MARS filters?

David Salomon

Question for Tim...

Specifically, what changes were done to the pre-selector filters for the MARS mod.  Asking because there are numerous MARS frequencies I operate on that are not immediately above/below the ham bands.  When I operate on those, the radio is always in WIDE mode, i.e. no pre-selectors.  As I get closer to the ham bands, and with less bandwidth displayed, it goes out of WIDE mode and the pre-selector filters kick in, which, as you know, significantly quiets the receive.  I'd like to know what frequency ranges the pre-selectors cover pre and post MARS mod.

73 - David, AG4F

Tim - W4TME

The MARS filters, which is the add-on hardware filter bank to extend transmit outside of the ham bands, only operates on the transmit signal path.  The filters in the RX signal path, the band-specific preselectors are designed for ham band use, so there is no change in the preselector switch points.  Since bandpass filters have a roll-off on the ends, we extend them out beyond the edges to ensure we have the band covered properly. 

The logic as to whether or not to enable the preselectors is dependent on the panadapter bandwidth.  So if you are at the top or bottom of the band and you have the panadapter extended out beyond the band edges to the point where the preslector filter loses effectiveness, we switch the preslector out of the RX signal path and the WIDE indicator shows up on the panadpater display even though your slice may be in a ham band. We have not published the switch points of the preselectors, but you can figure it out by changing the panadapter low or upper-end frequency until the filter switches out.

David Salomon

Thanks, Tim.  I was aware of the wide vs pre-selector switch, and had already figured out where the switch was made.  It's good to know the details of the MARS mod.

73 - David, AG4F