[hpsdr] Alex Filter Switching Frequencies

[Phil Harman]

Thanks to all who commented on the proposed changes to the Alex Filter 
switching frequencies.

The consensus appears to be that we keep the current automatic selection 
mode, with modified switching frequencies, but add a mode whereby the PC can 
specifically set the switching frequencies.

The automatic switching frequencies will be, for the HPFs:

 if (frequency < 1.8MHz)  bypass
 else if (frequency < 6.5MHz)  1.5MHz HPF
 else if (frequency < 9.5MHz) 6.5MHz HPF
 else if (frequency < 13MHz)  9.5MHz HPF
 else if (frequency < 20MHz)  13MHz HPF
 else 20MHz HPF

and for the LPFs:

if (frequency > 32.0 MHz) 6m LPF
else if (frequency > 22.0 MHz) 12/10m LPF
else if (frequency > 15.0 MHz) 17/15m LPF
else if (frequency > 8.0 MHz) 30/20m LPF
else if (frequency > 4.5 MHz) 60/40m LPF
else if (frequency > 2.2 MHz)  80m LPF
else 160m LPF

I've updated the USB Protocol (V1.33 in SVN under \Documentation)  to 
provide for PC selection of the switching frequencies. Could those that are 
writing PC code please review the suggested protocol and let me know if you 
would prefer an alternative implementation.

I'll advise when the revised FPGA code is available.

Thanks.

73 Phil...VK6APH


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