Hi,
I have an IQ file having a spectrum occupancy of 5kHz, which I want to
replicate to make a wide band spectrum, so when the receiver scans this signal
it should detect multiple spectrum. In GRC I created a flowgraph with resampler
to upsample the IQ from 48kHz to 250kHz. The output of resampler is connected
to usrp. I added another block to multiply with a cosine signal of frequency
5kHz and add to it.
--->| resample|------------------------------------>| adder |---->usrp
|
^
|
|
--------------->| multiplier | |
| cos signal|---------->| (5KHz) |----!
Like this I created multiple blocks with multiplier frequency increased by 5kHz
and added. This when I tried to do the scan it detected, but when tried to
decode individual spectrums, it is not able to decode because of distortions.
Any suggestions on the best way to replicate a spectrum and transmit in USRP
N210 ?
-ben
________________________________
From: Kyeong Su Shin <[email protected]>
Sent: Saturday, March 24, 2018 9:33 PM
To: Benny Alexandar; [email protected]
Subject: RE: [USRP-users] IQ transmission using grc
Hello Ben:
USRP N210 samples at 100MS/s (with an additional 4x interpolation in case of Tx
- making it 400MS/s). The maximum effective sampling rate, however, is
bottlenecked by the connection between the USRP and the PC. The 1Gbps Ethernet
connection can keep up with a 25MS/s 16bit I-Q data stream or a 50MS/s 8bit I-Q
data stream. Faster rate will cause a data loss.
What is important is that the internal sampling rate of the USRP N210 is fixed.
It is always 100MS/s. When you set the effective sampling rate (which is
different from the internal sampling rate of the ADC and DAC) of the USRP in
your code, the data is transferred to the USRP at the configured rate and then
resampled by the FPGA of the USRP to meet the ADC/DAC sampling rate (100MS/s).
This resampler(interpolator) has several restrictions, and restrics the valid
choice of the effective sampling rate (the sampling rate that you are setting
in your software). That is what Marcus explained in the previous e-mail.
So, yes, you can get 50MS/s from your board, but the precision of the data
should be 8 bit instead of 16 bit (which is usually not a good idea).
Furthermore, this does not concern the analog filters installed on the
daughterboard, which may further reduce the usable bandwidth.
Also, yes, at N=200, the effective sampling rate of the board is 500kS/s and
that should work without a problem.
Regards,
Kyeong Su Shin
________________________________
보낸 사람: Benny Alexandar via USRP-users <[email protected]> 대신
USRP-users <[email protected]>
보낸 날짜: 2018년 3월 24일 토요일 오후 2:32:24
받는 사람: Marcus Müller via USRP-users; Marcus D. Leech; Marcus Müller
제목: Re: [USRP-users] IQ transmission using grc
Hi Marcus,
I'm not clear on maximum sample rate support for USRP N210. According to you
>> In case of the N210, these frequencies are integer fractions of 100 MHz
>> i.e. 100 MHz / N, with the restriction that N be an integer 3 < n <=
>> 128 , an even integer 2 < n <= 256 or an integer multiple of 4 <= 512.
Assume I use N an even minimum integer say 2, then the sampling frequency I
can get
on USRP N210 is 100 MHz / 2 = 50 MHz. Is that correct ?
Can USRP sample at such high rates ?
If I need a bandwidth of say 500kHz, from USRP then I need to set N = 200, is
my math correct
and the sample rates to set for usrp ?
-ben
________________________________
From: USRP-users <[email protected]> on behalf of Marcus
Müller via USRP-users <[email protected]>
Sent: Wednesday, March 21, 2018 2:10 AM
To: Marcus D. Leech; [email protected]
Subject: Re: [USRP-users] IQ transmission using grc
Hi ben,
also, no USRP can directly deal with a sampling rate as low as 48 kHz –
you'll first have to resample to a rate that your USRP can deal with.
In case of the N210, these frequencies are integer fractions of 100 MHz
i.e. 100 MHz / N, with the restriction that N be an integer 3 < n <=
128 , an even integer 2 < n <= 256 or an integer multiple of 4 <= 512.
tx_samples_from_file can't resample – you should have been getting UHD
warnings about impossible sampling rates; your IQ file has simply been
played back at a higher rate.
Best regards,
Marcus
On Tue, 2018-03-20 at 12:58 -0400, Marcus D. Leech via USRP-users
wrote:
> On 03/20/2018 12:37 PM, Benny Alexandar via USRP-users wrote:
> > Hi,
> >
> > I have an IQ file sampled at 48kHz and want to transmit through gnu
> > radio. The IQ samples are each 16bit, and stored interleaved in a
> > file
> > ie, IQIQIQIQ... I 16 bit and Q 16bit
> >
> > I tried creating a grc using iShort to Complex block and send to
> > USRP sink block (usrp n210), but the signal received is distorted.
> > Do I need to convert the short values into float -1.0 to +1.0
> > before transmission. Please help in resolving it.
> >
> > I want to use it only through grc and not to use
> > tx_samples_from_file which does the same.
> >
> > -ben
> >
> You'll need to scale your samples into {-1.0,1.0}
>
>
>
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