Understanding specifying multiple frequencies

[Mike]

Hello,

I've been using rtl_443 recently to scan for a couple 433mhz weather devices and it works great. Recently I learned that other sensors I have broadcast on 345mhz. Testing this out with rtl_433 picks up these devices perfectly.

Now I am experimenting with specifying two frequencies for rtl_433 to scan and, my understanding, is that rtl_433 will not scan multiple frequencies at once, rather I need to specify a time period to scan for each frequency using -H. Which to me reads if these 345mhz devices broadcast during a time when rtl_433 is scanning 433mhz, those will be missed (in my case, I'd prefer not to delay a read of these devices).

1) Is my understanding correct? So if I'd want rtl_433 to scan both frequencies at once, I'd need two usb SDRs?

2) Are there any usb devices that can scan multiple frequencies at once?

Thanks for a great product!

[Mike]

I guess another question - is there a way to use one usb device to scan two frequencies and ensure I don't miss updates? Or would getting a second SDR device be best?

[Barry Smith]

You can use the hop feature -H  I use it to scan 433 and 915 example rtl_433 -f 433920000 -f 915000000 -H 20

change the hop interval 20 (seconds) to what ever you wish,  I use 14 seconds. A little experimenting with interval is required. you may miss a few results here and there. I use rtl_433  to decode atlas weather station and Ecowitt soil moisture testers. They run automations for my awning wind alert automatic in and soil moisture and rain fall for garden irrigation system and etc..

[Christian Z.]

if I'd want rtl_433 to scan both frequencies at once, I'd need two usb SDRs?

It's always frequencies ranges (center freq +/- half of sample rate), mostly referred to as "bands".

If you want to receive all transmissions on two bands then that's recommended.

Sometimes you would be okay to miss every other transmission. If you know both devices send every 60 seconds, then stay on the band for 70 seconds.

Or switch fast and randomly receive from one or the other band. Likely best choose a co-prime with all send intervals so you don't sync with one sender for long periods.

 

2) Are there any usb devices that can scan multiple frequencies at once?

 There's the LimeSDRs and the SDRplays with two receviers.

 

is there a way to use one usb device to scan two frequencies and ensure I don't miss updates? Or would getting a second SDR device be best?

 

If you exactly know when to expect transmission, e.g. "last +58s", and you keep memory of the last transmissions and then implement a smart switching...

RTL-SDRs are cheap enough to not go to that trouble, and people use 7 receivers on a single Raspi without problems ;)

[Mike]

Thank you all!