Thunderstorm in the English Channel

Thunderstorm between Cherbourg and Le Harve

The Meteor M-N2 weather satellite, previously described here, picture received on 20/09/2014 shows a large thunderstorm in the English Channel, completely filling the area of sea between Cherbourg and Le Harve.

Just after I received the picture I grabbed a screen shot from www.lightningmaps.org of the real time lightning strikes from the storm, see below.

The full Meteor M-N2 image I received is below.

Receiving Meteor M-N2 weather satellite

Segment of the first Meteor M-N2 image successfully received

The Russians recently (2014) launched the second in the line of Meteor M weather satellites. Meteor M-N2 transmits Low Rate Picture Transmission (LRPT) format pictures round the clock on 137.100Mhz. This format is of higher resolution that the older APT format.

There have been two excellent people helping with software and advice on how to receive images from this satellite. These are Raydel Abreu Espinet, CM2ESP, and Oleg Bekrenev.

Oleg has provided a program to process the captured signal and produce images like the one you see above. Raydel has provided a GNUradio program to capture the signal.

I don't intend to go into detail about what each program does or why as I don't have time but purely to describe how I received the images and offer pointers to Oleg's website where more information is available. The confusing aspect of receiving these images is that there is more than one way of doing it.

So, firstly my equipment:

• Antenna - homebrew QFH antenna
• Pre-amp - old Microwave Modules 144Mhz preamp
• Receiver - RTL-SDR dongle
• Computer running Ubuntu 14.04, xfce windows manager

The strength of the signal from the satellite is not strong and I did not receive a good signal until I added the pre-amp. The RTL dongle has the necessary bandwidth, it may be possible to use an original Funcube Dongle Pro but this only has 92khz of bandwith and this may be too narrow. I am sure a Funcube Dongle Pro+ will work very well. Not only does this have 192khz of bandwidth but the FCD's are both very much more sensitive than the RTL dongles. Other SDR receivers will also work of course.

So, first thing to do is optimise your receiving set-up and adjust the gain of your SDR device using a known signal source. I use London Heathrow ATIS as this transmits all the time. You need to find the sweet spot of your dongle between LNA gain and IF gain, to maximise gain without overloading the SDR. This is crucial, I copied an 88 degree overhead pass on Sunday and only received a short amount of picture. The next day the image you see here was at about 66 degrees elevation and I got very good results. I have a feeling that finding the sweet spot of the gain controls might be difficult.

Once you have optimised your settings use a program like GPredict or your favourite satellite tracking program to identify suitable Meteor M-N2 passes.

Use Raydel's GNUradio soft symbol decoder to capture the data stream from the satellite and decode to a format that Oleg's image processing program can understand. Raydel's instructions (and a link to the GNUradio program are here, note that this document covers several different method of receiving and decoding the signal). 

The received constellation should look like this is you are receiving the signal correctly.

Once the soft symbol.s file has been received then it is time to open Oleg's LRPTOffLineDecoder program to produce the image. This is a Windows program but runs well under Wine in Linux.

The image above is a part of the window of Oleg's program. If you have captured the signal using the GNUradio program then the processing of the data follows these steps (I think it is different if you have captured the signal in a different way):

• Click the "72k" button (as the satellite seems to be sending data at a symbol rate of 72k but it has also sent at 80k recently).
• Navigate to the place on your hard drive where the .s output file from the GNUradio program is stored, select the file and click ok.
• You should see the two progress bars start to move and the constellation of the received signal show in the top left hand side of the window.
• This step can take some time. 
• If the image can be decoded the infrared/visible channels received will be shown to the right hand side.
• Click "RGB" to generate a false colour image, you need to select the RGB drop down lists to correspond to the wavelengths that were received otherwise you will just get an all white image. You can also change the RGB settings to change the colouration of the image. At this point you can also save the image.

Oleg's website has other examples of images received plus links to the software etc.

The picture below is the full image I received on 16/9/14. The white bar occurs every 6.5 minutes and is a programming error of the satellite code that apparently cannot be resolved. 

This is not a soup to nuts description of how to receive these images. You will need to read the instructions produced by Raydel in particular but it should enable you to capture these images quicker than the several weeks that is has taken me to learn how to do it.

FreeDV - open source digital voice

I had been sceptical of digital voice modes as the standards supported by the major manufactures are all proprietary. This will lead to competing 'standards' along the lines of Betamax vs VHS where early adopters are the losers.

Recently I became aware of an open source standard which will work on existing pc's called FreeDV. I have also realised that digital voice on HF is no different to RTTY, PSK or JT65 for communicating because those modes are also only able to be decoded by computer. Given the woeful state of my CW I may as well add that to the list as well! 

My computer runs Ubuntu 14.04 with the xfce windows manager. There is a FreeDv package available from the FreeDV link above which works with this configuration. I did try to install it on Linux Mint 16 but had problems.

The trickiest part of configuring FreeDV is setting up the sound cards. Two are needed. One can be the standard sound card built into the computer and the other can be the sound card that is built into a USB headset (headphones and microphone).

To configure the 4 inputs and outputs I needed to use alsamixer and pavucontrol (both available from the Ubuntu Software Centre).

alsamixer setup for the internal sound card used for the audio input from radio to computer (using the computer line in socket) (1) Note that 'Input source' is set to the input you are using to get audio from the radio and 'Capture' is used to set the level for that input source.

 alsamixer setup for the Logitech headset headphones (2)

alsamixer setup for the Logitech headset microphone (3)

alsamixer setup for the internal sound card used for the audio output from computer to radio (to be honest I don't know which setting is used here but the socket on the computer is audio out) (4)

 

This is the FreeDV audio configuration screen corresponding to screenshots 1 & 2 above

This is the FreeDV audio configuration screen corresponding to screenshots 3 & 4 above

I also had to use pavucontrol (PulseAudio) to adjust the transmitted audio so it isn't over driving the radio, although I haven't experimented enough to see if I could also do this using alsamixer. I think I should be able to.

I have a Yaesu FT-920 and the audio in/out from the computer is connected to the data port along with the USB-serial CAT cable for PTT control.

What the FreeDV waterfall looks like without a digital signal being received.

That's it for now, there are more instructions for setting up and using FreeDV here.

If you would like to set up a sked please let me know, my email is on the top right of this blog or on QRZ.com (G0FCU).

Arduino Antenna Analyser

Inverted-L SWR plot

The alternative title for this post could be "Even more fun with antennas"! 

I know that the inverted-L that I erected recently resonates on the bands that I wanted it too (i.e. 10/14/18Mhz) but tuning wire antennas to resonance always involves a lot of running between ends of the antenna and rig, taking notes of SWR achieved at specific frequencies and working out whether to shorten or lengthen the wire. 

An antenna analyser can help reduce some of this effort as you get a graph of SWR plotted against frequency. However, these cost upwards of £200. Now bring to the table the ubiquitous Arduino, my favourite 'toy' tool of the moment.

I found several designs for antenna analysers based on Arduino's but I think it was someone on Twitter who pointed me to the design by K6BEZ. If you have an Arduino and a few resistors this is really cheap to make. I had to buy the diodes and the op-amp, but these cost me less than £10 on e-bay with an op-amp and about 10 diodes to spare.

Fortunately I also found Matt Gumbley's website and Matt has designed a Veroboard layout for the K6BEZ circuit. This made building the circuit very simple and it worked first time for me. I didn't have any 50 ohm or 648 ohm resistors so I used a 27R and 22R in series (49R) in place of the 50R resistors and a 470R & 180R in series (650R) in place of the 648R resistors.

Setting the frequency range to scan involves entering the commands below via the Arduino serial monitor. The key commands in the Arduino sketch are:

• frequencyA - set the frequency to start the scan from, in Hz.
• frequencyB - set the frequency to end the scan at, in Hz.
• stepsN - set the number of steps for the scan
• ? - displays the parameters that have been set
• S or s - start the scan

e.g. 12000000A sets the start frequency to 12Mhz.

For a 1Mhz to 30Mhz scan I use 2000 steps.

The results are returned to the serial monitor and in the default sketch are:

• frequency,0,swr,forward voltage, reverse voltage

To get the graphs shown here I have simply copied the data into a spreadsheet, converted the frequency to MHz by dividing by 1000000, and divided the SWR by 1000. I have then used gnuplot to create the graphs.

The gnuplot commands I used are:

set term canvas size 600,400

set output "g5rv.html"

set linetype 1 lw 1 lc rgb "blue" pointtype 0

set xlabel 'Frequency (MHz)'

set ylabel 'SWR'

set xtics scale 2,1

set mxtics 5

plot 'data' smooth bezier title 'G5RV antenna'

Line 2 sets the output filename  to 'g5rv.html'.
Line 8 loads the data from a file called 'data' (frequency and swr, one pair of data values per line, separated by a space) and give the output the title 'G5RV antenna'.

G5RV SWR plot

5 MHz dipole SWR plot

What this shows me is that my G5RV resonates slightly higher in frequency than the 80m & 40m amateur bands but that my 5 MHz dipole and the Inverted-L resonate exactly where I want them to.

Even better is that I have got an antenna analyser for less than the price of a pint of beer. Cheers!

WSPR comparison between Inverted-L and G5RV

WSPR spots using 5W on 20m with my Inverted-L

I managed to get wsprx working in receive mode on my new installation of Linux Mint 16. The realtime waterfall makes it much easier to ensure that your radio is accurately set to receive in the wspr sub-band. I found that my FT920 reads about 40Hz low as a result. However, it crashes when coming out of transmit mode. Consequently, I installed the older version wspr 2.0. This also had a problem with one of the Python libraries but there was a fix documented on the wsprnet.org website.

The waterfall used in wsprx

This means that I can now run wspr with a little more power than previously, my broadband HF amplifier only produces about 0.5W. I have been wspr'ing with 5W and the results using my new inverted-L you can see in the screenshot at the top of the page. I am amazed at how far 5W will reach. However, it is a little too easy, on my first transmission my signal was received by KK7UQ on the west coast of the USA.

After an hour wspr'ing on the inverted-L I switched to my G5RV and the difference is considerable. Although the G5RV is higher than the inverted-L (around 12m versus 6m high) one leg runs E-W and the other leg NW-SE. The inverted-L runs SE-NW pointing directly at north America. The resulting wspr spots from the G5RV are below.

WSPR spots using 5W on 20m with my G5RV

Interestingly I received VK3HAD equally well on both antennas and KK7UQ received me equally well until dusk fell when a few more US stations heard me and were heard by me. 

Along the greyline I was heard by ZL3DMH at 19016km distance.

This isn't a scientific test, by any stretch of the imagination but very interesting none the less. However, what it has shown me is that 5W and wire antennas equals QRO in wspr terms!

Inverted L and results from WSPR

Good results with my new Inverted-L overnight. Running 500mW I got multiple decodes from the stations you can see on the map above.

The tx is the same homebrew amplifier that I have used previously so the antenna is the only item I have changed. With my other antenna, a G5RV, I had only been received once in the USA.

Overall this confirms my initial findings that the Inverted-L pointing at north America is performing very well.

4 metres contest

Screenshot of my QSO's in the 70Mhz Cumulative contest on  25 May 2014

Many years ago I participated in many VHF and UHF contests with the G4VAT contest group so I sort of got drawn into this 70Mhz contest today. I have described my new 70Mhz elsewhere on this blog and this was a good opportunity to give it a good try out with my homebuilt Moxon Rectangle antenna.

The result was that I worked all the stations that I heard, except one who was a long 230 miles away. He heard me on an aircraft reflection but it didn't last long enough for a full exchange.

I was pleased to note that most signal reports I received were reciprocal to those that I gave out. There was deep QSB on most signals and comments made by stations who have submitted logs also note the QSB and generally poor conditions.

Here is a link to my contest QSO's in an interactive Google map

I have just submitted my log to the RSGB contest committee site and I have claimed the grand total of 825 points!