If you place a good band-pass filter like Flightaware Light Blue or Dark Blue Filter or a Cavity Filter beween Antenna and Receiver (or Antenna & LNA if you are using a LNA without builtin filter), then all the FM and VHF UHF out of band frequencies will be eliminated by filter and wont reach the Receiver or LNA. This will prevent:
(1) Overloading & de-sensing of receiver or of LNA
(2) Creation of harmonics by mixing & cross-modulation of various out of band frequencies in the amplifier stages of receiver or LNA.
Please see “Scan 3 of 3” below which shows how adding a Filter Between Antenna and Receiver eliminates unwanted RF signals picked by Antenna.
Spektrum - How-to Speedily Scan RF Noise in band 24MHz ~ 1800MHz
The results of scans are below:
The scan 1 shows RF noise picked by antenna and processed without any filter , The scans 2 & 3 were done with filters, and show how filters remove this noise.
Scan 1 of 3 - FA Antenna + Generic DVB-T (no internal or external filter)
CLICK ON IMAGE TO SEE LARGER SIZE
Scan 2 of 3 - FA Antenna + ProStick Plus (Only Internal filter of ProStick Plus. No External filter)
CLICK ON IMAGE TO SEE LARGER SIZE
Scan 3 of 3 - FA Antenna + ProStick Plus (with internal filter) + External Filter (FA Light Blue)
CLICK ON IMAGE TO SEE LARGER SIZE
