[hpsdr] Alex Bug?

[Scott Cowling]

The firmware in Mercury selects the filter based on the frequency.

According to the comments in the code, the frequency sent to Mercury 
by PowerSDR is "the indicated frequency less the 9kHz IF". As a 
consequence, the firmware adds 9kHz to the frequency to determine 
which filter to engage.

If GHPSDR does not do the same, then the switch points will be different.

Here are the switch points for the current Mercury code:

if
freq > 29700000 then use 6m LPF
else if
freq > 21450000 then use 12/10m LPF
else if
freq > 14350000 then so use 17/15m LPF
else if
freq > 7300000 then use 30/20m LPF
else if
freq > 4000000 then use 60/40m LPF
else if
freq > 2000000 then use 80m LPF
else
use 160m LPF

where "freq" is the frequency data (in Hz) + 9000 for IF correction.

If GHPSDR sends the real frequency (instead of the frequency 
including IF offset), then these switch points would all be 9 kHz 
lower on your GHPSDR dial.

If your tuning step was 1kHz, it would change filters between 
1,991,000 Hz and 1,992,000 Hz, so it would look like a switch point of 1992kHz.

73,
Scotty WA2DFI

At 20:28 2011-08-31 -0500, Bill Tracey wrote:
>***** High Performance Software Defined Radio Discussion List *****
>
>It is the firmware that selects the filters ... in Mercury I believe 
>but not 100% sure of that.  Idea of putting it out there was that to 
>make the  firmware smart enough to select the filters since it 
>already knows the frequency.   Suspect we've got an off by 8 error 
>in the math somewhere in the Verilog code  or have lost the bottom 3 
>bits somewhere
>
>
>Regards,
>
>Bill
>
>At 07:34 PM 8/31/2011, george byrkit wrote:
>>***** High Performance Software Defined Radio Discussion List *****
>>
>>I think this is in the updated firmware for Penelope or mercury or Ozy or
>>Metis.  I do NOT think that this is an application program thing.  All the
>>app does is choose the antenna and gain specified for the band when the band
>>is chosen/changed/selected.  It is, I think, below the application in the
>>HPSDR boards where the frequency is decoded and turned into selecting the
>>correct bandpass filter.
>>
>>73,
>>George K9TRV
>
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