A Radiosonde Chase in Two Acts

It started when Mark Jessop sent me a message notifying me that there was a sonde down not far from where I work. The ill-fated RS41 launch RS_N3940146 reached an altitude of only 2083m before descending again. Unlike all the other sondes launched that day that ended up in far eastern Victoria this one came down comparatively close to the launch site.

An opportunity too good to pass up, I decided, after some encouragement from my colleagues, to “go out and get a coffee”. I grabbed my bike and went for a short ride to the landing zone. But a not so infrequent problem occurred…

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Radiosonde Chase Semi Success 2018-03-10

The story starts much like any other chase. The landing location looks good, “only” 45km out of suburbia this time. We grab our stuff, get in the car and watch it ascend from the ground station while driving out to somewhere near the landing zone. We’re eager to catch it, hoping it will be our first recovery of a Melbourne-launched RS41 - up until quite recently they were still launching RS92 sondes.

This was only made a little more interesting by the fact that I was working on the receiver code to allow two concurrent instances to run - under the impression that I could always git stash in the event that I needed it running right now. Turns out that was wrong, as some un-committed local changes had been made - should have checked, but wasn’t on my machine…

That proved to be no problem as I got the feature working by the time the balloon was at about 17km altitude. The code change meant we could simultaneously run the vertical and the cross-dipole on two different rtl-sdr receivers at the same time. Mark Jessop initially suggested switching between them with a coaxial relay - however looking for a suitable candidate revealed that buying a second rtl-sdr was actually the cheaper option.

The descent was still relatively uneventful - aside from the prediction being fairly off as the weather was in the process of changing. The balloon burst and began to freefall - and thanks to the newly implemented feature, I could see exactly how much better the cross-dipole was at picking it up in this phase of flight. But something interesting happened next…

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Kogan Smart Tv Hacking

I recently purchased a Kogan 43” Smart TV (KALED43KU8000SZA), and I’m not entirely happy with it. Since the invention of the instant-on CRT in the 1960s, TVs have been able to switch on in mere seconds. Nearly 60 years on from that, I hit the power button, wait for Android to boot, and 30 seconds later, this:

It’s displaying input from my OSMC Vero 4k - and yes, then I have to use the menu controls to select the input, before it displays fullscreen - every time. It’s a small annoyance, but it’s a significant one - the TV has one job…

I wanted the “smart” features to play with, but it appears I’m being forced to. This just won’t do, so Michael Wheeler and I took a look and we fixed it. Read on to find out how.

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LTE Gateway - the build

“In theory, there is no difference between theory and practice. But, in practice, there is.”overheard at a CS conference by Walter Savitch

In the previous post, we went over the theory of building a LTE gateway.

In the build phase, I obtained a Mikrotik RB2011, a 9AH SLA battery, a PicoUPS, a Sierra Wireless MC7430 in a miniPCIe to USB converter, two RFI XG884 antennas and some patch leads.

And here’s the finished product.

The build process began with getting the router to talk to the modem.

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Ozonesonde RS92 Hunt 2018-01-15

The “normal” radiosondes are launched twice a day from capital city airports at the international standard of 45 minutes before 00Z and 12Z (midnight and noon UTC time).

However, on occasion we’ve received some interesting signals from sondes that appear to have been launched from the general area of a location in Broadmeadows - which a bit of judicious Google Street View stalking reveals to be BoM’s training facility.

These appeared to be a mixture of the old fashioned RS92s and the new, much more desirable RS41s. While RS41s are quite nice, further decoding of the RS92 signal revealed something even more interesting - it had an auxillary payload to measure ozone.

Noticing one launched early Monday afternoon (a surprise because we’d previously only seen launches from that facility on Wednesdays and Fridays), Michael Wheeler and I decided to attempt a retrieval mission. Due to work commitments, we couldn’t just drop everything and run, so we decided to head out after work and hope it was still sitting where it landed.

The signal was received down to about 1500m altitude - an encouragingly good result leaving us with a search radius of about 1km. The plan was to drive out there then drive around until we receive the signal, get GPS coordinates then find it.

We drove two hours out there, we received the signal but then there was one small problem.

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Good News From 10Gbit Land

Previously in 10Gbit Land…

Browsing through Mikrotik’s RouterOS changelog I noticed something.

6.42rc6 includes this (Yes, this was a while ago - I’ve been busy):

*) crs317 - improved transmit performance between 10G and 1G ports;

Is this what I was after? Let’s try it out…

Connecting to host 172.16.1.20, port 5201
Reverse mode, remote host 172.16.1.20 is sending
[  5] local 172.16.1.19 port 55268 connected to 172.16.1.20 port 5201
[ ID] Interval           Transfer     Bitrate
[  5]   0.00-1.00   sec  78.5 MBytes   659 Mbits/sec                  
[  5]   1.00-2.00   sec  75.9 MBytes   636 Mbits/sec                  
[  5]   2.00-3.00   sec  77.8 MBytes   653 Mbits/sec                  
[  5]   3.00-4.00   sec  79.3 MBytes   666 Mbits/sec                  
[  5]   4.00-5.00   sec  77.7 MBytes   652 Mbits/sec                  
[  5]   5.00-6.00   sec  76.9 MBytes   645 Mbits/sec                  
[  5]   6.00-7.00   sec  77.2 MBytes   647 Mbits/sec                  
[  5]   7.00-8.00   sec  75.9 MBytes   637 Mbits/sec                  
[  5]   8.00-9.00   sec  77.0 MBytes   646 Mbits/sec                  
[  5]   9.00-10.00  sec  76.5 MBytes   642 Mbits/sec                  
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval           Transfer     Bitrate         Retr
[  5]   0.00-10.00  sec   774 MBytes   649 Mbits/sec  6065             sender
[  5]   0.00-10.00  sec   773 MBytes   648 Mbits/sec                  receiver

iperf Done.

Still a few (hundred) megabits short, and a rather high retry count, but certainly better than what we were seeing before - so I’m happy to go back to bridging rather than routing.

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LTE Gateway - the theory

I’m building a LTE to WiFi modem for the car. There are many existing devices to do this, including your mobile phone, so why build one?

I’d like something that can receive a better signal than a mobile phone - especially as our newfound hobby of radiosonde hunting takes us further afield even more than before. And most phones these days are no longer fitted with external antenna sockets. I’d also like it to be permanently fitted into the car, so it’s just “there”. Decent WiFi that extends out of the car would be a plus too.

Here are just a few of the commercially available options for doing this that I’ve collected over the years:

On the left we have the Huawei E585, one of the first such devices. On the right, the ZTE MF70. In the middle, from top to bottom, the Huawei E3872, the Netgear Aircard 785S and the Netgear AirCard AC790S. The E585, 785S and AC790S have internal batteries, and all except the E585 have external antenna sockets.

In this post, we’ll look at why I didn’t just use one of these devices (to be fair, the AC790S still gets a bit of use outside the car) and what hardware I’m planning to build my own with.

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Trouble in 10Gbit Land

All was well, and performance seemed good. Until I decided to pull a large file from the server to my laptop. Despite being almost next to the 802.11ac access point, I was struggling to get even 5MB/sec. It appeared that the noise level on the WiFi channel was quite a bit higher than it should have been. Looking around with a SDR found what looked to be a wireless AV sender blanketing a wide chunk of spectrum in noise. Moving channel only increased performance to about 10Mbit/sec so I plugged into wired ethernet and tested with iperf.

Accepted connection from 172.16.1.19, port 55062
[  5] local 172.16.1.20 port 5201 connected to 172.16.1.19 port 55063
[ ID] Interval           Transfer     Bandwidth       Retr  Cwnd
[  5]   0.00-1.00   sec  17.1 MBytes   143 Mbits/sec  282   12.7 KBytes
[  5]   1.00-2.00   sec  17.3 MBytes   145 Mbits/sec  266   22.6 KBytes
[  5]   2.00-3.00   sec  17.5 MBytes   147 Mbits/sec  264   14.1 KBytes
[  5]   3.00-4.00   sec  17.2 MBytes   144 Mbits/sec  282   14.1 KBytes
[  5]   4.00-5.00   sec  17.3 MBytes   145 Mbits/sec  251   12.7 KBytes
[  5]   5.00-6.00   sec  17.4 MBytes   146 Mbits/sec  250   12.7 KBytes
[  5]   6.00-7.00   sec  17.8 MBytes   149 Mbits/sec  282   15.6 KBytes
[  5]   7.00-8.00   sec  17.2 MBytes   144 Mbits/sec  295   12.7 KBytes
[  5]   8.00-9.00   sec  17.3 MBytes   145 Mbits/sec  268   12.7 KBytes
[  5]   9.00-10.00  sec  17.8 MBytes   149 Mbits/sec  292   22.6 KBytes
[  5]  10.00-10.01  sec   255 KBytes   247 Mbits/sec    4   14.1 KBytes
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval           Transfer     Bandwidth       Retr
[  5]   0.00-10.01  sec   174 MBytes   146 Mbits/sec  2736             sender
[  5]   0.00-10.01  sec  0.00 Bytes  0.00 bits/sec                  receiver

Yeah, that’s not good. Further testing revealed it only affected traffic being switched from a 10Gbit to 1Gbit port.

Tried putting the “stable” and “latest beta” RouterOS on the CRS317, no change. Tried SwOS too in latest and older varieties - although I couldn’t get 2.3 to boot at all (known bug that crashes it on boot if you have any SFPs plugged in (!) but it seems worse than that for me).

I opened a thread on the Mikrotik forums, apparently it’s a “known problem”. I see that the patch notes mention a similar issue on the CRS326…

I’ve changed the network layout to route between two separate subnets, one for 10Gbit and one for 1Gbit. Performance is actually better - in the same configuration, about 950mbit throughput.

Hoping this is fixed soon, because until then I can’t really recommend the CRS317 on a “mixed” network.

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Office Chair Hacking

So I’ve got an outdoor workbench that has a surplus-to-requirements office chair sitting in front of it. The only problem is that the workbench is at standing height, so the chair’s just not high enough.

I originally thought I’d have to get a whole new chair… but it actually turns out that most gas-lift struts for office chairs come in standard sizing - something which actually surprised me as a software developer.

A bit of measurement with calipers showed that the bottom of the strut measured 43mm, and that the top was 28mm. A quick search of eBay then revealed this one with very similar looking measurements. I ordered the HC200 model, and it arrived a few days later, somewhat amusingly with the top section sticking out the side of the package (something had pressed the button in shipping and the strut expanded).

Unlike the kind of hardware I usually deal with, the disassembly process can be summed up as “hit it with a hammer until it comes loose”. If this proves especially difficult, a larger hammer may help.

Reassembly, as they say, is the reverse of removal - reassemble, then sit on the chair to push both ends into place.

(you may wish to place the chair upright before use…)

(also, you may wish to purchase a foam mat in a better colour…)

With the taller strut, I probably wouldn’t lean back on the chair all the way - but it’s now the right height to sit at the workbench for extended soldering sessions, and I didn’t have to buy a whole new chair.

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More News From 10Gbit Land

Well, I bought the CRS317. Purchased from EuroDK for US$315 - best price I could find. Here’s a picture of it:

Brand new piece of hardware and I’ve opened it up already? Typical…

There was one tiny problem - something was rattling round inside. The light pipe for port #2 had come loose in transit.

Not hard to put it back in, but let’s see how it goes on our network…

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