Nordintown Blog

Rubbish musings, projects and hackerings from Nordin

Space radio #2 - Space TV

Apr 092015

I am not feeling great at all today and so I took a rare sick day from work and oh look, radio.

I needed to avoid spreading the dreaded lurgie and also to recoop from 2-3 nights of horrible sleep. Rather than sitting back and letting Netflix wash over me, I have resolved to finishing my quadrifilar helix (QFH) antenna project in between coughs. A QFH antenna is a 4 part (hence quad) helical receiving antenna design well suited to the capture of APT (Automatic picture transmission) images from orbiting satellites. I want to make something that I can modify for use with both NOAA/ISS APT/SSTV transmissions, which have their downlinks set to 137.500ish and 145.800Mhz respectively.  

John Coppens (ON6JC/LW3HAZ)[2] puts it better than me:

"The QFH is an excellent antenna for satellites, as it receives from 'the entire northen hemisphere', from horizon to horizon, with all the sky in between. Such an antenna cannot have any significant 'gain', as it doesn't have directivity. Such an antenna is not useful for hot spots, as you probably won't have any clients 'in the sky'."

This design [1] looks to be a winner and so I have brought all my parts and tooling together in my study to hammer out something that I can leave connected to an RTL-SDR/Raspi in my loft. I'll take pictures as I go and aim to get it ready for the weekend ISS passes. To achieve this, I need to:

  1. Check the calculations for the two cable loop lengths, spur lengths, height and distance apart using the target wavelength and core thickness [3]
  2. Mark, drill and cut upon my large and small spur pipes using the measurements obtained; and
  3. Solder the wires of correct length to variboard in the correct way.

All doable, so lets go.

Given the wire I am using (1mm wire stripped from a 3 core electrical cable), the calculations turn out to be: (145.800Mhz137.500Mhz)

Large cable loop: 2223 mm / 2357.1 mm (Brown wire)

  • Antenna height (H1) = 672.9 mm 713.4 mm
  • Internal diameter (Di1) = 295 mm312.9 mm
  • Horizontal separator (D1) = 296 mm 313.9 mm
  • Compensated horiz. separation (Dc1) = 290 mm307.9 mm

Small cable loop: 2112.5 mm / 2240 mm  (Blue wire)

  • Antenna height (H2) =  639.5 mm / 678 mm
  • Internal diameter (Di2) = 280.3 mm / 297.3 mm
  • Horizontal separator (D2) =  281.3 mm / 298.3 mm
  • Compensated horiz. separation (Dc2) = 275.3 mm / 292.3 mm

Diag 1 shows where measurements map to on the design.

Diagram 1, Copyright © 2015 John Coppens [3]

The source website also includes a very handy template that is generated from diameters of the larger and small tubes given. [Diag. 2].


Diagram 2, Copyright © 2015 John Coppens [3]

I didn't use this as I am drilling holes for both NOAA and  ISS SSTV frequencies. For now I am wiring for 137.500Mhz (NOAA) since I can test it today. All going well, tomorrow I'll cut lengths for the 145.800Mhz ISS SSTV and swap out the cables, moving the separator rods as needed.

I am using 10mm 25mm PVC piping for the horizontal post and old 12mm fibreglass tent poles for the separator rods.  Let the cutting commence.


Not bad. Not great, but not bad. Next up is the wiring. I used polymorphic thermoplastic to neatly bind the wire to the middle separator rods. The wire can be easily adjusted to make the rounded form required whilst holding firm.


The polarisation does matter here, so with the smaller loop (green) running north-south, the wire is twisting counter-clockwise. Soldering next [diag 3].  


Diagram 3, Copyright © 2015 Akos Czermann [4]

A little clumsy, but eventually sorted.


Having made the basic structure and securely wired it, I need to place it somewhere with a good view of the horizon to test against my store-bought Sky Scanner Rx antenna.

The plan is to hang it in the loft and wire it into a Raspberry PI running RTL-TCP via an RTL-SDR dongle.

Results will follow.





Quadcopter Drone Army - Update #3

Apr 072015

I am keen to complete this project, and so I am just about to purchase the following:

  • 15x N-channel MOSFET Transistor, 4.2 A, 20 V, 3-Pin Micro3 (IRLML2502PBF )
  • 2x Hot Swap Controller Bidirectional i2c level converter (LTC4301LCMS8)
  • 5x CD74AC04M, CMOS Hex Inverter 24mA 1.5 → 5.5 V 14-Pin SOIC
  • 10x HC-49 Crystal 25MHz, ±20ppm, 2-Pin

The FETS are to fix one of the quads that has blown it's cheap versions (a known problem, sadly [1])

The I2C level converter is to convert the wiimote logic level to something I can experiment with on an Ardunio Nano v3.

The Hex inverter is used around the crystal along with caps to stabilise the clock signal for the Pixart camera

The 25Mhz clock provides the clock needed to drive the pixart IR camera's onboard IC.

These are mostly SMD components, so I get to gain more experience over dealing with these guys.  I have used variboard with SMD in the past so theres is that, but I might take the opportunity to make a batch of useful 8pin/14pin/16pin smd breakout boards for the space [2].


Space Radio

Mar 212015

Today I drove my small car in an after-work dash to a quiet low cliffside car park in-between the harbour lighthouses.

There I sat intently listening to radio static blasting from my mac. A freshman radio enthusiast, I was planning to receive magic space images from orbit via my magnetic roof antenna plugged into a cheapo SDR radio receiver. The long, drawn sputnik-sounding 'weep weep' with superimposed donkey-like short 'clip clop' of the NOAA Automatic Picture Transmission (APT) signal was my paydirt. After its capture, the audio signal was going to be processed via a simple toolchain to become a beautiful, fully-formed live weather photo from orbit. This exciting outcome was not a given however, as I had found at my last two attempts. I was pretty sure this run would be a success and not a waste of hours. I had brought sandwiches and a banana just in case.

I'd heard about the magic NOAA weather broadcasts from hackerspace radio folk and it seemed like a fun way to use the RTL-SDR and Sky Scanner Rx antenna combo I'd bought on a whim. A number of weeks ago, space members hosted a radio weekend at Aberdeen Uni where folks erected their roof dipoles and made contacts over HF. Making use of the roof also, I played with receiving the NOAA signals, sprinting to the chilly roof when the sats passed overhead. Orbiting National Oceanic and Atmospheric Administration (NOAA) satellites circle pole-to-pole 540 miles above the earth. NOAA have a few sats up there and the three main APT players - NOAA15, NOAA18 and NOAA19 - pass overhead a few times a day. NOAA15 and 18 have their downlinks as 137.6200Mhz and 137.9125Mhz respectively and seem to be the strongest signals for me.

To track sat passover times, I found gpredict [1] to be a great open source tool that can be installed cross-platform. To capture the actual audio via an RTL-SDR once I had a sat overhead, I used GQRX [2] for the mac set to narrow FM, but SDR# does a great job on a windows machine. On the mac, outgoing audio can be directed to an input device via the virtual soundflower device and recorded via Audacity set to a sample rate of 11025hz. On a non-mac, you’ll probably have a ‘stereo-mix’ device in place already. The resulting wav file then needs to be imported into the very cool WxtoImg tool. It does a one-click job of automatically transforming the audio into imagery, even if the signal is incomplete. This was the audio [3] and resulting image [4] of my first attempt. Not great, but a good start. At 38secs the audio is perfect, but it does not last. I sought a clearer, more rural sky, so a few weeks later I drove to the harbour coastal car parks and took a shot there, but the cloudy day seemed to prevent a strong signal. I got the ‘weeps’ but not the‘clops’ :(

So back to the present: there I was in my third attempt, waiting in my little car in a carpark with worlds smallest entry gate (seriously, my Corsa barely fitted past). After waiting a spell, I started to hear shadows of that magic sound. I had run my mac battery down by this point and I did not want it to die at this crucial stage. I plugged in my car charger for more juice. Not long after, I COMPLETELY lost the signal. Having not started the audio capture I was pretty pissed when no tweaking about the freq made any change. The sat was still in full view but I was getting nothing with 3mins till LOS. Infact the entire noise floor had raisen up (that should have been a clue). I checked the usb/coax connectors and roof aerial but no change. The sat passed below the horizon just as I realised that I had started the car engine to make sure my charging laptop and phone would not kill my car battery. Stopping the car brought the noise floor back to normal. DAMIT DAMIT!! Thats how I learnt that using cheap radios from inside a car sometimes work better with the engine and chargers off. Feel free to write that down if you are a radio dumbass like me. On the plus, I guess I forever learnt something new about SDR radio and found a nice radio spot, so not a waste of hours at all.

If *you* want to have the same (or hopefully more successful) raw audio-to-imagery experience, you should hurry. The APT sats are getting pretty old and cannot hold orbit forever. NOAA APT transmissions are scheduled to die from 2017 [5] and will be replaced with something digital. Boo hiss boo. If you do have a go though, for gods sake make sure you bring sandwiches. It seams brains are optional.



31C3 - Workshops

Jan 292015

For me, 31C3 was all about the workshops.  I reasoned that these were the things I could not catch up via youtube and would be the most engaging. It was a good call.

I attended the obligatory lock picking workshop and spent most of the time moaning about the hit-and-miss nature of the art with chatty strangers. I didn't actually unlock anything, but joined in the merriment when the chap next to me did. He admitted he had resorted to mashing it by that point also, and that blind luck was what opened the thing. Whilst I was poor student, the teaching guys really knew their stuff so I brought a small pick set and follow-up guide booklet in gratitude. I'll learn the german language at some point so I can read it.

Next, I has earlier learnt that a fellow 57north hacker had pledged some money to some food hacking group and had cooked up some sweet sounding lamb in their prep area. I tagged along to found a full-on kitchen with shelves of food and tables of people cooking and tasting. 

The kitchen residents, The Food Hacking base (FHB) are a bunch of hackers from all over the world who share the love of experimenting with food and beverages. They have a very inclusive mindset and openly invited anyone interested in the sport to take part - I found myself taking part alot over the event. The idea is that those interested pledge money before hand, but being late to the party I donated at every visit instead. We know time follows skewed tangents at events like 31C3, and concepts like days and schedules collapse. Accordingly, I am a little fuzzy about the order of the happenings:

Whiskey Tasting
Random people brought in bottles from their own locales (Me too, but I left my bottle at the apartment grrr). I learnt that I prefer smokey whiskeys to peaty - awesome to know. Simulates that comforting experience of smelling the Friday-night bonfire on a shitty work Monday, via that scent-impregnated scarf. 

Cheese and beer tasting
Same as with the Whiskey tasting, a wide range of donor beers and cheeses that FHB people arranged into plated groups.  In terms of taste revelations, the nameless Lavender cheese was quite cheeky, with a very soggy german brie'ish blob (sorry no name either) found to be plate-lickingly gut.

Of particular pleasure was the Makgeolli, a rich runny-yogurt-like beer native to Korea, fermented using nuruk, a dry a wide clod of many microbes. I learnt that the resulting microbial orgy creates a great deal of CO2 and when opening the bottle, the entire contents generally ejects out in your face. Double bowls are needed to prevent messy disappointments on bottle opening.   

Sushi hacking
I missed this but honourable mention to the black pudding sushi served with a whiskey chaser. Most creative.

A guy was working on recipes to make insects (meal worms in this case) more palatable by grinding them up into power and using in cookies.  Tasted like cookies to me, so bravo.  I was inspired to take the opposite route with a fresh hunk of pork cut from a large hung leg (used as a sign for the FHB until time came to eat it).  When dipped moist in to dried meal warms, it tasted like a crispy ham nugget but yea, looked like something an Ork would serve at his we-conqured-the-shire dinner party.  

Local and homebrew tasting
Lots home-brew with people explaining their creations around the table.  Ranging from nettle wine, ciders of different ages, prison hooch (served complete with zipbag, straw and bucket) and working-mens beers. I really wish I had taken some notes, as it happened I got progressively jolly and make friends instead. Good call.

The people: the real magic at the FHB 

Those running the space give a HUGE amount of their time to the group and I for one really appreciated their efforts. People can just rock up and help, which I did where I could.  Certianly I encourage anyone in the vicinity of a FHB event to offer their help - you will have a great time! After experiencing the cheese tasting, some of use stayed to prep the next session with the remaining cheeses. After, I found the whiskey I'd forgotten earlier. As others found their stashes,  we had a follow-up evening of fine sampling with bread, meat, cheese and spirits. I think it was here decided I wanted to make some Viking (i.e. wild) mead, and I got a lot of roaring drunken advice about it (which seemed topic appropriate).

Certainly I shall be pledging ahead for CCC camp and if the above sounds fun, I recommend you do also.

31C3 - Settling in

Jan 272015

Our 57north people had been assigned a table in the international hackerspace area, denoted by a stand displaying a world map with odd stickers. Early-on we started inviting visitors to add their stickers since ya'know.. stickers.

On arrival, it was clear that the sign also had an odd amount of plumbing attached to it. I learnt this was an unconnected delivery node to be used as part of the event's vacuum tube delivery system, which spread over the entrance floor areas.  People were using the tubes to send all sorts of awesome crap from node to node. Occasionally near our table, LED lit pods could be seen and heard zipping over the plumbing, typically followed by a harsh crash as the tube contents escaped the catching cradle and ejected to the floor.  This sound signified possible presents - it was a good sound.

The floor area our table was in was one of the darker areas intended to allow hacker-built lighting projects to shine in their glory.  Around us hung a smörgåsbord of lit globes, chaser lights and fire effects. I had brought along an ATtiny-powered 80-led light strip of makeit:glow fame that, while pathetic in scale, still stood proud on our adopted world map board. The light preset was fixed to 'drunk, gay cyclon' which I felt added a particular foamy joy to the ambience. Special mention must be given to the large LED sign that invited all to send text to it via UDP packet. I witnessed deep conversations between a fellow 57north hacker and random others:

Them (paraphrasing): "You cannot spell"
Him: "Patches welcome"

Also, there were talks. I am not going to describe the talks much as they were all recorded and can be viewed on youtube. The following are ones which I would recommend:

I will add to this as I watch more videos. 


31C3 - Arrival

Jan 262015

From Dec 26 to 30th, a bunch of us from 57north hacklab travelled to Hamburg for the 31st Computer Chaos Club Congress, held at the Hamberg Congress Center.  Over the 4 days, the building was transformed into essentially a mecca for hackerspace members, and a holy shrine it was indeed.

I flew from Aberdeen International Airport around noon on Boxing day and arrived at the congress centre around 5pm Hamburg time. The trains connecting me between the airport and the center ran with typical German efficiency and the guide from the CCC wiki was spot on, advising me to avoid a line closure by taking 3 extra connections. I found out later this advice was from last years congress and therefore redundant, still it was refreshing to travel the German version of the London underground - rather reminiscent of playing one of those familiar yet novel reinvented monopoly variants where your electric company has been swapped out with hot sausage vendors.

The evening was bloody cold and upon leaving the station, I delicately asked a waiting couple of apparent natives if they knew where the CCC conference was. Smiling American accents told me to simply look to the big ass building and walk towards it.  The building was indeed big and I saw that in a stroke of genius, the Orga (the name given to those in charge) had hacked the giant CCH sign of the center to show "CCC" with what I presume were LED strips and black bin liners. Couldn't help thinking that this would not be allowed at the UKs NEC.

Entering via the buildings main lobby, I toured the heaving spread of caffeinated hackers. I zigzagged under hanging lighting spectaculars between people hugging laptops and engaged in animate conversations. Imagine 8,000 youngish NASA Engineers had been ripped away from their rocking casual Friday after-party and tasked to save the current manned mars mission, using only the IBM ThinkPad's, RGB lights and 3D printers that the astronauts had laying about. I caught this sense room after room. Framing the action were large vacuum tubing installations dotted either side of a starship-themed central lobby corridor. Occasional dance beats could be heard out-thumping the assorted pockets of vocal babbling as people entered and existed the beautifully hacked-up dance club bolted to the side of the entrance lobby spaces.

Taking all this in with my sluggishly English brain, I recall thinking how could any building official allow such freedom? They must have been either complicit and embedded in the vast t-shirted crowds somewhere, or hidden deep inside their city flats calming their shattered nerves with the best whiskey that bribes can buy.