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Showing posts from 2016

The Filter Works!

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I don't usually blow my own trumpet. I usually use somebody else's But I can't keep this to myself.
The low pass filter works and works well. Of course it helps to have an LC meter to measure the coils. A bit tricky for the ones less than a microhenry but it does give a close approximation.
It also helps to be able to "sweep" the filter when finished. This I did with an HP spectrum analyser and tracking generator. In the 'old days' [last century] I would plot the response on a XY plotter. To send it out to others would need photo copying. Now I use the phone's camera. 
Of course I forgot the impedance is 200 Ohms not 50 Ohms. So the first test showed up the mistake. After making two resistor matching sections I got the desired result.
It should look a lot better but the loss of the matching sections modifies the overall loss. However it shows at least 40dB suppression for the second and third harmonics. It will do the job.
The 'test' construction i…

What was I thinking?

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First of all, I needed to design a low-pass filter for the Raspberry Pi. To 'clean up' the output. It is a square wave after all, with only odd harmonics. A simple task for a Cauer [elliptic] filter.
So I sat down and opened my filter book. Decided on a design I had used many times before. This one 'notches' out harmonics providing very good suppression.
Having developed a spreadsheet to calculate the values, I took a careful look at the components. You generally have two choices, one uses capacitors the other uses coils. The lowest cost version is where you make the coils from scavenged wire. The capacitors can be recovered from old radio equipment. And no they don't have to be Silver-Mica types. Ceramic will be fine.
[I will make the spreadsheet available at a later stage. This will allow the constructor to design the cut-off frequency and impedance to his requirement. Not mine.]
Then it hit me!
It is possible to use ferrites for the coils. But they are neither 'c…

What I wanted to do with some pictures...

Having discovered that the GoPro "free" software only works on 64bit PC's with more than 4GB of memory. It also doesn't have a Linux version... I went looking into the Open Source software. Turns out academia has the solution. So you can process the GoPro pictures under Linux as well as communicate with the camera as well. Just as well. The GoPro is a Linux appliance!
I learnt about making an 'animated GIF' in GIMP. That was fun. But the resultant pictures were only 256 colours and played back on FireFox with shading levels. So I tried making an animated PNG file. That had the quality but was in danger of taking over the hard disk. Certainly wasn't small enough to email anyone.
I discovered a built-in utility inside ImageMagick. Which is there in Lubuntu [Ubuntu]. The utility was "convert" and "mogrify". Both will convert single graphic files to another type. Multiple files will need the mogrify utility.
I then wanted to convert 100+ file…

The plumber has left the building!

So the plumber has gone away with a smile on his face. Sten came and in-between other jobs, fixed my leaky pipe. The pipe had been leaking in the wall for some time...maybe years?
Well the wall and plaster and floor are now drying out.
Me, I am just thawing out. The temperature has climbed to 18C in my study. I wanted to do several things today, but events and people have diverted me again!
So before I forget, let me type this in...

USB bootable stick creation in Windwoes
Insert a USB flash drive into your computer:-

Start a Command Prompt as an administrator (right-click on the entry and select Run as administrator) and type 'diskpart' and then press ENTER.

Next, type the following lines a line at a time, pressing ENTER at the end of each line after the command has completed:

DISKPART> list disk
DISKPART> select disk X
[Note: X is the number for your USB flash drive you obtained from the list command from the previous step. ]
DISKPART> clean
DISKPART> create partition pri…

Amateur Radio in the 21st Century [1]

As I write this, we are still without power after an hour. What made me write this? Well I thought of this subject this morning. All day it has been at the back of my mind. Something for the younger and newcomers to the hobby of “Amateur Radio”.
In the old days, that is before 2000, we amateurs “hacked” our hardware. Whenever someone threw away some thing that we could use, we 'acquired' it. Adapting wartime radios, assembling kits or developing new hardware, we 'hacked' it.
Last century as a constructor you could drive into Johannesburg and visit a component store. Here on the West Rand, you could drive to the top of CR Swart and visit “Vidi-Kits”. These stores have mostly disappeared or service our small electronics companies. Our market here in SA is minute in comparison to a major city in Europe or USA. It is not big enough to support the small number of constructors or electronic enthusiasts. All the components are imported. Attracting import duty. With the exchange…

Amateur Radio in the 21st Century.

Hi All
I have decided to write articles about the hobby. Based in South Africa and relevant to "hackers" of the veteran sort and newcomers to the hobby.
It has become obvious over the last 30 years that the hobby has a shrinking number of "young blood". That is not an ageist term and does not refer to the youth of today. But the "newbies" to the hobby.
The 'hobby' has grown in appeal to certain interested people. Especially with experimentation and communication. No longer confined to H.F. or slow speed analogue modulation. Our hobby has grown in various parts of the world and shrunk in others.
My personal activity has always been hardware 'hacking'. With writing software coming a close second. With the local electronic market at the end of an expensive exchange rate pipeline, it has become almost impossible for low income enthusiasts to build anything. I hope to change that.
With this in mind, let me know what you think.
73 John Brock ZS6WL


Raspberry Pi - session n

First of all, when did you last see an organ grinder?

Today's Q and A session revealed a few things. Dave made copious notes before setting off early for the theatre. But for those who couldn't make it I made a few as well...

Software Mentions

GnuPlot.
I mentioned it and then couldn't get to the examples on the internet. The club house is a victim of a 'slow internet' connection.

GNU Plot home page
Gnuplot Primer
Plotting sensor data using GnuPlot
interfacing early 90’s HQ digital oscilloscope from LINUX
FIR Filters by Windowing - using gnuplot

GIMP.
GIMP - Graphics Manipulation Package
4 Themes That Will Make GIMP 2.8 Look and Work Like Photoshop

LinPSK.
LinPsk - PSK31 for Linux  [download from Sourceforge]
A Slice of Raspberry Pi

WSPR on the Pi.
/WsprryPiforked from threeme3/WsprryPi Raspberry Pi QRP TX Shield for WSPR on 20 Meters

Also mentioned

KICAD - KiCad EDA
A Cross Platform and Open Source Electronics Design Automation Suite.
Thanks Nic!


Audacity - Audacity® is free, …

'Issues' in ugrading Lubuntu

When I made my main PC a dual boot Windwoes XP and Lubuntu, little did I realise that my hard disk was going to run out of inodes...
On researching this 'issue' [we don't call them problems any more], I found that lubuntu or ubuntu keeps updating the kernel. Whilst not removing the old ones. Auto remove [in apt-get] does not flush the old ones. So gradually I had used up all my inodes. This became apparent when I tried to install some new software. It also ran out of disk space.
So when I had a message telling me I had an 'issue' with an update/upgrade with disk space, I checked using 'df'. Nope someone wasn't telling the whole truth. Df said I had a few Gigabytes to play with. So what was wrong?
[Use df -i to show inodes] More research said that I should remove the old kernels, thus freeing up the inodes. Well I did and we went back to the happy situation. For a while. Maybe two months...
Some months ago I had removed [with extreme prejudice] Windwoes XP.…