Re: [Flexradio] RF Noise from Presonus Firebox

[Ross]

Thanks Tim, I would appreciate learning if it works. If I cant find an NZ distributor, I would get one from the source you mention . Regards Ross   ----- Original Message ----- From: Tim Ellison To: Ross ; Guy Atkins Sent: Tuesday, January 10, 2006 4:42 PM Subject: RE: [Flexradio] RF Noise from Presonus Firebox Ross & Guy,   I talked to a buddy of mine in the recording business.  He built and runs his own studio.  He said most Firewire cables are not the best made.  He had to go to a very high end one to ensure quality digital audio transfer.  He suggested these high quality Firewire cables.  I am going to give this one a try and let you know how it works.   http://www.cablestogo.com/product.asp?cat%5Fid=216&sku=29495   Their may be a New Zealand distributor.  I’m not sure.   -Tim --- Tim Ellison ( [EMAIL PROTECTED] ) Integrated Technical Services ( http://www.itsco.com ) From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Ross Sent: Monday, January 09, 2006 9:47 PM To: Guy Atkins Cc: FlexRadio@flex-radio.biz Subject: Re: [Flexradio] RF Noise from Presonus Firebox   Guy, Thanks for your email, its nice to know someone else has noticed a problem with the Presonus Firebox. Like you I tried earthing the Firebox, to no avail. Thanks for the tip about the toroid, I had one here, but it also is not the problem. It appears to be coming down the firewire cable. The noise is particularly obvious  ( in fact very obvious) on my FT1000 which is just attached to a wire antenna. Remove the Firewire cable and the FT1000 is quiet, just normal rural atmospheric noise. So unless I can stop the noise from the Firewire somehow, the only answer may be to try the Delta 44 internal soundcard I have here.. Any suggestions gratefully accepted, as the presonus is a nice unit. Regards Ross   Original Message ----- From: Guy Atkins To: Ross ; FlexRadio@flex-radio.biz Sent: Tuesday, January 10, 2006 2:44 PM Subject: RE: [Flexradio] RF Noise from Presonus Firebox   Hi Ross,   That was good timing of your inquiry about the Firebox noise! I just returned from a four-day DXpedition (chasing foreign MW and tropical bands) to the Washington coast, and encountered noise from my Firebox, too. This was my first serious use of my relatively-new SDR-1000 and I had not noticed any noise at my home location (fairly RF-quiet).   However, in a DC-only DXpedition setting with zero noise other than atmospheric, any RFI is immediately noticed. I tracked down a pulsing, broadband hissing noise to the Firewire DC  input, which is connected to my deep-cycle batteries via a distribution system feeding all other DC gear. With all other equipment turned off, I noticed no difference in the noise level when unplugging the I/O cables and the Firewire cable.  The only thing remaining was radiation from the unit's case or power cable, or  conduction via the power cable. I tried temporarily grounding the Firebox's metal case, without effect.   I happened to have a Amidon FT-140-J torroid core (1.40" diameter) on hand, so I did a field mod of cramming as many turns of the DC cable through the torroid as would fit. The coaxial DC connector is attached less than an inch past the torroid.   Voila... noise gone! The only noises remaining were very low-level spikes and buzzes here and there, visible on the panadapter. I tracked these down to RFI emanating from the Compaq X1000US laptop screen (noises change pitch and intensity when I touch my hand to the surrounding LCD cover, aluminum in the X1000 series). I don't know if the RFI is coming directly from the laptop (screen) casing, or going out through the various parallel & USB cables. I've always thought this was a pretty quiet laptop, but the SDR-1000 shows up any little signal in a RF-quiet environment. In the future I'm going to experiment with RFI clamp-on ferrites on every cable.   By the way, after calibrating the SDR-1000's level with a XG-1, the background noise with Beverage antenna attached was around -132 dBm at medium preamp setting, and -140 to -144 dBm at the high setting. Very impressive! These readings were just after local dawn at the coast, where noise levels can be eerily low in mid-winters (WA State has the fewest T-storm days per year in the continental USA). A Beverage antenna aimed out over the ocean at dawn knocks down domestic mediumwave and tropical bands frequencies to the east, leaving weak DX from Asia and the Pacific in the clear.   So...try a torroid core to clamp down the noise from the Firebox. If your setup is like mine, the RFI is coming from the power cable. The "J" series Amidon core is one I've often used over the years for constructing impedance matching transformers, baluns, etc.   73,   Guy Atkins Puyallup, WA   __________ NOD32 1.1357 (20060109) Information __________ This message was checked by NOD32 antivirus system. http://www.eset.com