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Re: [Xylo-SDR] [Flexradio] Proof-of-concept successful!
LVDS is made for a tightly twisted pair with 100 Ohm impedance, a pair in
a CAT5e cable is exactly what is meant to be used with. Does anyone know
what the characteristic impedance of a USB cable is? If not, then it's
best to stay away from anything unknown.
It's a transmission line from the transmitter to the receiver and should
be treated as such including impedance matching so you do not get
reflections, shortcuts will lead to phase noise.
As far as a connector, a CAT5e RJ45 connector is meant for that
impedance, and does an excellent job.
At 11:30 AM 1/31/2006, Christopher T. Day wrote:
Could you use
standard USB cables with a type A connector on the end where you have
room and a type mini-B on the end where you don't? USB is a single
differential twisted pair with additional gnd and Vbuss wires rated to
420 Mbits/second. Be sure it's protected if someone accidentally plugs in
a real USB at either end.
Chris - AE6VK
From: Phil Harman
Sent: Sunday, January 29, 2006 12:31 AM
To: FlexRadio@flex-radio.biz; Xylo-SDR Discussion
Subject: [Xylo-SDR] Proof-of-concept successful!
This weekend Bill, KD5TFD, completed
his integration of our Wolfson A/D + Xylo FPGA + USB
interface into PowerSDR.
This proof-of-concepth has been
completely successful and we are eagerly pushing forward to the
next phase of the project.
The screen shot below is of
our 48k 16 bit full duplex sound card running in PowerSDR using an
SDR1000 on 20m
The noise floor of the Wolfson A/D
in this configuration is -140dBm in a 500z bandwidth. The next
steps are to increase the sampling rate to 192kHz and 24 bits.
Bill is also going to implement his
system to overcome the frequency error and drift of the 200MHz Valpey
Fisher oscillator. He is using a GPS 1Hz or 10kHz clock to measure the
frequency of the DDS output and pass this back over the same USB signal
that carries the digital audio. A software routine in PowerSDR will
then compare the actual DDS frequency to the desired frequency and make
the necessary correction in software. If this works OK then he will
look at counting the 200MHz oscillator directly, although picking this
off the SDR1000 hardware is bit more involved than the DDS output hence
the reason for starting with the DDS output.
We are looking at deriving an LVDS
signal from the 200MHz oscillator and if anyone has any suggestions as to
suitable connectors to use with a single LVDS signal then we would
appreciate the information.
There is still plenty of room for
more C++ and FPGA developers if you are interested in assisting with the
project - those willing to lay out PCB's will be especially welcome!
73's Phil.... Vk6APH
FlexRadio mailing list
I fail to see why doing the same thing over and over and getting the
same results every time is insanity: I've almost proved it isn't; only a
few more tests now and I'm sure results will differ this time ...