[hpsdr] TAPR Hermes - Noise on Audio Out

[David McQuate]

Does the audio out signal change if you change the sample rate (in 
PowerSDR setup, on the audio tab)?

If you turn on the panadapter display, does it look "normal"?  With the 
Rx antenna disconnected the noise floor should be fairly uniform, and 
something like -100 dBm, depending on the sample rate.

How about the "scope" display?  With no antenna, it should show a fairly 
narrow line--a low noise level.

If these two are normal, that means that the ADC samples are being 
properly transmitted from Hermes to the PC, and there isn't a major 
problem in the signal processing.  If that's the case, then the problem 
probably is in the audio output circuitry.

If the scope display shows large pulses or spikes, then the problem is 
occurring before the audio output circuits.

73,
Dave
WA8YWQ

On 11/20/2012 9:11 PM, Ron Nelson wrote:
> ***** High Performance Software Defined Radio Discussion List *****
>
> Hi,
>
> I have my TAPR Hermes working using PowerSDR, however, there is loud 
> noise on the audio output independent of the RX input. The noise 
> consists of  sharp spikes, 2 V p-p with a period of about 2.8 ms.  I 
> do hear stations with an antenna connected, but the noise level is 
> comparable to audio from strong stations.
>
> I think I have ruled out external local sources:
>
> Tried DC power from a switching power supply, a regulated lab bench 
> supply and a battery.
>
> Connected Ethernet to PC directly and via a Linksys router.
>
> Tested with and without antennas. Always used 50 Ohm dummy load on Tx 
> out.
>
> Tried two locations and turned off all other PCs and devices nearby.
>
> Put in the Anan case and grounded it. None of the above made any 
> change to the noise.
>
> Suggestions please?
>
> 73
> Ron NR5ON
> _______________________________________________
> HPSDR Discussion List
> To post msg: hpsdr at openhpsdr.org
> Subscription help: 
> http://lists.openhpsdr.org/listinfo.cgi/hpsdr-openhpsdr.org
> HPSDR web page: http://openhpsdr.org
> Archives: http://lists.openhpsdr.org/pipermail/hpsdr-openhpsdr.org/
>
>

-- 
Clear Stream Technologies


 1353538362.0