Most SDR dongles are not any good performers as quality receivers and will easily overload and have artifacts and images in its reception as they lack any kind of RF filtering.
What are the frequency span you would like to receive and are there any particular frequency span that you want to reduce? PAR electronics can tune a bandpass or notch filter for you. It's something like $150 and upwards for a individual tuned PAR filter. The SDRPlay receivers have filters and a better receiver specification and the RSP1a are something like $110. I have a clone MSI.SDR and it performs much better than a SDR-RTL.
But if you have severe interference from a strong transmitter, if you have a scanner and that also have images, then an external filter are probably the only good solution. If that strong signal are coming only from one direction then a directional antenna pointed to reduce that signal as much as possible might help, or two normal antennas connected together and the coax lenght to one antenna, or one antenna being moved, so that the received signal are cancelled from that direction at that particular frequency. There are noise cancelers that simulate different lenghts of that coax or that the second antenna are moved and the canceler can be tuned to cancel out the offending transmitter signal.
/Ubbe
