LF and MF reception in an urban environment

SW listening and the ability to receive stations many thousands of miles away on HF has always fascinated me. Reception on HF, more especially LF and MF has always been a challenge due to the high urban noise floor.

The doublet antenna at home while working well on 7 to 30 MHz, is a poor performer below 3 MHz. This coupled with the high noise floor makes reception of all but the strongest signals very difficult. In part the answer is a dedicated antenna for low frequency reception. Options range from very large beverage / directions arrays to small active antenna. I have no experience with large antenna on sub 7 MHz, as the average urban garden will not support such ambitions projects. The answer for many of us comes from a surprisingly small antenna.

Receive only active antenna may provide a solution, the active part providing some amplification in the receive path. Designs are available for both commercial and homebrew, the price can vary from a £20 homebrew solution to £250 commercial antenna.

I was lucky enough to spot a second hand Wellbrook loop on ebay, reasonably cheap and this gave me a chance to compare the performance with my other HF antennas. It also provided me with an opportunity to monitor WSPR signals on 472 KHz and provide some data into the WSPR network.

Commercial 

Wellbrook Communication have a number of versions available, comparison of models here.

Cross Country Wireless  with a FAQ

Homebrew

PA0RDT has designed a LF / MF Mini Whip antenna, you can read the fundamentals of the mini whip.

M1GEO has recently repaired a Wellbrook loop antenna, his website includes a detailed teardown.

LZ1AQ has detailed design notes on his website for his wideband active loop antenna.

PA0LUX provides a video demonstrating HF reception on his wire antenna and Wellbrook loop. You can see and hear the difference for yourself.

How well does the Wellbrook work on 472 KHz

Well it outperforms my doublet antenna by some considerable margin. Signals that I cant hear just pop out of the noise and for interest I have included some WSPR data for that band.

Monitoring 472 KHz on the evening of 15th and morning of the 16th Jan 17  provided 19 unique calls.

DC0DX, DH5RAE , DK2DB , DL6RCN , F1AFJ , F6ACU , F6GEX , G3KEV , G3XBM ,G7NKS , LA1BCN LA1TN , LA8AV , M0PPP , ON5TA , PA0A  F5WK, F6HCC , G8HUH.

The best DX was LA1TN at 1346 KM

Its also interesting to look at the reception reports over time of day / night.

 

 

 

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Oak Hills Research QRP RF Power Meter (WM-2 QRP)

The Oak Hills research produce a very nice QRP power meter kit, the RF power meter WM-2 QRP is produced with a high quality case and silkscreened and masked PCB and a large moving coil meter.

Meter Highlights

Operates from 300 KHz to 54 MHz

Measured power range from 100 mW to 10W FSD with an accuracy of 5%

I built one a few years ago, and found it very helpful when measuring QRP power from the FT817 and Ultimate 3 QRP kits.

The kit comes with everything you need, instructions are provided in the pack and takes a few hrs to build. The kits are available online and currently cost $129.95 and can be provided with BNC or SO239 sockets.

You can calibrate the meter without the need for any special test equipment.

Ive included some pictures of the completed meter, and think you will agree it looks very professional. Power is provided by a 9v battery or external supply.

Oakhills QRP meter

Oakhills QRP meter

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Ultimate 3S QRSS/WSPR project

Some month ago I purchased a Ultimate 3S QRP transmitter from QRP Labs. The latest version is the ultimate 3S and it comes with a number of options.

Over the christmas holidays I decided to make the project, inspired by Dave G7UVW and George M1GEO activity on QRSS over the holidays. I have used WSPR before from home, but really wanted a QRP transmitter that I could leave on over night, without running the main radio. The answer is one of these kits, as they are very low power consumption, and flexible enough to run multiple modes / bands.

The transmitter can be configured to run on any band between 2200m to 2m (136 KHz to 144 MHz)  with a suitable low pass filter. I have linked a table showing actual TX frequencies online.

I had purchased the Ultimate 3SSi5351A synthesiser module, Low Pass Filter for 14 MHz and the QLG1 GPS unit. Other kits / options are available, and the project is modular so you can pick and choose the options that work for you.

I found the instructions really easy to follow, and coupled with the pictures component identification was easy. I did use a magnifying glass to check some of the component values, and the “quality” of my solder joints. Starting with the GPS module, and then the synthesiser I found the build easy to complete. I then moved onto the main 3S transmitter, this again has various options, but I decided to get the basic version running with one transistor before considering other higher power options.

I found having an LC meter helped when winding the torriods, but the values didn’t seem to be too critical so this was more of a confidence check.

You can see the completed LPF on the left, very compact and the instructions suggest this is good for 10w.

 

Here you can see the completed main board, with synthesiser and LPF installed. You can see on the bottom of the board the single transistor installed, with space for more.

The instructions suggest a stable 5v power supply is required for the single transistor version, and looking around the junk box I found an obsolete USB blackberry phone charger. This seemed ideal, so off came the USB plug, replaced with some wire and heat shrink. This also provided a current limited supply, with the USB charger rated at 1A being more than adequate for the TXM.

Once built, assembled and powered the kit goes into diagnostic mode (assuming no blue smoke). Mine powered up and worked without any further modifications, but any issues are likely to be mine as the kit is very well designed.

This provide the initial indication all is well, next you need to adjust the display contrast and the the PA bias.

The instructions suggest you should expect around 250mW on 10 MHz, with the power falling away as you move higher in frequency.

 

I found I could achieve 250mW with ease on 14 MHz as can be seem here on my QRP power meter.

The next stage was to get it on air, this took a little longer than expected, as getting a GPS fix indoors required some careful positioning of the patch antenna. I also found the menu system a little difficult to navigate, its not actually difficult but you have some many options its a little overwhelming to start.

I think the priority should be getting the GPS feed configure, once this is correct the display shows a heart beat. The default option is this is not configured in the software, and so even connecting up the GPS unit will not start this process. The next is frequency correction. If you have the GPS unit fitted this can be completed automatically, but you still need to setup the calibration time, and frequency correction steps in the menu.

Calibration completed showing 27.004.382 (4.382 Hz correction) and the hart beat symbol for GPS lock.

On my first attempt I had not set this up correctly, and while it was slowly correcting the frequency the number of iterations would have been extremely high before I had anything like an aligned txm.

 

 

 

I found the FAQ helpful, as this told you the specific steps to take and values to input.  I set the operating frequency to 14.0971 and after a few calibration cycles it worked!

Here you can see the unit is transmitting WSPR from JO01. The first spot I received was from KK1D at 5474 KM, not bad for 250 mW.

 

Its always nice when you build something and it works 🙂

Other suggested frequencies

Update 17/1

The TXM has continued to work flawlessly without issue. Ive move the antenna over to a dedicated 1/4 ground mounted roach pole with 4 radials. The power has been checked again and its 250 mW, the best spot I have is from 6500 KM away into Asiatic Russia to the East, and West around the same distance into the USA.

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RSGB Christmas Cumulative Contest

The RSGB have a series of Christmas Cumulative contests covering 50/70/144 and 433 MHz. The contest is a chance to put down that turkey sandwich and head out to play some radio in the winter sun. The contest run for 2 hrs, and activity is over 4 days. You can read the rules online, and activity is typically quite high.

This year I joined George M1GEO at our contest site above the Secret Nuclear Bunker in Kelvedon Hatch.

The setup included.

Icom 7100, 9e Portable Tona and RF power was provided by a Linear Amp 300w solid state amplifier. The mast was a Racal PU 12 at 5m as the band was wide open with tropo propagation, this provided some interested DX. Mains power was provided by a silent running 2KW Honda generator.

 

 

 

 

 

We managed to work 51 stations, with our best DX into Spain, EA1FDI in IN53 at 1143 KM.

The QSO map showed some great openings to the South and East.

The temperature dropped quickly once the sun set, providing a spectacular sunset and the motivation to pack away quickly. Altogether a great afternoon playing radio, with some great propagation for a change.

Thanks to everyone we worked, and all the best in 2017.

 

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Decoding HF ACARS – ARINC 635 (HFDL)

ARINC 635 is a HF data protocol defined in a document of the same name. The data is sometimes described as HF ACARS, and uses this protocol to exchange packets of data with aircrafts and ground stations over HF. The frequencies and ground stations are designed to provide worldwide HF coverage, and you can listen and decode them with any HF or SDR receiver.

I used the Sorcerer software and previously described using the program to decode other digital modes. The program provides you with decoding opportunities not available in other programs, and provides an ideal opportunity to experiment with decoding HF data. Ive also written about VHF ADS decoding, but this article deals with the HF version of ACARS.

So what is ACARS 

ACARS is the Automatic Communication Addressing and Reporting System. You can download a free VHF ACARS decode online. I havent checked, validated or used this VHF software, so at this point cant offer any further advice.

Getting started

Download Sorcerer, and select PSK then ARINC 635 as your decoder. Tune your HF receiver to one of a number of frequencies, this will depend on your location and the time of day / HF propagation conditions. In the UK I used frequencies listed for Shannon ILR and found 6.532 MHz USB as a starting point. Other frequencies are available in this article and I have reproduced the table here incase the original article goes down.

arinc_freq

Once on the correct frequency the program should start decoding.

arinc_sceen_decode

The message contents vary, but here are some examples.

———————————————————————————————————————–

[MPDU 18:40:06 GND SLOT 1,2 600 BPS ]
Ground station ID SHANNON – IRELAND SYNCHED
NR AIR CALLS 1
AIR CALL 0 = F5
LPDUS = 1
Max Bit rate 1200 bps
[LPDU UNNUMBERED DATA FM GND TO AIR HY0273]
HACARS mode: 2 Aircraft reg: UK78701
Message label: A9 Block id: D [Uplink]
Message content:-
/ESBATYA.TI2/LTBA ARR ATIS T 1820Z EXP ILS DME APPCH 05 SFC/ WET FOR RWY 05 TRL 110 BE CAUTIOUS ABOUT GP AND LOC DISTORTIONS OR INTERRUPTIONS FOR RWY 05 OR 23 AFTER VACATING RWY CONTACT 121.8 VIS 9999


The message above would indicate its directed towards HY0273 a flight shown as leaving TAS (Tashkent to Istanbul)

Others messages contain location information

——————————————————————————————————————————

[LPDU UNNUMBERED DATA FM AIR SAS150 TO GND]
[HFNPDU PERFORMANCE]
18:51:20 UTC Flight ID = SAS150 LAT 51 40 43 N LON 0 13 32 E

——————————————————————————————————————————

In this message I think its communicating what frequencies are being used / monitored by each ground station. You can match the numbers with the allocated frequencies shown in this table.

Preamble 300 bps 1.8 sec Interleaver FREQ ERR -6.403492 Hz Errors 0
17:18:16 UTC SHANNON – IRELAND DB = 49 SV = 0 GS UP LIGHT OFFSET 10
SHANNON – IRELAND UTC LOCKED Active freqs 3 5
REYKJAVIK – ICELAND UTC LOCKED Active freqs 3 4 6
RIVERHEAD – NEW YORK UTC LOCKED Active freqs 2 4

If you have any further information, additions or corrections please get in touch.

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High Altitude Balloon (HAB) tracking

Amateurs often launch HAB containing telemetry and sometimes SSTV of the ability to take and store pictures. The launch schedule is usually published online, its worth starting with this online resource. Tracking is based on an adapted version of FLdigi, this program once configured with your callsign and location will manage the upload to a central server.

UKHAS have published a beginner’s guide to HAB in the UK

You select the balloon you wish to receive and the program will configure the mode and frequency (requires CAT)

Here is an example of the data sent, the packet includes Launch name, packet number,time,location,altitude,satellites and a checksum.

SUSF,1359,11:56:28,509771791,-15067697,2594,18,140,0*C750

Its quite incredible to think you can often receive these balloons at 800 miles or more when they transmit as little as 10mW. I guess it helps if your antenna is 30 Km about the earth.

baloon2You will notice on this decode the frequency is drifting a little, probably due to the extreme temperature experienced by the transmitter. Your data will be combined with other stations, and the location of the HAB will be displayed on a map.

This is ROTIO, you can see it has some issues with GPS lock….

screen_hab

Frequency stability can sometime be an issue.

baloon

Unfortunately things dont always go to plan, sometimes the conditions are just too harsh or something fails and the telemetry stops.

 

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© 2015 Dave, M0TAZ