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Re: [linrad] Quietening computer noise
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.
>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:
>>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
>>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