Sometimes the "other" frequency produces a better signal at your location. I did prove that several times with the NASA Engine by finding a new ship by changing the frequency! The problem then came in that some existing contacts disappeared! I tried the new chip which everyone raved about on the ShipPlotter group and found it much better than the original. However, i had the chance to obtain a "Dual reception" Comar SLR200, and find that very good indeed. However, this only has a 9 pin COM port outlet, so if AirNav only allow a USB input from their rig, I am back to square one!
Cheers
Peter