Usual source of components for Meshtastic node builders are sites selling goods coming from China. There is always concern on quality of products coming from there. Here is measurement of 868 MHz Band Filter I did on item I got from AliExpress.
Actual filter is PCB SMD component. The rest is just PCB that allows attaching SMA male and SMA female connectors to it and everything is wrapped in transparent heat shrink tube. Everything is pretty small: 35 x 8 x 7 mm. It is meant to be used by inserting it between 868 MHz device and antenna.
Claimed characteristics:
Center frequency: 868 MHz
1dB bandwidth: 10 MHz
Tape interpolation loss: < 2.0 dB
Out-of-band suppression:
> 42dB@700 MHz
> [email protected] GHz
Impedance: 50 Ohms
Maximum load power: 20 dBm(100mw)
Here is what I measured using NanoVNA:
Center frequency: 868.503 MHz
1dB bandwidth: 10 MHz
3dB bandwidth: 14.1566 MHz
6dB bandwidth: 15.6301 MHz
Tape interpolation loss: 2.709 dB
Impedance: 49.1-j5.78 Ohms
You can check graph:
What is conclusion? This filter is actually fine. Bandwidth is good and suppression becomes pretty steep. However, it inserts bit high loss – 2.7 dB. As I learned from other people who also use such filters, insertion loss can be significantly lower if you are lucky to get excellent specimen.
At the end, I recon it is not bad for 7 EUR filter. It can not just help if you are unlucky to have lots of RFI at the site, but make connections possible at all. It is good to have some for case they are needed.