Many people on AMSAT use DCI brand passband filters at their antennas to cut down on front end overload and splatter from other services. These multi-resonator filters typically cover several MHz of bandwidth to cover entire sections of the Amateur Bands and block things out of band..
When I asked if they could be tuned narrower with all resonators favoring the same single frequency, their answer kept coming back YES, the bandwidth is 500 kHz. But they did not define what the “bandwidth” meant.
Today, they sent me a revised spec sheet for their two meter filter when tuned to a single frequency. Now they fully specify what the bandwidth is. Here are the numbers:
- 3 dB is 0.5 MHz
-20 dB is 1.25 MHz
-40 dB is 2.3 MHz
-60 dB is 4 MHz
This is useful information for those needing a single frequency filter.
Bob, WB4APR