I have a few queries regarding some of the options for improving the
performance of the XCVR2450 + N210.
The N210 can offer 50MSPS with 8 bit I&Q samples or 25MSPS with 16bit
1&Q.
If using 16 bit I &Q samples, I’d just leave the UHD input block with
“Complex int 16”.
How do I implement 8 bit I&Q (e.g. what input type do I use? and if it
is
16bit… do I have to decimate my signal in half or something? I don’t
need
to do anything to the hardware or firmware do I?)
After reading further, I see that the N210 can apparently offer
100MSPS
total host bandwidth with 8bit!
These seems to imply that 50MSPS refers to both transmitting and
receiving
simulatneously
Does this mean that if i’m only transmitting that I can thus use 100MSPS
some how?
How do I change/set ports on the XCVR2450 or check which i’m using:
From what I read with the instructions, one shouldn’t transmit unless
they
have an antenna or 50ohm terminator attached or it will damage the
device?
I’m transmitting out of port J2 and have a terminator on J1. When I
swap…
I seem to get lower power signals out of port J1?
I haven’t (as far as i’m aware, done anything to change the settings…
or
port preference)
Does this mean that it transmits out of both ports, and one of mine is
damaged?
Is it true that port J1 is the default port? in which case why are my
signals coming out of both?
Do both ports offer transmit and receive, or is one port set to one
function and the other port the other…
Sorry for the basic question but i’ve found conflicting info on the net
regarding this, and still very much in the learning phase.
For 8 bit you change the wire format parameter of the UHD Source and
Sink from “automatic” to “sc8”. This is one of the options you get when
double clicking the Source/Sink in GRC. Changing the output type of the
block in GRC has no effect on the wire format. No modification to
hardware or firmware necessary. Also, decimation would lower the
bandwidth but, once again, all you have to do is change the option.
First off, the XCVR2450 is half duplex, so it can only transmit or
receive at a time, not both. Maybe check out the SBX daughterboard if
you want to do both (depends on your application, there are a few full
duplex daughterboards in the ism band.) Also, remember that Ethernet has
discrete TX and RX lines and each line is limited to roughly 50MSPS at
8bit, so you cant only transmit or only receive at 100MSPS.
It’s always a good idea to terminate a transmitter as high power
reflections could damage your amplifier. It’s been a while since I used
the XCVR and I can’t remember exactly how it divided its ports. Not sure
whether (since its half duplex) if it used the same port for both tx and
rx by default or if they default to separate ports. You can definitely
select the port when only transmitting or receiving. There is an antenna
option in the usrp sink.source blocks. I’ve never used that option
myself though so I’m not sure what type of input it expect. An integer
would be my best guess so maybe start at 0 and see what you observe. If
you wanted to transmit and receive on the same port you would have to
stream tag the tx stream and set both blocks (sink and source) for the
same port. The device defaults to receive and when it receives a tx_sob
alongside the transmit signal it will switch to tx. When it receives a
tx_eob, it will switch back to rx. Switching time for the xcvr is in the
microsecond range. If the signals you are observing on J1 are very low
power compared to those on J2, this could be poor isolation. The rf
switch on the two output ports should provide 30dB of isolation. It’s
possible isolation on the board itself might cause some leakage too.