ematlis | 30 Jul 22:14 2014
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increasing output power from lftx with resistor mod gives saturated output

Hello-

I have attempted to increase the output power from my Rev 2.2 LFTX as per instructions from Matt Ettus on this
list dated Aug 3 2013 in which he suggests reducing the values of resistors R3 and R5, but I am seeing a
clipped output at peak values much less than expected. 

Using the ettus.com LFTX schematic as a guide, I left the resistors on the board untouched, but soldered
wires to either side of R3 and R5 to add additional resistors in parallel.  My first attempt was with
resistors of value 220 ohms; I figured this would about halve the value at R3 and R5 which are originally 225
ohms.  I do see some increase in output power, but very minimal.  Specifically, whereas before I was
observing 1 V P-P, or about 2.5 milli-watts on an oscilloscope that is 50-ohm DC coupled,  I am now seeing
1.34 V P-P, or about 4.6 milli-watts with a 1 kHz sine-wave.  To obtain this without clipping I had to
reduce the amplitude on the USRP sink block from 1 to about .77, othwerwise the tops of the sinusoids
flatten anywhere above the 1.34 V P-P level.  So I appear to be saturated.

I am using a USRP1 Rev. 3.  I verified that the LFTX output op-amp in question is supplied with +/- 3.3 volts,
so I don't see why it is clipping at half of this.

I am hoping to use the LFTX in an HF Ham radio application.  I have mini-circuits ZHL-1A TX pre-amplifier
for this purpose, but was hoping to obtain a little more output from the LFTX than I am currently getting to
drive the ZHL-1A.  Any thoughts?

Thanks!

Eric
Martin Braun | 30 Jul 21:52 2014

Re: Spectrum sensing Simulation Only

Tadilo,

please stick to the mailing list.

On 07/30/2014 08:23 PM, Bogale, Tadilo Endeshaw wrote:
> Hello Martin 
> 
> Thank you for the help. I try to run "specest_noisy_sinusoid_mtm.py" (Python script is also okey for me).
However it does not run "it says no module specest".

Did you install gr-specest?

> 
> My goal is is to write a simple python or gnuradio code to perform the following task 

That's really simple. In gr-specest, the "Welch" blocks pretty much do
that. Even without, you can easily click that together in GRC.

M
> 
> I have the following variables
> 
> NFFT=1024
> Nav=512
> ampl=1
> seed=1
> Sampling_rate= 10k
> 
> 1. Generate any real time signal (This could be done by using "gr.noise_source_f (gr.GR_GAUSSIAN, ampl, seed1)).
> 
(Continue reading)

ematlis | 30 Jul 21:38 2014
Picon

increasing output power from lftx with resistor mod gives saturated output

Hello-

I have attempted to increase the output power from my Rev 2.2 LFTX as per instructions from Matt Ettus on this
list dated Aug 3 2013 in which he suggests reducing the values of resistors R3 and R5, but I am seeing a
clipped output at peak values much less than expected.  

Using the ettus.com LFTX schematic as a guide, I left the resistors on the board untouched, but soldered
wires to either side of R3 and R5 to add additional resistors in parallel.  My first attempt was with
resistors of value 220 ohms; I figured this would about halve the value at R3 and R5 which are originally 225
ohms.  I do see some increase in output power, but very minimal.  Specifically, whereas before I was
observing 1 V P-P, or about 2.5 milli-watts on an oscilloscope that is 50-ohm DC coupled,  I am now seeing
1.34 V P-P, or about 4.6 milli-watts with a 1 kHz sine-wave.  To obtain this without clipping I had to reduce
the amplitude on the USRP sink block from 1 to about .77, othwerwise the tops of the sinusoids flatten
anywhere above the 1.34 V P-P level.  So I appear to be satura
 ted. 

I am using a USRP1 Rev. 3.  I verified that the LFTX output op-amp in question is supplied with +/- 3.3 volts, so
I don't see why it is clipping at half of this.

I am hoping to use the LFTX in an HF Ham radio application.  I have mini-circuits ZHL-1A TX pre-amplifier for
this purpose, but was hoping to obtain a little more output from the LFTX than I am currently getting to
drive the ZHL-1A.  Any thoughts?

Thanks!

Eric
Bogale, Tadilo Endeshaw | 30 Jul 20:48 2014
Picon

Re Spectrum sensing Simulation Only

Hello Martin

Thank you for the help. I try to run "specest_noisy_sinusoid_mtm.py" (Python script is also okey for me).
However it does not run "it says no module specest". 

By the way I am using windows 8 OS.

My goal is is to write a simple python or gnuradio code to perform the following task

I have the following variables

NFFT=1024
Nav=512
ampl=1
seed=1
Sampling_rate= 10k

1. Generate any real time signal (This could be done by using "gr.noise_source_f (gr.GR_GAUSSIAN, ampl, seed1)).

2. Insert throttle to control the sampling rate (i.e., gr.throttle(1, Sampling_rate))

3. Compute the FFT (even without windowing) (i.e., NFFT samples at a time)

    Let me assume that after I compute FFT and I got an "x" vector of size NFFT

4. Compute the square magnitude of x (This could be done by using gr.complex_to_mag_squared(NFFT))

i.e., in matlab y=abs(x).^2

4. sum the first and second Nav samples
(Continue reading)

Daniele Nicolodi | 30 Jul 18:42 2014
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Filter in rational resampler

Hello,

I was studying the code of the rational resampler block in
gnuradio/gr-filter/pythoin/rational_resampler.py and I have a doubt
about the low pass filter generated by the design_filter() function.

It seems that the generated filter does not take into account the
decimation factor. Is that correct? I don't see how this may result in
the correct anti-aliasing filter when it is applied by
rational_resampler_base_xxx.

Can someone point me to a relevant explanation?

Thanks a lot. Cheers,
Daniele
Daniele Nicolodi | 30 Jul 13:50 2014
Picon

Messages and flow-graph termination

Hello,

as soon as I introduce a pair of block publishing and consuming
messages, the GNURadio scheduler (version 3.7.2) does not terminate the
execution of the flow-graph when the stream sources signal the end of
the stream.

This is also reflected in how the test case qa_python_message_passing
checks for the termination of the execution.

Is this by design, is it a known limitation, or is it a bug?

Cheers,
Daniele
xianda | 30 Jul 10:57 2014

ofdm channel estimation

Hi Martin:
                Greeting from xd.Thank you so much for your example tx_ofdm.grc and rx_ofdm.grc.I want to ask a question about channel estimation.And I know that the channel estimate is on a tag.But I want to make some changes on your example.So I just want to ask whether my understanding is right or not.
               I know the rx_ofdm include "header stream" and "payload stream".In the "payload stream",if i denote the data come from FFT block "rx_data".
               channel=rx_data/tx_data
              Is it right?Is my understanding right?Thank you.
Best regards,
xd


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Nguyễn Văn Lý | 30 Jul 10:44 2014
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What do Packet Encoder and Packet Decoder do?

Hi all,

Can anyone tell me what do Packet Encoder and Packet Decoder blocks do? and it would be great if you can give me some example :-) 
Thanks in advance

Van-Ly

Van-Ly Nguyen,
Signals and Systems of Laboratory - SSL  
Faculty of Electronics and Telecommunications - FET         
University of Engineering and Technology - UET      
Vietnam National University, Hanoi - VNU  

Tel: (+84) 978 819 406

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xianda | 30 Jul 03:59 2014

tx_ofdm.grc start_of_burst end_of_burst

Hi all:
         I know a packet in the example tx_ofdm.grc include a preamble,a header,the payload and crc value.Recently I have used the UHD API to send packet.And I want to know whether the tx_ofdm.grc add start_of_burst and end_of_burst automatically.Namely,need I add start_of_burst at the beginning of every packet and add end_of_burst at the end of every packet?
        Thank you very much.
Best regards,
xd


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Stefan Oltmanns | 29 Jul 23:53 2014
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Port flowgraph from Python to C++

Hello,
I was able to create a flowgraph in GRC to demodulate a signal
(low-frequency battery telegram of wireless microphones). Now I started
to port the generated code from Python to C++.
I had to realize that some blocks are Python-only, like the FM
Demodulator. I was able to rebuild the FM Demodulator in C++, for one
exception: The FM demodulator uses optfir, which is implemented in
Python, so it cannot be used in C++. So I replaced it with firdes (I
noticed the parameter difference in transition band end and transition
band width).
Another thing is that the Frequency-Xlating-Filter uses a complex
lowpass, but in C++ I could only find a complex band-pass, so I used a
band-pass with lower frequency 0, is that the same?

Also it works, the signal is a lot noisier and the result cannot be
decoded in many cases. I think the reason are the different filters.
Could that be the reason?
As I understood, both optfir and firdes create just a bunch of numbers
and that´s it. As my program is not going change the filter parameters
they could be hardcoded in my program, right?

Best regards
Stefan

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Bogale, Tadilo Endeshaw | 29 Jul 21:34 2014
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Spectrum sensing Simulation Only

Hello Everyone

I am a new to gnuradio. I would like to do simulation of spectrum sensing (Simple energy detector with single
band only).

Normally I have seen "usrp_spectrum_sense.py". However, that is written for USRP (and not easy to
understand and modify it). Actually I have a difficulty in computing average and display it continuously
in a graphical user interface. 

See also my grc and corresponding python code (The vector sinc block is not correct).

Any help is appreciated.

Thanks,
---
Tadilo Endeshaw, PhD
 Postdoctoral Researcher
 Institut National de recherche Scientifique
 Centre Energie Matriaux Telecommunications
 Place Bonaventure,
 800 de la Gauchetiere Ouest, Suite 6900
 H5A 1K6
 Montreal, QC
 Canada
 E-mail : tadilo.bogale <at> emt.inrs.ca
          tadilo291 <at> yahoo.com (private) 
Personal home page: https://sites.google.com/site/tadilomypage/
Attachment (SimpleEnergyDetector5.grc): application/octet-stream, 10 KiB
Attachment (top_block.py): text/x-python, 3194 bytes
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