[hpsdr] Wide bandscope

[Bob Cowdery]

Ok, I'm trying to understand it. I've played with manual Alex filter 
settings so I can see a bit better what's going on. I'm assuming that 
with multiple rx the Alex filters on auto are opened up so I would need 
to manually apply the correct filters for the radio with focus or use 
auto if listening to multiple rx. As far as the WBS is concerned it's 
not very useful with the noise floor so high that signals can't be seen. 
Is there no way to improve that?

Bob - G3UKB


On 4/23/2018 2:50 PM, Tom McDermott wrote:
> HI Bob -
>
> The sample rate of the ADC is 122.88 Ms/s. The samples occur at 
> 1/122.88e6, or
> one 16-bit sample every 8.13 nanoseconds.   This is about 3 gigabits 
> per second.
>
> So the hardware takes 16384 time-consecutive samples, then sends them 
> to the host.
> Then it waits about 75 milliseconds      (This is the large-timegap.)
> Then it takes another 16384 time-consecutive samples....
>
> There are 256 real samples per USB frame.   So  16384/256 = 64 USB 
> buffers.
> Metis packs 2 USB frames into one Ethernet packet, so 32 Ethernet 
> packets per
> 16384 real samples.
>
> -- Tom, N5EG
>
>
>
>
> On Mon, Apr 23, 2018 at 5:59 AM, Bob Cowdery <bob at bobcowdery.plus.com 
> <mailto:bob at bobcowdery.plus.com>> wrote:
>
>     Hi Tom,
>
>     Thanks for the info and the code. I must admit I'm still pretty
>     confused on several fronts.
>
>      1. In my code I'm collection 16384 samples starting when the
>         sequence number is dividable by 32 with no remainder. I don't
>         know if that's right as I didn't understand what you meant by
>         a large time gap.
>      2. To confuse matters the KISS code I have which I think is the
>         latest only collects 4096 samples. I think my firmware is the
>         latest and it looks like I updated it in 2014.
>      3. I've been away from this so long I forgot Alex sits in front
>         and is set to auto. Then I thought, what does Alex do on auto
>         when several receivers are running. If I run one rx my wbs
>         display looks a lot more like what I see on KISS but with 3
>         receivers the noise floor is much higher and signals are hidden.
>
>     Bob - G3UKB
>
>
>     On 4/23/2018 12:32 PM, Tom McDermott wrote:
>>     Hi Bob -
>>
>>     The number of samples was increased from 4096 to 16384 a few
>>     years ago in Protocol 1 FPGA code.
>>     I don't know the effective FPGA revision number, but it was
>>     probably 2013 or so.
>>
>>     The data rate would be very high if sent continuously, so 16k
>>     samples are time-contiguous but then
>>     there is a large time gap until another 16k contiguous time set,
>>     etc.  I treat each block as a 16k vector
>>     of time samples.
>>
>>     These are 16-bit raw samples, 2's complement fixed point, real
>>     (not complex), and have not been decimated.
>>     So the noise floor is not lowered by decimator integration.   If
>>     you do an 16k FFT on the vector you will
>>     get a two-sided result.
>>
>>     If there is a bandpass filter in front of the ADC then the
>>     spectra will be shaped.   In practice most
>>     receive antennas / tuners will also shape the spectra.  A very
>>     broadband antenna and no filtering
>>     would be needed to achieve relatively flat spectra.
>>
>>     I implemented a wideband gnuradio module for this, you can look
>>     at the C++ code at
>>     https://github.com/Tom-McDermott/gr-hpsdr/blob/master/lib/hermesWB_impl.cc
>>     <https://github.com/Tom-McDermott/gr-hpsdr/blob/master/lib/hermesWB_impl.cc>
>>     I don't know if that will help as much of the processing is
>>     gnuradio specific.
>>
>>     -- Tom, N5EG
>>
>>
>
>

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