LoRa LoRa Laughs!

Due to the restrictions on airborne amateur radio operation in the UK High Altitude Balloon (HAB) enthusiasts have been forced to utilise licence exempt low power devices in novel ways to make radio trackers for their payloads. I have written plenty on this blog about my HAB tracking, the UKHAS distributed listener network and my own flights.

Until recently the preferred method was to use RTTY transmissions, however the advent of the IoT (Internet Of Things) has seen manufacturers of radio modules develop devices to increase both the range and reliability of communication between ‘connected’ embedded devices.

One such development are LoRa devices, primarily for devices to connect to a global wide-area network LoRaWAN, more information can be found at the LoRa Alliance in addition there are some open hobbyist networks such as The Things Network using these devices.

Using chirp spread-spectrum modulation these LoRa devices are marketed as being capable of robust, interference and fade resistant communication over longer distances and higher data rates.

The UK HAB community has begun experimenting with these devices and one of their keen proponents is Dave Akerman (M0RPI). Dave has developed both payload software for the “Pi In The Sky” PITS tracker along with Anthony Stirk (M0UPU) and gateway software in collaboration with Robert Harrison M0RJX. The ‘gateway’ is the necessary receiver element to upload the data to the tracking system. (all software is on the PITS Github page)

Dave gave an informative presentation on LoRa at the UKHAS 2016 Conference which is now available online (starts around 3 minutes in)


I had intended to fly a LoRa transmitter on my 2015 Hamfest balloon but it stopped working at the eleventh hour and hadn’t done anything else with LoRa till recently.

Spurred on by the conference presentation and the fact more and more flights are carrying LoRa I invested in one of the Raspberry Pi expansion boards sold by Uputronics and built up another prototype tracker with a working LoRa module.

I have done talks at various radio clubs and societies and demonstrated it working but hadn’t actually received a ‘real flight’ as opportunities have been scarce due to the weather. However in the few weeks I have tracked a couple of flights receiving both telemetry and image data, getting a couple of complete images from the imaginatively named ‘SPACE’ flight.

Dave Akerman also flew a flight experimenting with multiple payloads using Time-division multiplexing (TDM). It had 10 small of “AVRLoRaNut” trackers (of Anthony M0UPU’s design) all set to the same frequency (434.450MHz) and same transmission mode. The trackers took turns to transmit, with each one allocated a particular transmission slot in a 20-second cycle. The cycle was GPS-timed but, if any tracker lost GPS lock then it derived timing from the transmissions from the other trackers (the LoRa devices are also receivers) All 10 trackers were suspended from the same balloon. This was in preparation for the ‘Operation Outward‘ re-enactment next year (Steve Randall gave a presentation on it in the above conference video starts 1 hour 16 mins in)

I successfully received telemetry despite the flight not being local and constantly heading away from me as can be seen in the screen shots.

Always a busy man Dave also flew a flight with an experimental camera setup. The SSDV images this time came from a Nikon compact camera, connected to the Raspberry Pi via USB, and using gphoto2 software to take and transfer images to the Pi where they were stored, resized and converted to SSDV format for transmission. These were large images with a high quality SSDV setting so lots of packets per image, approx 1400 per image in testing. 

This flight was using a 868MHz LoRa device, rather than the usual 434MHz due to the IR2030 restriction on bandwidth and duty cycle. Dave was using his Turbo-X or Mode 4 setting which is as fast as LoRa will go within IR2030 bandwidth restrictions (approx 8 packets / 2k bytes per second)

I hastily ordered a 868MHz device and soldered it in the spare slot on my gateway and built a collinear for 868MHz similar to the one I built for ADB-S reception (see video here).

You can see it lashed up just below the dual-band collinear – not ideal mounting and it wasn’t tested in anyway, built blind!  The less than optimal setup at UHF, the insane data rate and the distance (>100miles) were going to make reception difficult, so I was pleased I did manage to receive telemetry and image packets.

 
Most of the current LoRa development in the HAB community has tended to be on the Raspberry Pi due to the use with SSDV and the easy availability of cameras and ready built kit. LoRa is of course available on the Arduino platform and I had purchased a couple of ‘Dragino’ shields (pictured below) with a LoRa device on.

Dave has done some work on a AVR tracker software and a simple Arduino ‘Serial’ LoRa receiver. The receiver connects to a host PC appearing as a serial port and by running some gateway software the receiver can be configured via the serial link and received data is sent back to the gateway to be uploaded to the Habitat tracking system and SSDV system – the software can be seen here during the ‘Operation Outward’ test flight.

This gateway software is written in Pascal using Delphi and is not as functional as the Raspberry Pi Gateway software. Dave has made the source code available but I am not au fait at all with Delphi however I installed the free development IDE and intended to get in and make modifications but it seems to require a non-free(?) library for the serial comms so ditched the idea.

Instead I have spent the last few days developing a C# .NET version using Microsoft Visual Studio (the community version is free) and also have been modifying the Arduino code in the receiver to add functionality, such as storing the SSDV images locally.

It is still a work in progress but I have made a video showing the current state


Anyway as Cilla Black would say it’s been a Lorra Lorra Laughs!

Having fun on the “Magic Band”

In April I installed a second-hand HB9CV for 6m, primarily for use in the UKAC VHF contests but I hoped to use it during the upcoming sporadic ‘E’ season.

Still a relative newcomer to the hobby (only licensed at end of 2013) I had little experience of the 50MHz/6m band and have been mostly met with static whenever I did turn the dial to have a listen but happily that has changed in the last few weeks.

I knew that 6m can be an interesting, unpredictable almost unique band.  Being at the lower end of the VHF spectrum it exhibits the usual characteristics of VHF communication, mostly short range line-of-sight contacts since 50MHz is usually well beyond the maximum usable frequency (MUF) for normal ‘F-layer’ ionospheric propagation utilised by the lower bands. However solar activity and other factors can trigger other types of propagation, in fact the band can support just about every form of propagation possible and is the main reason why it has become known as the “Magic Band”

One interesting form of propagation is sporadic E, or popularly referred to as Es. Small clouds of unusually ionised atmospheric gas form in the lower E-layer of the ionosphere (located at altitudes of  90 to 160 km). These clouds ‘bounce’ the radio waves allowing long-distance communication at VHF frequencies, sometimes multiple hops are possible giving extreme DX. One advantage of sporadic E over other forms of propagation is that it allows low-power QRP communication. As its name suggests, sporadic E is not a normal occurrence but can happen at almost any time. It does display a seasonal pattern with activity peaking in the summertime most noticeable in mid-to-late June.

I had turned the antenna to the East and have been running WSPR on and off over the last month on 6m with no luck, just the odd spot from the UK. I was in the shack one Saturday evening and was tuning around on 6m and heard some Italian stations calling CQ on SSB. I tried my luck and answered (using 50W) and was amazed to be heard, working a couple of stations in quick succession then suddenly the opening closed mid contact with another station. I was hooked!

Over the past few weeks I have caught a few more openings and have managed to work (in no particular order) Latvia, Croatia, Lithuania, Slovenia, Czech Republic, Slovakia, Serbia, Italy, Germany, Switzerland, Poland, France, Spain, Austria, Canary Islands and Finland – using a combination of voice on SSB and the JT65 digital mode.

Using JT65 has been particularly interesting since it allows me to ‘remote operate’ from work otherwise I would miss most of the ‘Es’. Being able to monitor the waterfall and see the signals gaining and falling in strength during the minute long transmission is particularly fascinating.

Using the PSKReporter website I can see the location of all the stations I could hear and was being heard by. This map shows activity over the couple of hours on the 26 May using just JT65.

I have joined the UK Six Meter Group (UKSMG) to find out more about this “magic band” and their website is full of lots of information and resources along with the magazine Six News for subscribers.

Inverted L

I have been lacking the ability to operate on the lower HF bands, while my small ‘multi-band’ OCFD could be used on 40m trying to use it on 80m was nigh on impossible with my ATU. As you would expect even if matched for a useable VSWR the actual performance has been compromised.

I needed a cheap and relatively unobtrusive solution and I found one in Len Paget’s (GM0ONX) design for an inverted L. The full details were printed in the Practical Wireless magazine several years ago and PDFs are available for download from Len’s website. The designs make use of coaxial traps, one for the 80m version, two if you want to add a top-band (160m) option.

Opting for the smaller 80m version I set about building one. Using an old fibre-glass fishing pole about 5m high at the far end of the garden tucked behind the summer house which I could collapse down and then retract the wire elements when not in use so hiding it from view.

The fun and interesting part was building the trap. They are formed by coiling some coax, in this case RG58, round a former such as plastic waste pipe. I had a bit of scrap pipe but it was 32mm not the 40mm diameter type described in the article, thinking it couldn’t make ‘that much difference’ I built one using the same number of turns but the resultant antenna wasn’t anywhere near resonant according to the analyser.

I decided I needed to test the trap’s frequency response. I found a YouTube video by Dave Tadlock (KG0ZZ) where he demonstrates using a MFJ ‘Grid Dip Meter’ adapter on an MFJ antenna analyser to test coaxial traps.

The adapter consists of nothing more than a coil of wire on a suitable former so I made my own to use with my AW07A analyser. It worked a treat and I discovered my trap was way off frequency. In the mean time I had located a useful PDF document by David Reynolds (G3ZPF) which informed me I actually needed 180cm of RG58 round a 32mm pipe to make a suitable 7MHz trap, so I made another.

I made a small video showing the traps and how I tested them.

The resulting antenna seems to perform well, but it does sag a little due to the weight of the trap and wire and the flimsiness of the pole. But I have made a number of contacts on it and used it during the RSGB 80m CC Datamode contest a few weeks back. It was my first go at this contest but once I got the hang of operating it was great fun.

6m/70cm antenna updates at the QTH

I have made some changes to my antenna set up. A local amateur was selling a second 13-element 70cm yagi and a 6m HB9CV antenna at a low price so decided to acquire them.

The 70cm yagi was to replace the small 7-element one which I pressed into service as a hand held antenna for potentially finding my HAB payloads last year.

To be honest I wasn’t really after a 6m antenna due to the size and visual impact. I have a 6m ‘wooden’ moxon I made back in 2014 but it is heavy, ugly and unstable so had been collecting cobwebs in the garage. I decided with the prospect of ‘Sporadic E’ season around the corner I would be foolish not to put it up.

The HB9CV wasn’t in the best of conditions but seemed complete albeit it was purchased dismantled. The elements were a little weathered so I set about cleaning them up with a light rubbing down with some wire wool and a rag with a drop of WD40. On closer inspection the tube that made up the front element had some noticeable bending and on removing the plastic mounting to investigate I spotted a crack in the tube wall by the hole for the mounting bolt.

While it hadn’t totally separated it would only be a matter of time before it did fail as it was flexing, the plastic mount was the only thing holding it together. I found a suitable piece of alloy tube from a scrap antenna which was a perfect fit inside the broken element. I cut a suitable length and pushed it up inside the element to the appropriate position and then simply drilled through and bolted either side of the central hole to stabilise and strengthen it (can be seen in image below)

The next issue I had to address was the feed point, it came with about six inches of RG58 coax projecting from it where it had simply been cut for removal by the previous owner. I prised off the cover cap to find it full of water, the reason being a hole in the back and it being stored outside I believe.

Thankfully the trimming capacitor seemed okay, while it was wet it wasn’t corroded. It was all dried out and the hole plugged with silicon and I set about re-assembling the antenna which was a little fiddly to get the phasing line to sit properly but once done it was a simple matter of adjusting the capacitor to get the VSWR to a minimum in the SSB section of the 6m band. I mounted on the rotator pole just below the X50 collinear.

I used it last month in the 6m UKAC and while my operating not exactly earth shattering I was happy with its performance using just 10W in the low power section just “search and pouncing” for a little over an hour.
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The 70cm Yagi was straight forward as was already assembled, I just had to make a slight tweak to the gamma-matching bar as the VSWR was unexpectedly high around 2:1 in the SSB segment of the band, it seemed to have been tuned for the FM portion of the band. I managed just an hour “search and pouncing” in Aprils 70cm UKAC, I started late and while signal reports both ways were a marked improvement I found the extra directionality and off beam rejection something I will have to get used not helped by a temperamental rotator. 

Some Radio Antics

Shack activity has been curtailed with the antenna ‘mast’ spending a lot of time luffed over due of the winter storms and high winds that have battered the UK over recent weeks.

Thankfully things calmed down and was able to put the antenna back up but I seemed a little deaf on VHF/UHF dropping several S-points on local repeaters and then started to see high VSWR readings. The incessant rain had somehow got into the connector under the collinear despite being generously wrapped in self amalgamating tape. I replaced the connector and removed a couple of feet of coax in case any had seeped into the cable.

Like much of the UK amateur community I have been trying to listen in to British Astronaut Major Tim Peake during a number of ARISS UK school contacts during the Principia mission on the International Space Station. It is pleasing to see the enthusiasm, interest and publicity it has generated for the hobby.

There is another contact tomorrow (Friday 26th February 2016 at 1440UTC) with the City of Norwich School. While reception of the first two contacts proved a little disappointing for me, the one last week was much better and I made a video during the pass.


The Astronauts are certainly busy on the space station and there was an ARISS contact this morning with an Italian school. It was a low pass here only reaching 7 degrees above the horizon but was pleased to capture Tim Kopra conversing. I was using just the X-50 collinear on the FT857-D


The repaired ATU and a new balun on the OCFD has made a big difference to HF. It is much less noisy and I am now able to match the antenna to 80m something I could never do before. While it will be very inefficient on such a short antenna I did run a little over 2W last night on WSPR as a test, and was pleasantly surprised.

I have also been doing some JT65 and for the first time some JT9 inspired by a demonstration at SKARS and I was pleased to make a JT9 QSO with JA5BDZ on 15m using 10W.

A big help to HF has been tracking down the source of my recent QRM, which wasn’t as many suggested my evil PLT devices but in fact the now redundant wireless router. While the WiFi was switched off it was still being used as a network switch and for some reason had suddenly become RF noisy, it wasn’t the switching PSU but the actual unit and would happen a few hours after being switched on. Funny thing it is not the first time I’ve had an access point suddenly emit QRM.

A couple of weeks ago I went out with Stewart (M0SDM) to assist him flying his kite antenna and we operated under the club callsign MX0SKR, for a couple of hours, it was great fun.


Last weekend I also helped my brother David (M6GTD) install a couple of antennas at the family home. He can finally use the radio he brought at the Hamfest back in September, a Diamond X-50 dual band collinear and a home brewed 33ft long OCFD should get him on the air! 

David helped me at the Hamfest with the balloon launch

My apologies if this blog post sounds like a bit like an excited child recanting his holiday “I did this, and then I did this and I also did that” I hope to post something a little more coherent and structured soon!