---------- Forwarded message ----------
From: Karan T. [email protected]
Date: Sat, Jun 29, 2013 at 6:44 PM
Subject: Re: [Discuss-gnuradio] Problem in uhd_fft
To: “[email protected]” [email protected]
Hi Josh,
I am using USRP 1. I am using a sma-bulkhead cable from
Tx_A
of basic tx daughter board and similarly a sma-bulkhead cable from Rx_A
terminal of the Basic Rx daughter board. and then i am connecting a
sma-sma
cable from usrp transmitter to a coupler on powerline cable. Similarly I
am
connecting a sma-sma cable from usrp receiver to another coupler on the
powerline cable.
so in all I am using 2 usrp 1, 2 sma-sma cables, 2 sma-bulkhead cable
and
two couplers. Please let me know if i am not clear with the description.
Thank you.
On Sat, Jun 29, 2013 at 11:24 AM, Josh B. [email protected] wrote:
-31Mhz in the uhd_fft i get a received signal on my fft. why does this
Discuss-gnuradio Info Page
–
Regards
Karan T.
On 06/29/2013 09:14 AM, Karan T. wrote:
terminal of the Basic Rx daughter board. and then i am connecting a sma-sma
cable from usrp transmitter to a coupler on powerline cable. Similarly I am
connecting a sma-sma cable from usrp receiver to another coupler on the
powerline cable.
so in all I am using 2 usrp 1, 2 sma-sma cables, 2 sma-bulkhead cable and
two couplers. Please let me know if i am not clear with the description.
Thank you.
Seems to work OK for me. I used a single USRP1, BasicRX, BasicTX. RXA is
connected to TXA and RXB is connected to TXB. Attached is a GRC flow
graph. Hope that helps.
-josh
Hi Josh,
we tried using the same grc flowgraph and tried transmitting
at
frequencies 33Mhz and 35 Mhz. Though we could see a constant source
output
on the fft, the frequency at which that was occuring was at -31Mhz and
-29Mhz. The output log is shown below for frequency of 33 Mhz. I have
attached a screenshot of my grc too.
enerating: “/home/anrc/Downloads/top_block.py”
Generating: “/home/anrc/Downloads/top_block.py”
Executing: “/home/anrc/Downloads/top_block.py”
linux; GNU C++ version 4.6.3; Boost_104800; UHD_003.004.005-0-unknown
Using Volk machine: sse4_1_64
– Opening a USRP1 device…
– Using FPGA clock rate of 64.000000MHz…
UHD Warning:
The hardware does not support the requested RX frequency:
Target frequency: 33.000000 MHz
Actual frequency: -31.000000 MHz
– Opening a USRP1 device…
– Using FPGA clock rate of 64.000000MHz…
U
Done
On 07/04/2013 01:41 AM, Karan T. wrote:
Hi Josh,
we tried using the same grc flowgraph and tried transmitting at
frequencies 33Mhz and 35 Mhz. Though we could see a constant source output
on the fft, the frequency at which that was occuring was at -31Mhz and
-29Mhz. The output log is shown below for frequency of 33 Mhz. I have
attached a screenshot of my grc too.
That sounds correct. The receive chain performs frequency translation
with a CORDIC running at 64MHz. So -31MHz is an alias of 33MHz and
-29Mhz is an alias of 35MHz
-josh
On 07/04/2013 11:51 PM, Karan T. wrote:
Hi Josh,
can you explain how and why the frequency translation
occurs? secondly when the same basic tx chip is used on a usrp N210,
the translation occurs at 50Mhz and after. So for USRP N210, the
entire range from 0-250 Mhz is represented by alternating between
-50Mhz to +50Mhz. Why is it that way?
The BASIC_RX and LF_RX have no downconversion hardware in them at all.
They are basically just “buffers” for the ADCs. The BASIC_RX has an
analog reponse that starts to fall off at about 250Mhz, which is why
it’s rated to 250Mhz.
In the USRP1/B100/E1XX systems, the sampling clock is at 64MHz by
default. That means the first aliases start to show up at the 1st
Nyquist
frequency of 32Mhz (half of sample rate). Similarly in the N2XX,
which a 100MHz sampling clock, those aliases start to show up at 50Mhz.
My suggestion would be to look into so-called bandpass sampling, and
also, importantly, Nyquist Sampling Theorem.
H
i Marcus,
I got it. It is a case of bandpass sampling. .Thank
you.
Hi Josh,
can you explain how and why the frequency translation
occurs?
secondly when the same basic tx chip is used on a usrp N210, the
translation occurs at 50Mhz and after. So for USRP N210, the entire
range
from 0-250 Mhz is represented by alternating between -50Mhz to +50Mhz.
Why
is it that way?