[hpsdr] Alex Filter Switching Frequencies

[tbruns]

I would like to suggest with respect to (3) that instead of removing the 
filter selection from the FPGA code that the code be kept as fallback 
behaviour and the PC code that specifically selects the filters would as 
a first step execute a command to disable hardware selection. This way 
users wouldn't lose Alex altogether if they upgrade their firmware prior 
to the PC client filter selection code being available in their PC 
client of choice.

73 Tom KC5L

On 09/09/2011 07:09 AM, Phil Harman wrote:
> ***** High Performance Software Defined Radio Discussion List *****
>
> All,
>
> Good to see that Alex is making its way into users hands and appears to
> be working OK.
>
> We need to review just how the various filters on the Alex boards are
> selected .
>
> When I first wrote the Mercury FPGA code that drives Alex, PowerSDR was
> using a 9kHz IF. Hence the frequency sent to the HPSDR boards was the
> indicated frequency less 9kHz. In the Mercury FPGA code I added 9kHz to
> the frequency being sent by PowerSDR and used this to select the
> approproate HPF and LPF pair.
>
> The idea was that the 'intelligence' as to what filters to select was in
> the FPGA code and there was no need for the PC code to send anything
> more than the required frequency - which it did by default.
>
> I gather that the latest versions of PowerSDR use a 0Hz IF in which case
> the filter selection will be incorrect at the high end of some bands. A
> while ago I did try setting the IF frequency to 0Hz in PowerSDR but from
> memory I found the AM demodulator was distorting at zero beat. I can't
> reproduce this problem so assume it has been fixed.
>
> We have a number of options in relation to how the filters are selected
> - these include:
>
> 1. Simply remove the 9kHz offset code in the Mercury FPGA code and
> switch filters at the current frequencies. The current logic is:-
>
> For the HPFs
> if (frequency < 1.5MHz) 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 > 29.7MHz) 6m LPF
>
> else if (frequency > 21.45MHz) 12/10m LPF
>
> else if (frequency > 14.35MHz) 17/15m LPF
>
> else if (frequency > 7.3MHz) 30/20m LPF
>
> else if (frequency > 4MHz) 60/40m LPF
>
> else if (frequency > 2MHz) 80m LPF
>
> else 160m LPF
>
> 2. Remove the 9kHz offset and alter the frequencies that the filters
> switch at. This would help MARS operators.
>
> 3. Remove the filter slection from the FPGA code and instead allow the
> PC code to specifically select the filters. This could be simply linked
> to the Band selected or a full GUI similar to that used to select the
> Penny(Lane) open collector outputs or the Alex antenna selections.
>
> When working through the above we also need to consider split/full
> duplex operation and the use of transverters.
>
> Perhaps we could have a preliminary discussion following the Teamspeak
> session on Friday (USA) evening followed by some brainstorming via the
> reflector?
>
> 73 Phil....VK6APH
>
>
>
>
>
>
>
>
>
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