[hpsdr] Questions about Mercury data

[David McQuate]

Doug,

(1) In Setup, PowerSDR has a calibration capability.  You tell it the 
frequency and power level.  It observes the signal with Mercury's input 
attenuator both in and out, and stores the appropriate calibration 
factors.  Kiss Konsole uses fixed approximate calibration factors.

(2) ep6 data is derived from the raw ADC samples through digital 
downconversion, low-pass filtering and sample rate reduction 
(decimation).  The noise floor is reduced as the final sample rate is 
decreased.  The relationship between the ADC samples and the final 
24-bit I & Q values is variable only in the selection of digital 
down-conversion frequency and decimation factor.  The values are 2s 
complement binary.  The low-pass filtering and decimation process (two 
CIC sections, followed by a FIR filter) result in the additional bits.  
I'm not sure what the maximum and minimum values are.

(3) ep4 data is simply a snapshot of a group of 16384 contiguous raw ADC 
samples, taken at a rate of 122.88 M samples per second.  (Older 
firmware produced blocks of 4096 samples.)  The values are 2s complement 
(signed) binary, so they have a range of -32768 to +32767.

(4) Unless you have a narrow-band antenna or a high-pass filter in the 
antenna feed, I'd expect very large broadcast-band signals--their 
transmitters are generally much more powerful than ham transmitters, 
their antennas are huge, and they may be located very close to you!

(5) I'm surprised that ep4 packets continue to be sent when the wideband 
data is "turned off".  I'll take a look.  If it's true, sounds like a 
firmware bug.

73,
Dave
WA8YWQ



On 9/27/2012 4:08 PM, Doug Adams wrote:
> ***** High Performance Software Defined Radio Discussion List *****
>
>
>
> I have a few questions concerning Mercury:
>
>   * Is there any easy way, without a lot of test equipment to
>     determine where the noise floor should be positioned on the
>     Panadapter display All of the software available provides a
>     "calibration" adjustment, how do you determine where to set that
>     adjustment?
>   * Normal receiver data (i.e. ep6 data):
>       o What will be the expected range of values? I can see that it
>         is made up of 24-bit samples. Is the data in some fixed
>         relationship to the input signal, i.e. a specific input values
>         generates a specific data value or is it somehow variable?
>   * Wide Bandscope data from Mercury (i.e. ep4 data):
>       o How is the Wide Bandscope data generated, I'm assuming that it
>         is a decimated version of the Normal receiver data.
>       o What will be the expected range of values? I can see that it
>         is made up of 16-bit samples. Is the data in some fixed
>         relationship to the input signal, i.e. a specific input values
>         generates a specific data value or is it somehow variable?
>         When I look at the frequency-domain signal on my bandscope, it
>         seems that the broadcast band stuff is huge but most of the
>         signals at higher frequencies are at much lower levels.
>       o It appears that when you tell Mercury not to send bandscope
>         data (in the StartStop Packet, 0x01 vs 0x03) I still see
>         incoming ep4 packets but the data in them is a fixed value. Is
>         that correct or am I doing something wrong?
>
>
> I've been following this list for some time and have found it very 
> helpful for learning more about openHPSDR. Thanks for all the good 
> information.
>
> Doug Adams - K3TZR
> douglas.adams at me.com <mailto:douglas.adams at me.com>
>
>
>
>
>
>
>
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-- 
Clear Stream Technologies

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