[hpsdr] Transmit noise problem ?

[Mike Naruta]

Thanks Al.  With Ozy-Janus disconnected from the
SDR-1000 / PC (only the Atlas power supply
connected and on), I measured between the SDR-1000
ground and Atlas J20 0V.  No AC at all.  The
Atlas power supply shares the same Tripp Iso-Bar
outlets with the PC and SDR-1000 Astron PS.

I don't think it is a ground loop.  The problem
is still there when I insert my four 1:1 isolation
transformers in the Janus I/Q in/out leads.

I've tried different configurations on Atlas:

Ozy 1 Janus 2

Ozy 2 Janus 1

Ozy 1 Janus 6

Ozy 6 Janus 1

Ozy 3 Janus 4



The noise doesn't look like 60 Hz hum.  On a
20 MHz scope (floating ground) looking at
Janus I/Q out, the lowest wave I can resolve
is less than a 1 microsecond period, with
other frequencies on it.  The amplitude is
about 15 mV P-P.  I think it was present both
in transmit and receive.

The noise appears equal amplitude on both channels.
If I transmit in CW, I see the regular I/Q signals,
90 degrees out of phase.


A stumper.


Mike - AA8K


a.groff wrote:
> Mike,
>    Sounds like the SDR-1000 is fine.  I can't imagine how the software 
> could do this.
>    Two thoughts come to mind...
>    1)  a Noisy ground system.  This would have the characteristics of .. 
> in an external receiver the signal would have
>             a) characteristics of 60 Hz hum and would be present as soon 
> as the rig is keyed with drive already at zero i.e no need to excite the 
> the output first. 
>             b) characteristics of a pulsing noise ( 1-2 pulses per 
> second ) but you have to excite it to get it started.  This could be 
> caused by common ground loop with the high current power supply feeding 
> the radio.
>             With no audio cables connected directly between the O/J and 
> sdr-1000 is there any AC/DC voltage differential between the chassis of 
> the SDR-1000 and the O/J power supply ground lead ?  Even a 100 mv or 
> less could be a problem.
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> 
>    or 2)  A defective ADC channel on Janus.  If you disconnect the TX 
> I&Q from the SDR-1000 and you look with a scope at the each of the TX I 
> & Q signals coming out of Janus,  does the noise look the same?  Likely 
> only one channel would be defective.  If the noise is on both channels, 
> the problem could be ADC ( Janus internal ) power related ( but not 
> likely if the RX is working ).  At normal power out, can you get good TX 
> image rejection ?
> 
> Got a friend you can barrow an O/J from ?
> 
> AL, K0VM
> 

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