6m Aircraft Scatter

My last blog entry covered an experiment to prove that it is possible to get a straight line reflection from an Aircraft travelling away from both the originating, TX, station and the receiving station.

The Aircraft needs to be, I believe on the same bearing as that of the path between the two stations.

At my QTH this is merely a waiting game, there are so many aircraft on the S/N corridor that finally one will fit the equation.

Previous tests with G6AVK did not achieve the desired result. I think that, while his omni directional signal reached me fine, by the time it got to Aircraft sufficiently North of me it had run out of ‘steam’.
The addition at G6AVK of a mast and rotatable 6m Beam means that strong Aircraft reflections from the North are now possible.

I pointed my beam in line with the S/N UK Air Corridor G6AVK beamed toward me.
Note the trace at 19.32. There is the direct signal from AVK. A long descending trace from an Aircraft, which has passed me and is heading North, on a track at a tangent to the path between AVK and ZJO. Third a parallel trace, ‘classic’ 61Hz shift equating to an air speed of c.600Km Hour.

This produced 2 decodes of WSPR on the two frequencies.

2009-05-29 19:32 G6AVK 50.294482 -18 1 JO01ho 5 G3ZJO IO92ng 127 306
2009-05-29 19:32 G6AVK 50.294421 -25 0 JO01ho 5 G3ZJO IO92ng 127 306

I think we can now say that this is the definitive explanation of the phenomena. Repeatable by experiment, using 3 different signal sources.

More 50MHz Reflections

Whilst looking at the destruction that Aircraft Scatter (AS) can do to WSPR signals I received a puzzling series of signals decoded by WSPR from G8EUX.


The grab above shows a straight line signal 59Hz below the original signal which itself appears to be effected by AS.
This lead to G8EUX testing his TX for spurious emissions and me saying it cannot be an RX odd response due to the fact that the second signal has AS. To add to my identification as a Scattered signal I never see odd decodes from G8EUX even when signals are much stronger.

After some thought I came up with an explanation.
The straight line is AS and the other related curve is from another aircraft reflecting the fundamental signal. Being a straight line reflection means the Aircraft is moving away from both stations on a constant path relative to both stations. The Doppler shift of 59Hz thereby gives us the Aircraft speed. Which works out at 633KmHr.

One example of this phenomenon does not prove anything so I began to consider a method of proof.
Beacon GB3BAA on 50MHz lies to the South East of me, not parallel to the Controlled UK Airspace South North routes but knowing the flight paths I decided to give it a try.
Pointing my beam North away from GB3BAA I set Spectran so that the beacon was just at the top of the display, only the Morse Ident Keying, lower sidebands can be seen.
I was most interested in the minus 50 to 60Hz Doppler shift region. In a short time an example of 60Hz straight line shift occurred. There are short periods of no AS then just like buses several come at once and many with a straight line portion with a Doppler shift of 50 to 70Hz.baa-llel4.JPG

So what are we seeing? One explanation I can put forward is.
As the AS signal descends in frequency we are witnessing Aircraft travelling North away from both GB3BAA and G3ZJO and at an angle having already crossed the direct line signal path. As the Aircraft turn to cross the Atlantic there is a period when the trigonometry produces the straight line. I do not show the signal path from GB3BAA to G3ZJO. Its not critical, just think of GB3BAA as being down London way.

Equally we could suspect that the Aircraft involved could be turning earlier to take the route across via Ireland, there is an example in the animated plot doing just this, I consider the angle to be too acute for this to be the case.

si570 Synthesiser Modular MEPT Project – HF

The modular approach to the si570 Sythesiser MEPT has meant I can try out different methods. To save confusion I will not call the si570 a DDS, despite it being a handy term and it does Directly output a frequency using Digital Sythesiser techniques.

I used a Class A PA strip to get a good clean 250mW on 50MHz for multi modes.
I thought I would try the same 2N3866 Class A strip idea for a Broad Band HF PA, to get a bit more power on 24 and 28 MHz bands. I needed a little more drive so I added a 2 transistor BC184 Driver Amplifier was added too.

Right click and select View Image for full view.

Compared to the 74HC240 PA version total efficiency is low, only 12.5%. Total consumption including si570 being 4Watts, not my idea of true QRP but once you throw that Xtal away you are on a slippery slope. I quake in fear at some of the temperatures that silicon gets run at so I added a ‘Smoke Stack’ to the output transistor heat sink. Here is another view.

To the right of the ‘Smoke Stack’ is the band specific LPF at the left hand side is the band specific input filter. Both modules are easily changed over, just 3 solder links on each for band swapping.
Here we see the si570 Synthesizer, mixer and PIC WSPR, Hell and QRSS modulator.

I have run on air tests on 24MHz and 28MHz, unfortunately with no reports as yet. Future band improvements should change that soon.

Dah Dah-Dah Dah Dah-Dit Dah Dit-Dit Dit Dit-Dit

I showed a few Morse Keys on my old web site, I am not an avid collector, nor am I a Morse mode addict. However I am so glad that to obtain my Licence I had to learn the code, I would not want to be without the skill.

Recently IZ0GNY contacted me re the Bathtub Key.

Right Click on pictures and select View Image for full size.

This key was used aboard the Lancaster Bomber and had a degree of sealing against the ingress of water. My friend and fellow Ham G3JJW knows of a good reason for this, he was a Rear Gunner on a Lancaster that ditched into the North Sea. The technique for ditching and being able to escape the Aircraft which was now in danger of becoming a Submarine was for the Pilot to hit the sea hard with the rear end, thus snapping the tail end off. His ditching went to plan and he was out of Lancaster and into a Dinghy with the rest of the crew. Orange dye was used to stain the search area for rescue crews, John G3JJW thereby joined the Goldfish Club, the exclusive group of Airmen pulled from the sea looking like a Goldfish.
Whether the waterproofing of the Bathtub Key allowed any last minute position information to be sent on this occasion I don’t know.

I purchased my Bathtub Key when I was 16 Years old from a store which sold ‘Army Surplus’ it was new in a cardboard box and wrapped in many layers of waxed paper, straight from the Quartermasters stores. I still recall the smell as the wrapping was removed, wax and Bakelite. A rubber diaphragm between the Key Knob shaft and the Body soon perished and crumbled I completely removed this and the ring that secured it.

The top section hinges open after unclipping the Phosphor Bronze catch.

In contrast to the Bathtub Key is my Home Built Squeeze Key.

I sourced most of the material for this key which is based on a design in the American 73 magazine many years ago. The details were provided for it to be build of Perspex (Plexiglass). By this time my son was perhaps a little more than 16 years old and an apprentice Pattern Maker. I persuaded him and he persuaded his employer that this engineering task with so many varied disciplines was an ideal project for spare moments at work.
It took him some time but the results are superb. The rectangular Steel base does not rust due to an etching technique used. The Phosphor Bronze parts I purchased as scrap are similarly treated.

In the above picture I see I have knocked the left hand segment out of its pivots whilst moving it for the photograph. Those movable segments pivot on small Ball Bearings which are force fitted into holes in the Phosphor Bronze these locate into cups in the end of short Steel Pillars, four in all, the left and right top pair can be seen in the picture.

The fixed contact adjustable supports stand on a rod of Ebony timber. The contacts are Copper treated as the other metal parts I have never had to clean them.

The Paddles are solid Rosewood. To show his art (if you ever turn the key over) my son produced the base plate cover of Quartered solid Rosewood. The key is a piece of workmanship of which he should be proud.

Firing 100mW WSPR and other Modes at Aircraft on 6m

Three stations G8EUX, G6AVK and G3ZJO ran WSPR for more than 12Hours on 6m, 50.293MHz dial on 2 May 2009.
Apart from Spots from G8EUX of G3ZJO at 15Km there were no other de-codes. G3ZJO was RX only, the spots of G8EUX by G3ZJO have been done many times before.
G3ZJO had the advantage of continuous beaconing, multi modes, 5ele Rotatable Beam and the grabber at G6AVK activated.

Previous tests using 100mW of Slowfeld produced very useful copy at G6AVK of G3ZJO both from the direct beam heading and indirectly by beaming across the North South Air Corridor. The same beam headings were used for the 2 May tests.

G3ZJO also ran a 3 band co-linear antenna for a short time this produced the occasional burst of Aircraft Scatter at G6AVK. Peter, G8EUX produced a little WSPR and me, G3ZJO produced a short bit of QRSS.

G3ZJO could produce constant signals on the Grabber at G6AVK with 100mW to the 5ele Beam,(ERP nearer to 1Watt, I will quote RF out at the TX across 50 Ohms)constant but rarely usable due to multipath.

The most copyable signal that I observed in the test period was the Hell Ident in the following capture. 5 Unit Hell G 3 Z J swoops downward with Doppler shift from an Aircraft reflection and the O is back ‘on the line’.

Several versions of QRSS Morse and WSPR proved useless under these conditions, 5 Unit Hellschriber produced some results. Previous activity on 6m by many stations has proved to be disappointing due to multipath signals. The results using Slowfeld which was produced to exploit Aircraft Scatter provided superb communications.

RF and the Sammy Netbook

Following my recent Portable Trip when I found RF was causing the Touch Pad to Freeze. I have got round to curing the problem and giving the /P set up a test. To save writing it up twice this is what I posted on the Samsung user forum.

My Sammy has behaved faultlessly at home, used to provide coding and decoding of Digital Signals in my Amateur Radio station even when running quite high power levels.

On a recent trip to the coast I ran Sammy, Transceiver and all Domestics, (TV, Broadcast Radio, CD player Lighting, Alarm and Water Pump) on my 50 Watt Solar Panel for 4 days and Sammy came home fully charged by the Sun.

One problem showed itself on Sammy, due to proximity to the Transmitting Antenna it was impossible to run more than a few hundred milliWatts. The Touch Pad froze in the RF Field. In the absence of any other mouse it was impossible to lower the RF level once activated as the operations needs a working Touch Pad. Although most frustrating, the low power signals I could run actually made it to China, something I have not done from home 🙂

The installation used the same leads, Audio In/Out and USB to Serial, both fully transformer and opto Isolated as used at home. It was difficult to run any tests whilst away from home although coiling both leads close to Sammy allowed a little more RF power to be used.

As soon as I good get round to it I made up a shorter Audio lead and wound around 10 turns onto a Maplin QT26D Ferrite Ring. Likewise the USB Lead was passed through another QT26D with about 10 turns in all. The rings are as close as possible to the plugs that go into Sammy.
On test with the same Antenna and Portable installation on the drive at home the Touch Pad behaved impeccably at high power levels and at 10MHz and 50MHz.

I have not seen this problem on any Laptop Computers before. Due to the very low RF field involved it could explain any touch Pad freeze ups when Sammies are used in certain locations and with external leads.

Using Slowfeld for Aircraft Scatter Comms on 6m

For several years I have had an appeal on my website for a capable Ham to try Slowfeld with me.
I see from archive material that in 2007 I was appealing on the Packet Radio Network and making test transmissions anyway, just in case.
At around the same time some QRSS Knights were doing it, I was not aware of the Knights.

My previous posts show the hopeless signals on QRSS and WSPR over the 50MHz path between here and G6AVK.
Quite typical of WSPR on 6m the signals are there but the scatter is so great that decodes are rare. My thoughts turned back to Slowfeld.

What you need is that capable Ham at the other end of the path, none better than G6AVK, I put forward the idea ready for his return from a hard day at work (with overtime). While his dinner cooked the software was installed and the tests commenced.

My first transmission produced readable Hellschriber at his end.

Next I took a TX session from him.

Finally I watched my signal on the G6AVK Grabber and turned the beam so that only signals scattered from aircraft were arriving, the TX power was only mWatts.

The results are astounding when QRSS3 FSCW fails and also WSPR then good old Hell comes to the fore.

Many thanks are due to G3PTT for the software which I have tried for several years to put to use. A superb mix of modern computer methods of signal analysis and an ancient visual data mode.