself and it seems it was not the best idea.

I'm only not sure if it's purely hardware problem or P might have sth slightly different in software part and it requires ex. some additional parameters when being used...?

[zuckschwerdt]

Interesting, thanks! Take a look at a sample or recording anyway, you might notice something in the spectrogram, could be interference or such?