[hpsdr] Penelope Troubleshooting

[David McQuate]

USM-281A seems to be a 50 MHz bandwidth 'scope.  It won't display the 
ADC clock (122.88MHz), or some of the faster signals. The lower data 
bits going to the ADC may be changing too fast to see accurately, but 
you should be able to see the slower-changing higher data bits.  And 
here we don't need to measure them accurately, but just see if they are 
changing, especially see that that they are not all always low.

You'll want to use a 10-x probe so that the scope probe doesn't load 
down the data lines too much.  Even a 10-x probe may have too much 
capacitance to avoid affecting the performance--but again, all we need 
to know is if the data from the FPGA to the DAC is changing, and we 
don't intend to leave the scope probe on while we're actually using 
Penelope.

73,
Dave
WA8YWQ

On 7/29/2012 2:10 PM, Stephen West-Fisher wrote:
> ***** High Performance Software Defined Radio Discussion List *****
>
> Thanks! That's the kind of info I'm looking for.
> However, I'm working with a USM-281A so nanoseconds will be hard to count
> :-)
>
> --
> Stephen West-Fisher
> N4IK
>
>
> -----Original Message-----
> From: hpsdr-bounces at lists.openhpsdr.org
> [mailto:hpsdr-bounces at lists.openhpsdr.org] On Behalf Of David McQuate
> Sent: Saturday, July 28, 2012 11:31 PM
> To: hpsdr at lists.openhpsdr.org
> Subject: Re: [hpsdr] Penelope Troubleshooting
>
> ***** High Performance Software Defined Radio Discussion List *****
>
> The fact that LED7 changes blink rate--to indicate PTT change--shows that
> the FPGA is at least partially alive and working properly.  If Bob's
> software / firmware suggestions don't take care of the problem, and you have
> an oscilloscope, you might carefully probe the DAC input data lines while
> TUN is active: bits 0 - 13 on U7 pins 14 - 1.  The lower bits should have
> high frequency square waves, the higher bits, lower frequency.  These are
> the digitized sine wave generated by PowerSDR to produce the CW TUNE signal.
> The clock input, U7 pin 28 should have a very fast square wave -- 8 ns
> period.  If they're changing, but there's no signal on JP3 pin 2, there's a
> problem with the
> DAC.   Check that pins 24, 25 & pin 27 are +3.3 volts.
>
> With TUN active, Atlas C19 should have digital signals--the transmit data--I
> & Q data from the PC via Ozy.  The data is sent using "NWire", a digital
> pulse-width modulation, with a "0" represented by a short high pulse, and a
> "1" by a longer high pulse.  Thus when sending all zeros -- as when PTT or
> TUNE are not active -- there will still be many fast pulses, in bursts with
> a 48 kHz repetition rate.
>
> Atlas C20 should also have digital sgnals -- the command and control data
> broadcast by Ozy to Mercury & Penelope.
>
> 73,
> Dave
> WA8YWQ
>
>
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