I recently bought an RTL-SDR
(https://www.nooelec.com/store/nesdr-smart-sdr.html), a small radio
receiver that is powered by the USB connector on the punchbox. It
digitizes the received radio signal and sends the digital information to
the punchbox for processing via USB.

It turns out that the computer generates to much noise for the receiver
to operate in close proximity to the punchbox.

So, I have to move the receiver and/or the antenna further away from the
computer. I choose to move the receiver as low loss coax for the uhf
band is pricey.

So, I bought a high end 10 foot USB 2.0 extension cable, with 2 layers
of shielding, and emi suppressors (ferrite) on each end of the cable.
The cable has 24 gauge power bus conductors, mote than adequate for
powering my RTL-SDR receiver. The RTL-SDR receiver uses 370 ma, worst
case, so the 24 gauge power conductors in the cable should be adequate.

The RTL-SDR unit has an internal (smt type) emi absorber on the power
input terminal. The computer is a very dirty place in terms of rf noise,
and having rf noise on the USB lines is like rolling out the welcome
wagon for rf interference to the RTL-SDR receiver.

The new USB cable works fine for the smaller usb flash drives I have,
but it causes the RTL-SDR device and my USB HDD unit to fail when
connected through the new cable. Neither of the higher power devices are
recognized. The RTL-SDR requires the full USB 2.0 throughput, without
it, it can't send data fast enough to enable the software in the
punchbox to function. Both the HDD and the RTL-SDR work fine when
plugged (directly) into any of the ports on the computer (without the
extension cable).

I concluded that I need to roll my own cable. That way, I know the cable
itself is proper. I can buy the usb ends for the extension cable and
solder them to the cable.

However, I can't find the technical specs for the cable, so I don't know
which type of raw cable to buy....in order to insure my homebrew cable
works at it's full capacity (which is 480 MB/sec). There are USB
repeater cables that extend the max cable length out to 50 feet, but
they're expensive, they draw a lot of power and they don't work at the
full data rate for USB 2.0. And, none of the repeater cables have
shielding at the housing for the driver electronics.

I've thought about using an ethernet cable and putting usb connectors on
the ethernet cable. But, ethernet uses balanced transmission line
(twisted pair)...it might not work well for usb because USB doesn't use
a balanced line-so there is little benefit to be had by moving to
ethernet cable for usb data transmission.

I sure wish the RTL-SDR had an ehernet cable connector instead of a USB
connector!

My problem is I cannot find the usb 2.0 specification that outlines the
critical parameters for the cable itself. Any ideas?

Sorry to be so long winded::>

Art




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