[TangerineSDR] In pursuit of low noise: fiber USB cables?

[Tom McDermott]

Hi John - by doing your own DC distribution you can do a much better job of
RFI suppression.

- Consider using coaxial cable to distribute the DC power.
- Common-mode filters on the DC coax can help the cable do a good job of
keeping the RFI inside.
- RFI can come from either (or both) ends of the circuit, Low pass filters
on both ends can reduce that problem.
- Use of ferrite beads in the series DC+ filters can reduce the higher
frequency components of the noise because
   the bead itself usually has low parallel capacitance compared to some
other inductor types.  You may need to worry
   about saturation of the bead at higher currents.

-- Tom, N5EG






-

On Tue, Feb 27, 2024 at 12:31 PM John Ackermann N8UR via TangerineSDR <
tangerinesdr at lists.tapr.org> wrote:

> Hi Tom --
>
> I think you're absolutely right on #3.  After fiddling with the cables
> that noise seems to have largely gone away.  But we have other noise
> sources in the building, and moving the radio 100 or so feet away can't
> hurt.  And besides, it sounds like a cool idea!
>
> A DC power line would go along with the fiber.  It would be regulated
> and filtered at the far end to provide the required voltages.  Hopefully
> with shielded twisted pair, good PSRR regulators etc., you could keep
> that from contributing much noise.
>
> I don't know if the cable I linked to is anything like the best choice;
> more research would be needed on that.  There are solutions that cost
> from <$100 to >$1500.  There are also 10 Gbit and even some 20 Gbit
> converters available if 5 Gbit isn't enough.
>
> 73,
> John
> ----
> On 2/27/24 15:05, Tom McDermott via TangerineSDR wrote:
> > Hi John - some things to consider about the USB extender cable:
> >
> > 1. How will the RX888 be powered when using this cable?
> > 2. In the one review - the extender was being used to bring back data
> > from an HDMI switch to a computer.
> > HDMI switches are usually powered from the HDMI cables or via a local DC
> > input, thus not needing power from the USB port.
> > 3. I'm guessing much of the hash is due to the DC USB power from the
> > computer radiating as RFI on the cable
> > when the shield is making poor or no contact.
> >
> > -- Tom, N5EG
> >
> >
> > On Tue, Feb 27, 2024 at 8:26 AM John Ackermann N8UR via TangerineSDR
> > <tangerinesdr at lists.tapr.org <mailto:tangerinesdr at lists.tapr.org>>
> wrote:
> >
> >     I had the idea last night that we could put an RX888 and GPSDO at the
> >     base of our active antenna and run an optical USB3 cable back to the
> >     host computer. That would move the radio far away from all the
> >     computers
> >     and other noise in the shack. The only copper connection would be for
> >     power, and we could filter the hell out of that.
> >
> >     Something like this:
> >
> https://www.amazon.com/Elecan-Extension-Extender-Transfer-Keyboard/dp/B0BNGW5225/ref=asc_df_B0BNGW5225
> <
> https://www.amazon.com/Elecan-Extension-Extender-Transfer-Keyboard/dp/B0BNGW5225/ref=asc_df_B0BNGW5225
> >
> >
> >     might do the trick. (Note -- I don't know if 5gbps is sufficient for
> >     the
> >     RX888, but if not there are 10 and 10 gb cables available for more
> >     money.)
> >
> >     A challenge is powering the transceiver at the far end, but that
> >     shouldn't be too hard to do.
> >
> >     Has anyone considered this?
> >
> >     73,
> >     John
> >
> >     --
> >     TangerineSDR mailing list
> >     TangerineSDR at lists.tapr.org <mailto:TangerineSDR at lists.tapr.org>
> >     http://lists.tapr.org/mailman/listinfo/tangerinesdr_lists.tapr.org
> >     <http://lists.tapr.org/mailman/listinfo/tangerinesdr_lists.tapr.org>
> >
> >
>
> --
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>
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