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View all threadsRe: [USRP-users] USRP-users Digest, Vol 50, Issue 3
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Today's Topics:
1. Re: Frequency translation works differently on N210 and B210.
(Urban Hakansson)
2. Re: Frequency translation works differently on N210 and B210.
(mleech@ripnet.com)
3. Re: Frequency translation works differently on N210 and B210.
(Urban Hakansson)
4. Re: UHD Related (Michael West)
5. Help building UHD...? (Robert McIntyre)
6. Re: rx_samples_to_file issue (gsmandvoip)
7. Re: B210 UHD Error (Ralph A. Schmid, dk5ras)
8. Re: rx_samples_to_file issue (Peter Witkowski)
9. Re: rx_samples_to_file issue (mleech@ripnet.com)
- Re: rx_samples_to_file issue (Marcus M?ller)
- Re: rx_samples_to_file issue (Peter Witkowski)
Message: 1
Date: Thu, 2 Oct 2014 14:08:10 -0400 (EDT)
From: Urban Hakansson uhakansson@tecore.com
To: Ian Buckley ianb@ionconcepts.com
Cc: usrp-users@lists.ettus.com
Subject: Re: [USRP-users] Frequency translation works differently on
N210 and B210.
Message-ID: 878459104.1456258.1412273290903.JavaMail.root@tecore.com
Content-Type: text/plain; charset="utf-8"
Ian,
I confirmed it on my B210. You are absolutely correct. For Fs = 1.66667
MHz (5MHz/3), the alias component at fc-(Fs-f) starts to show up when f
approaches Fs/4 (~416KHz), and grows stronger the closer the frequency came
to the Nyquist frequency Fs/2(833.33kHz).
However I ran the same test on the N210 for Fs = 6.25 MHz (100MHz/16) and
the results were not good. First, there is No UHD warning about CIC rolloff
or using odd interpolation. I take it to mean that only the half-band
filters in the FPGA are used, and I expected only to see the desired
sinsoid at fc+f.
Case 1) Fs = 6.25 MHz. fc = 800MHz, f = 2.4MHz
The spectrum analyzer clearly shows two components besides the LO, at
fc-f = 797.6MHz
fc+f = 802.4 MHz.
I swept f from 0Hz and upwards and saw two components at fc-f and fc+f.
The fc-f replica is ~15.5 dB below fc+f for f = 2.4MHz.
Please see attached image of the spectrum analyzer, N210_Fs6.25M_f2.4M.jpg.
Case 2) Fs = 6.25 MHz. fc = 800MHz, f = 2.8MHz.
As I increase f and approach the Nyquist frequency 3.125 MHz I see the
same thing happen that I observe on the B210.
The spectrum analyzer clearly shows four components besides the LO, at
fc-(Fs-f) = 796.55MHz
fc-f = 797.2MHz
fc+f = 802.8MHz
fc+(Fs-f) = 803.45MHz
See attached image of the spectrum analyzer, N210_Fs6.25M_f2.8M.jpg.
So in conclusion, I see two undesired phenomena on my N210 + SBX
daughterboard Rev 5.1.
-
I see a strong replica at fc-f in addition to the desired signal at
fc+f for all frequencies f from 0 to Fs/2 Hz. -
I see two aliases show up at fc +/-(Fs-f) as the the frequency of the
complex exponential approaches the Nyquist frequency.
Could I be mismatching the fpga version(FPGA Version: 10.1), firmware
version (FW Version: 12.4), and UHD driver
version(UHD_003.007.001-0-unknown)?
Regards,
Urban
----- Original Message -----
From: "Ian Buckley" ianb@ionconcepts.com
To: "Urban Hakansson" uhakansson@tecore.com
Cc: "Marcus D. Leech" mleech@ripnet.com, usrp-users@lists.ettus.com
Sent: Thursday, October 2, 2014 1:32:58 AM
Subject: Re: [USRP-users] Frequency translation works differently on N210
and B210.
What you are seeing is exactly as sampling theory would predict.
Your fc+f signal shows up on your spectrum analyzer at 800.625Mhz
(Remember your 750kHz became 750*1.6666/2.000)
Your "fc-f" image is not at fc-f (which would be 799.375MHz) but at
1.66666Mhz - 0.625Mhz = 798.95Mhz
You see the alias so prominently because the pure CIC filter has terrible
stop band rejection which is why it's largely unsuitable as a generic
interpolation filter on it's own.
Sweep you CW frequency slowly and watch the direction the image appears
from?this is your clue where it's coming from, and a good practical
technique when looking at real world signals and there unexpected
by-products.
If you select peak hold on your spectrum analyzer and sweep the frequency
you will plot the frequency response of the CIC filter. Try it with sample
rate 2.5MHz and 1.25MHz and see the response of the small half band filter
and then the cascaded half band filters
Now if you turn up the gain some more you will see a true "fc-f" signal,
probably some 40-50db below your main signal and this will be due to the
residual IQ imbalance present in real world direct conversion receivers.
-Ian
On Oct 1, 2014, at 12:45 PM, Urban Hakansson uhakansson@tecore.com
wrote:
Yes, I deliberately requested a sample rate that would force the use of
the FPGA CIC filters. Fs = 1.666667 MHz is fine. I expected roll-off but I
did not expect the replica at fc-f. The CIC filters should not introduce
that kind of error, at least that is my understanding.
----- Original Message -----FW Version: 12.4
From: "Ian Buckley" ianb@ionconcepts.com
To: "Urban Hakansson" uhakansson@tecore.com
Cc: "Marcus D. Leech" mleech@ripnet.com, usrp-users@lists.ettus.com
Sent: Wednesday, October 1, 2014 2:53:04 PM
Subject: Re: [USRP-users] Frequency translation works differently on
N210 and B210.
Did you note the warnings that this generates? The USRP's can not
perform fractional rate conversions. Your sample rate was coerced to be
compatible with a 5MHz master clock rate and up sampling was pure CIC
filter based which has less than ideal spectra:
UHD Warning:
The requested interpolation is odd; the user should expect CIC
rolloff.
Select an even interpolation to ensure that a halfband filter is
enabled.
interpolation = dsp_rate/samp_rate -> 3 = (5.000000 MHz)/(2.000000
MHz)
UHD Warning:
The hardware does not support the requested TX sample rate:
Target sample rate: 2.000000 MSps
Actual sample rate: 1.666667 MSps
UHD Warning:
The requested interpolation is odd; the user should expect CIC
rolloff.
Select an even interpolation to ensure that a halfband filter is
enabled.
interpolation = dsp_rate/samp_rate -> 3 = (5.000000 MHz)/(2.000000
MHz)
UHD Warning:
The hardware does not support the requested TX sample rate:
Target sample rate: 2.000000 MSps
Actual sample rate: 1.666667 MSps
On Oct 1, 2014, at 11:41 AM, Urban Hakansson uhakansson@tecore.com
wrote:
Ian,
Thanks for taking a look at this problem. There is no sample rate
conversion 2MHz->5MHz taking place. I executed the same flow graph for two
different sample rates. The master clock rate was set to 5 MHz in both
cases.
Case 1) The sample rate was set to 5 MHz (equal to the master clock
rate).
Case 2) The sample rate was set to 2 MHz (not equal to the master clock
rate).
Urban
----- Original Message -----
From: "Ian Buckley" ianb@ionconcepts.com
To: "Urban Hakansson" uhakansson@tecore.com
Cc: "Marcus D. Leech" mleech@ripnet.com, usrp-users@lists.ettus.com
Sent: Wednesday, October 1, 2014 2:20:34 PM
Subject: Re: [USRP-users] Frequency translation works differently on
N210 and B210.
Urban, a quick question?I just glanced at your flow graph, it's very
simple?I'm wondering where did the sample rate conversion occur
(2MHz->5MHz) in your example 2) quoted below? There is no re-sampling
block instantiated in your flow graph.
On Oct 1, 2014, at 10:33 AM, Urban Hakansson via USRP-users <
usrp-users@lists.ettus.com> wrote:
First, thank you for responding so promptly. I attach the Gnu Radio
flow-graph and the generated python script. It contains two USRP sink
objects, one configured for the B210 and the other for the N210. FYI, I use
GnuRadio companinion 3.7.1.1 and 3.7.2.2.
I also attach two example images from the spectrum analyzer looking at
the spectrum from the B210.
Image 1) B210 master clock rate = 5MHz, Sampling rate = 5 MHz,
frequency of complex exponential = 1.2 MHz, center frequency = 800MHz.
No replica at fc-f. As expected.
Image 2) B210 master clock rate = 5MHz, Sampling rate = 2 MHz,
frequency of complex exponential = 750 kHz, center frequency = 800MHz.
Replica at fc-f.
The result from the N210 is a replica at fc-f as well so I don't
include a image.
Regards,
Urban Hakansson
----- Original Message -----
From: "Marcus D. Leech via USRP-users" usrp-users@lists.ettus.com
To: usrp-users@lists.ettus.com
Sent: Tuesday, September 30, 2014 8:11:34 PM
Subject: Re: [USRP-users] Frequency translation works differently on
N210 and B210.
On 09/30/2014 06:20 PM, Urban Hakansson via USRP-users wrote:
Hi everybody,
I have a problem. I include below 1) General information, 2)
Introduction to my problem 3) Detailed description of my problem.
General background information about my environment:
Fedora 17 Linux; GNU C++ version 4.7.0 20120507 (Red Hat 4.7.0-5);
Boost_104800; UHD_003.007.001-0-unknown
N210 informationfrom uhd_usrp_probe:
| Device: USRP2 / N-Series Device
| _____________________________________________________
| /
| | Mboard: N210r4
| | hardware: 2577
| | mac-addr: 00:80:2f:0a:e6:15
| | ip-addr: 192.168.2.199
| | subnet: 255.255.255.255
| | gateway: 255.255.255.255
| | gpsdo: none
| | serial: F4A09C
| | FW Version: 12.4
| | FPGA Version: 10.1
B210 information from uhd_usrp_probe:
| Device: B-Series Device
| _____________________________________________________
| /
| | Mboard: B210
| | revision: 4
| | product: 2
| | serial: F571B5
| | FW Version: 4.0
| | FPGA Version: 3.0
Introduction/background: It is my understanding that outputting a
real-valued baseband signal x(t) = asin(2pift) on an RF carrier fc
should result in two components at fc+f and fc-f, but outputting a
complex-valued baseband signal x(t) = exp(2pif*t) should only result in
an fc+f component. The complex exponential can be used for frequency
translation but is causing me serious problems on the N210 + SBX
daughterboard.
Detailed Problem Description: Using GnuRadio I output a simple
baseband complex exponential at frequency +f centered at the RF center
frequency fc. Now on the N210 in addition to the sinusoid at fc+f there is
a unexpected replica at fc-f about 13-14 dB below fc+f. When I run the same
script on the B210 and set master clock rate equal to the sample clock
rate, I only see the desired frequency component at fc+f. There is no
replica at fc-f as in the case of the N210. This is the correct behaviour
as I understand it. However, if I don't set the master clock rate equal to
the sample rate on the B210 I do get the undesired replica at fc-f 13-14 dB
below the signal at fc+f just as I did on the N210.
Why does it only work if the master clock rate is set equal to the
sample clock rate on the B210? I have read somewhere on the mailing list
that the FPGA including CIC and HB filters are bypassed in this case.
Question: How can I output a simple complex-valued baseband signal
x(t) = exp(2pif*t) on an RF carrier fc on the N210 and only get an fc+f
component so I can use this mechanism to perform frequency translation?
Thanks for you consideration.
Regards,
Urban Hakansson
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Could you perhaps share your Gnu Radio flow-graph with us? It would
help in seeing where your problems might originate.
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you.grc>py>specA_Fs2MHz_750kHz.JPG>specA_Fs5MHz_f1.2MHz.JPG>_______________________________________________
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notify the sender by return e-mail (or sysadmin@tecore.com), then delete
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legally protected information, and is intended exclusively for the intended
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retransmit it in any form. If you are not the intended recipient or
otherwise have received this by mistake, please immediately notify the
sender by return e-mail (or sysadmin@tecore.com), then delete the message
in its entirety. Thank you.
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legally protected information, and is intended exclusively for the intended
recipient. If you are not the intended recipient (even if the e-mail
address above is yours), you may not review, store, use, copy, disclose or
retransmit it in any form. If you are not the intended recipient or
otherwise have received this by mistake, please immediately notify the
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