I forgot to note a VERY IMPORTANT POINT, you must REBOOT, so the changes made to the limits.conf file allow the user to make changes to process priority.

I proof read my document many times before I posted it on eHam, but this error got past me.

I apologize for any inconvenience.

73



I want to add these supporting links too:

http://www.ibm.com/developerworks/linux/library/l-lpic1-v3-103-6/

http://en.wikipedia.org/wiki/Real-time_computing#Real-time_in_Digital_Signal_Processing

https://wiki.archlinux.org/index.php/Realtime_process_management

Fldigi is installed to run in Ubuntu with a "normal" process priority. This setting can be observed in the "System Monitor" application that is part of the Ubuntu operating System by selecting the "processes tab". Use the "view" setting to select "all processes" if you wish to see CPU load of all the processes running on your system.

Another, very interesting way to view processing load is to use the Linux command "TOP" in a terminal window. Load Fldigi, and decode signals and observed the results.

I change Fldigi process priority level from "normal" to "very high" for improved digital mode decoding performance on my computer system.

Process priority can only be  changed by a user as "root", but you can make a very simple edit to the "limits.conf" file as root to give a non-root user permission to change the process priority of a application (fldigi).

Method:

#1 Open a Terminal

#2 Become "root"   Type:  sudo su  (press enter) - (notice the space between sudo and su)

#3 Enter your password

#4 Type this at the command prompt (your prompt should look something like root@computername:/home/your-home-directory#)

   nano /etc/security/limits.conf   (press enter) - (nano is a text editor)

#5 Scroll down to the bottom of the limits.conf file using the down arrow key. Go to the very bottom, past the line that states "# end of file".

#6 Add this to the limits.conf file:


   username     -     nice     -20            (user name is YOUR sign-on user name that you use with your password to log on to your system). Notice the dashes!
                                                             Notice the examples above the "# end of file line". Line up your entry to match those examples.

#7 Save your entries to the file by pressing:  Ctrl  O   then press "Enter"    (Control and the letter O).

#8  Exit Nano:   Press Ctrl X   to exit.

#9 Type exit (Press enter) to exit root.

IF YOU MAKE A MISTAKE, CLOSE THE TEXT EDITOR (NANO) BY PRESSING "Ctrl and X" AND NO CHANGES WILL BE MADE. THEN JUST START OVER AGAIN.

#10 How to make the Process Priority change work:

    When you boot into your graphic user interface, start fldigi, and then open "System Monitor", and then click on the processes tab and find Fldigi listed among all the current system processes running. Highlight fldigi and click on it. Then right click and select "Change Priority", and select "Very High". That's it!

   But... This change will only last for this one session, when you reboot, Fldigi will revert back to normal process priority. You must use the System Monitor application to change Fldigi process priority each time you start your computer. It's easy! Again... Start Fldigi, start System Monitor, change Fldigi process priority to "Very High". Done! I would suggest you close system monitor, because it is a high load resource application. Use the Linux command "top" in a terminal window to view processes in the order of CPU usage. This information can be used to understand decoding performance on YOUR system.

Real-time process have demanding process scheduling requirements, and such process should never be blocked by lower priority processes, they should have short response time, and these response times should have a minimum variance. Common real-time programs are applications that collect continuous streams of data and process that data in real time, like Fldigi does.

I have read posts that Fldigi has very high resource requirements. This is simply not true! Compared to what other digital mode application? Any application that is sampling a data stream, and is doing fast Fourier transform needs CPU cycles. If you compare a digital mode decoder with a waterfall, and a decoder without a waterfall, the decoder without a waterfall will use less percentage of the CPU cycles. Compare Fldigi, and Xorg (video driver) with, and without the waterfall with the "top" command in a terminal. Also, when it is decoding, and not decoding.

Lastly... A word of caution. Just change the process priority of Fldigi only. You can degrade your system performance, or make your Linux system unstable, if you make process priority unbalanced.

My Linux system never, ever crashes.  My research, experimentation, and monitoring of this adjustment to Fldigi process priority has improved the performance of Fldigi on my computer. The antenna, the transceiver, the interface, the data stream... processing.

Make Fldigi "boss" app!

73

A link to a good 2 part article from Test and Measurement World, "Windowing Funtions Improve FFT Results". To quote a reader comment, it is a "extremely well written article for explaining a very hard concept".

Use these links. The part #2 link within the part #1 article is a dead link "page not found".

http://www.tmworld.com/electronics-news/4383713/Windowing-Functions-Improve-FFT-Results-Part-I

http://www.tmworld.com/electronics-news/4386852/Windowing-Functions-Improve-FFT-Results-Part-II

Just to share some information with the eHam community.

also see...

http://en.wikipedia.org/wiki/Window_function 

http://en.wikipedia.org/wiki/Fourier_transform

http://en.wikipedia.org/wiki/Fast_Fourier_transform

When the automatic gain control circuit reduces audio gain, tweaking the fast fourier trasform processing could greatly improve your signal processing in a lot of receive situations.

I always have the fldigi confirguraton window open to make real-time adjustments to the FFT processing as receive conditions vary. The "Blackman" fft is the default fast fourier transfrom prefilter window function in fldigi, but I tend to use "Rectangular", and then maybe "Hanning" for my fft window, but I have used all of the fft prefilters windows to tweak my signal processing based on receive conditions.

The audio sample rate, and converter type is important too. Use the Linux system monitor, or Windows task manger "performance tab" to determine CPU load. The "best sinc interpolator" can cause 100% CPU load in some old cpu processor types. Even my modern day intel atom processor can see very high load with the selection of the wrong interpolator type. I use the "fastest", with a high sample rate (96000 bps) via portaudio in linux.

I use the FFT signal line display in my waterfall window to reduce cpu load, and use the signal browser to select signals. You can get a "feel" for your fft latency rate, and gain a better understanding of your computers performance as it applies to the fft algorithm processing power.

Determine if your FFT Latency Adjustment is correct. Again, "4" is default, but I tend to use "2". I have many times used 6 or 7 based on fft processing performance during varying signal conditions, and the fft prefilter window I have selected.

The fast fourier transform algorithm is very powerful, and can be adjusted to meet the varying signal conditions that a digital mode amateur radio operator encounters, and used as a tool to overcome some of the limitations of the transceiver. FFT is the most important feature of fldigi, and with perfect adjustment, can help greatly if you do not have the best digital mode transceiver. Learning FFT processing adjustments, and optimizing FFT window function can help decoding significantly.

In PSK the computer, and software package (FFT) are just as important as the transceiver, and antenna. A powerful cpu, and a well adjusted fft window can decode a weak signal when it is reduced by AGC.

Practice adjusting fft with no filter, just the audio input, and then apply passband techniques when you have mastered FFT processing.

I have a Icom 718. It has no agc control at all. I have observed that perfect adjustments to Fast Fourier Transform have helped a lot in using my transceiver in PSK.

Fldigi version 3.21.50 is available in the Ubuntu "Quantal" repository. It is a maintenance release update. Mostly likely minor bug fixes, and other improvements made by the developer(s). It can be quickly installed by downloading from a ubuntu quantal mirror, and then use Ubuntu Software Center to install.

A 2-3 minute procedure will get you the latest and greatest version of fldigi.

Check out this eham digital forum posting for tips on how to install fldigi via Ubuntu Software Center after downloading the fldigi package from a mirror.

http://www.eham.net/ehamforum/smf/index.php/topic,84364.0.html

I did notice that the mit.edu server was 404 (down), so I used rit.edu. The mit.edu server might be fixed when this is posted on the eham forum.

A edit to my posting above....

There is a dead link due to a typo... should be just:       packages.ubuntu.com/

NOT  www.packages.ubuntu.com  (dead link)

Sorry about that.

I personally would never use the upgrade path to use a new version of any Linux distribution. I always do a clean install. It is very common for people to post reports of upgrade issues in the Ubuntu forums. I guess it works for some.

My normal install routine is to use the gparted live CD to zero out/wipe a few gigabytes of the hard drive.

Command in the "root terminal":   dd if=/dev/zero of=/dev/sda bs=1M

 then ctrl c to stop the process, after a minute or two.

Then I use Ubuntu live CD to install. I press enter when I see the Ubuntu icon/ keyboard, and select "install". I also tab for a custom command namely video=LVDS-1:d for a resolution issue.

I keep my system lean, and fresh... Ubuntu is a very stable platform for me, and easy to update the packages. Which I do frequently.

I have also used a fresh install to correct problems after updates. I did that recently when a intel video driver update caused a daemon problem.

I also run Firefox without plugins, and use Google chrome for flash when needed, as there will be no new updates for flash in Linux, just 5 years of security updates only from Adobe. Works well for me. Google has licensed flash for there use in Linux, and it is now built into Chrome. Google "flash player about" or "linux flash" for more info.

I've gotten used to unity.

My 78 year old Mother uses Ubuntu, and likes it!

Assuming you are using Ubuntu 12.04 (Precise), you can just point and click to install FLDIGI using Ubuntu Software Center.

There are 2 methods I use, and both are easy. The methods are essentially the same, but install different versions of the FLDIGI software package. I use method #2 mostly.


Method #1:

The first method will install the current software package (FLDIGI) available within the current release of Ubuntu. As I type this reply to your question, that would be Ubuntu version 12.04 (Precise), and the current FLDIGI package available for installation is FLDIGI (3.21.38-1).

#1 Click on "Ubuntu Software Center"

#2 Search with Ubuntu Software Center for the application "fldigi"  ( the box - upper with magnifier glass symbol ).

#3 When the search results are displayed that show the package/application "fldigi" - click install - be patient - the installation is slow - about 1 to 2 minutes, and there is some, but not a lot of feedback from Ubuntu about the installation process. Ubuntu has to install the package (fldigi) and it's required dependences.

#4 Setup - Configure the fldigi application to meet your digital mode hardware requirements.


Method #2:

This is a very easy method to install the latest and greatest version release of FLDIGI. Again... as I type this reply to you, that would be version fldigi (3.21.48-1). It seems that the developers of fldigi fix bugs brought to their attention in a VERY timing manner. FLDIGI is a very well maintained Linux amateur radio application. The work is done by a core group of Linux software developer hams working together to support the amateur radio community.

#1 Google search "Ubuntu packages" - the search results will reveal a link to www.packages.Ubuntu.com - click on that link. You will see a page "browse through the list of packages". Find the package set under "quantal" ( this is Ubuntu version 12.10 it is not released yet ).

  Find the package group "HAM RADIO".
  Find fldigi (3.21.48-1 [universe] - click on that link.

  Scroll to the bottom of the page... "Download fldigi"

  Click on the architecture you use amd64 (64bit) or i386 (32bit). This will be up the actual download page (mirrors). Click a a mirror link and select "SAVE" the file. I use "North    America" and "ubunut.media.mit.edu" sometimes i use "rit.edu" also.

This will download the fldigi file to your HOME directory DOWNLOADS folder. When the download is complete - close your web browser, and open the file manager Nautilus, and locate the file you just downloaded in the Home directory Downloads folder... the file should be either : fldigi_3.21.48-1_amd64.deb  or  fldigi_3.21.48-1_i386.deb  again, it depends on the computer architecture you are using.

Now to install FLDIGI - Right Click and select "Open with Ubuntu Software Center".  Like I stated before there is not a whole lot of feedback during the install process ... SO BE PATIENT! It will install!

#2 Setup - Configure the fldigi application to meet your digital mode hardware requirements. Enjoy.

It seems like a lot, but this method take 15 to 20 seconds to implement.

This method should be able to be used for future Ubuntu and Fldigi releases.

It works well for me.

With a old spare computer,and a free high tech operating system like Linux, and a free digital mode software application like fldigi, I spend my money on other ham gear. Thank you fldigi developers very much.

I hope this helps you.  N1ISA

Why would you want to block direct current when using a lightening coaxial protector?

I want lightening pulse protection, AND static drain protection. Would a DC block unit do this better than other designed types?

Is a DC pass through device mostly used for a bias-T type situation?

I've been researching this via the web, but I can not develop a clear understanding of these 2 different design types, and how to apply them my protection requirements.

Thank you.