I bought some 915 MHz bandpass filters for use on my Meshcore node. Below are the sweeps of the filter. I got my filter from Aliexpress here (affiliate link). Remember to choose the correct frequency range.
As you can see, this is the overall sweep from 840 MHz to 990 MHz with a centre frequency of 915 MHz (Meshcore). What I found interesting was the smooth rolloff at the high end, down to around -50dB at 975 MHz-ish. On the bottom there is a sharp drop off and some interesting bumps but all well below at worse -40dB.
The insertion loss at 915 MHz is 1.58dB. This is very acceptable for a filter like this. For context, setting TX power to 22dBm is about 158mW. With the filter inline this would drop to ~115mW or so.
The lower 3dB point is 897.250 MHz and the upper 3dB point is 934.500 MHz, so an effective bandwidth of 37.25 MHz.
