Re: [linrad] Quietening computer noise

[Richard Hosking <richardh@xxxxxxxxxxxxxxxx]

Many thanks for the info.
The system is just a crude lashup at the moment as a starting point. The 
front end board is just sitting on the bench, with separate power 
supplies for that and the the LO which is a previously built sig gen.  
The PC is a cheap second hand box for the experiment (AUS$70 only) The 
antenna is just a long wire at present. That may be the best place to 
start. I will incorporate the front end board and the LO into a shielded 
case remote from the PC and filter the audio (Perhaps balance?) between 
them, and put up a decent antenna with a separate ground.

Richard


wb9uwa@xxxxxxxxxxx wrote:

> Hi Richard,
>
> I haven't seen it directly mentioned here yet, so it might be worth mentioning.
> You did not say what you are using for an antenna.
> Be very careful that the PC does not become part of that antenna.
> If you just use a simple wire connected to the RX, your PC is sure to
> be part of your ground plane and will generate noise. I am not so sure
> that double sheilded coax is needed at HF, but it is important that
> the antenna be remotely located and have its own local independant
> ground, depending on antenna type. None of my outdoor HF antennas
> pick up RFI from the PC.
>
> 73, Jim Shaffer, WB9UWA.
>
> On 2 May 2004 at 20:58, Richard Hosking wrote:
>
>  
> > Dear all
> > I have managed to recieve signals on HF using two SBL-1 mixers driven
> > by a quadrature LO (AD9854) and a couple of low noise opamps (NE5534).
> > Linrad runs in direct conversion I/Q mode. The main limiting factor at
> > present is noise from both computer and monitor. The sound card is bog
> > standard and the machine is a PII 400 MHz running RH9, but with only
> > 64MB of RAM
> >
> > Questions
> > The max filter bandwidth appears to be about 2 KHz on SSB, and
> > narrower on AM  - if I try to make it wider nothing happens. Is this
> > due to RAM and processor limitations?
> >
> > How to get rid of that computer noise? ( I have made no attempt
> > whatever so far)
> >
> > Thanks in advance
> >
> > Richard
> >
> >
> >    
>
>
>
>  


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