SSDV equals Laptop Mania

I’ve been recently hunting for a laptop or computer I can run Linux on to allow me to participate in a Slow Scan Digital Video SSDV experiment from a High Altitude Balloon.   Some of our AREG club members are developing a high speed FSK modem that is capable of 100kbits or more on 70cm.  Over this high speed link digital images are sent throughout the high altitude balloon flight, the combination of SSDV and high speed FSK has been named Wenet.  These SSDV images are reconstructed on a server in the UK from multiple ground stations streaming their data (click).   Recent testing has shown that the on-air performance is less than 1dB away from the theoretical maximum, David has written an excellent article on it here (click).  However if I wanted to join the fun I need something to run Linux on.. Hmm what to buy.

So when one of my AREG club members emailed our club mailing list with details of a local computer recycling shop selling refurbished HP Probook 5320m’s for $100.  How could we go wrong.

The Intel i3-370M processor is relatively old and puts this machine at the low end of the performance curve, but with 4GB or RAM and 250GB 7200rpm drives these laptops still offered good performance and excellent bang for buck.

So once I’d visited the computer recycler and purchased a laptop it was installed with Ubuntu 16.04 LTS and the usual upgrades and massaging applied to make it all work.  This was the first time I’d experimented with Debian Jessie but the end result was a working machine.   By working I mean working, so the Wifi, Bluetooth, battery monitor, webcam, touch pad, buttons, keyboard, USB, Display port all just simply worked.  There is something to be said for sticking with non-bleeding edge hardware.

The Wenet installation is relatively painless if you’ve ever compiled things from source.  This was then married with a RTL-SDR and 70cm preamp.   The big test was then Horus Flight 39 in which said laptop and system were put through there paces by my eldest son Daniel, you can follow the write up here (click).   The entire team in the tracking car were amazed to watch the pictures “live” from the balloon on this flight.  I had to concentrate on the road a lot of the time with people making oooh and ahhh sounds around me.

I’m told the processor was loaded about 30% the majority of the time and the machine remain responsive under load.   This will certainly do very nicely for this experiment going forward.  What is also strange is I now find myself sitting on the sofa of a night time using this laptop in anger surfing the web.  It boots fast and is great for “looking things up”, so far it’s run for 5-6 days without needed to be charged.

Now to work out what else we can do with it !

Waverley Amateur Radio Society Powerpole Kit

(c) Waverley Amateur Radio Society

A few members of the AREG got together and purchased a group buy of the Waverley Amateur Radio Society Powerpole Kits to build.

I got mine for my contesting setup since they were cheap and cheerful and I could screw my West Mountain Radio RigRunner under my bench.

Construction of the units is not difficult and the instructions are nice and clear.   A job well done by the WARS that is for certain.

However with power distribution you’re always wondering just how much current can you run through them without damage.

I’m luck enough to have access to the nice toys at work for testing of power supplies.   So I ran up our grunty PSU on the input, connected the load to output 6 (furthest from input) and ran up a conservative 25A continuous as the worst case and waited.   The majority of my “contesting” radios will reach 25A peak with an average far lower than 25A, should be good enough.   It does mean I’m not too worried if two radios were used at the same time however.

Using a thermographic camera I was then able to go looking for what is “getting hot” a sure sign of something under stress.  After 10 minutes of “thrashing” the temperature stabilised and I was able to capture the following two images.

ir_1367ir_1368

The first image showed me that there was something getting hot at this power level (345W) my initial thoughts were the copper traces or a dodgy solder joint.  It turns out it’s the fuse if you look at the second image.

These automotive blade fuses run stonking hot at high current levels, far hotter than I’d ever considered before in the past.   Keep in mind that these are 30A fuses and were 15% within their rating at the time. This stands to reason when you consider that the fusing capability of such an element is a function of the current (I) squared and time (t).  So the higher the current the shorter the fusing time, the squared term ensures that the relationship is not linear.  The heat from the fuse was far greater than the heat from the traces.

Anyway my rough tests and thermographic images certainly tell me that a properly constructed WARS powerpole kit will happily run within it’s designed ratings of 30A continuous on the input.   Time to order one or two more for the junk box me thinks !