Aircraft Reflections on 10MHz QRSS

Every so often a bit of Aircraft Scatter pops up on the QRSS Grabbers and causes a flush of comments. While HF reflections look interesting and make pretty squiggles I can’t remember seeing anything being done with them

The latest spotted were on 10MHz on the G6HNU Grabber in JO01ou and thanks go to Keith for the Grab I am using here and some confirmation tests we did with us both watching Aircraft Traffic on the Web and he emailing me the Grabs.

The reflections were, as I expected, from Aircraft passing the path near him at Cruising Speed and Altitude. Depending on Altitude the reflections were calculated as being initially reflected by Planes between 10Km and 22Km away from the path, the whole event taking about 30 to 40Km. Having done that the fun stopped…………Almost.

Next day I checked the Grabber to see what was happening and noticed another reflection on the signal from another station.
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Here we see at 10.139955 G0MBA the original station that the reflections were spotted on. Above that at 10.139970 G0PKT the Martelo Tower TX which also showed some reflections, then, at the bottom at 10.139905 G3LZR. Not forgetting the RX’er G6NHU we have four stations quite close together all uniquely placed with a Heathrow to EU corridor passing overhead.

Seeing 3 stations displaying data Triangulation came into mind, Whilst 6 Char. QRA’s are not very accurate I had the Loc. of HNU, PKT is easy to spot on Google Earth I could find no information for MBA but a search for LZR revealed a Post Code, better than a 6 Char.QRA.
So I set myself a challenge find MBA 100Km away from me by use of the Aircraft reflections. I brought up a map of the area. Again it’s a big picture.

I had to use the middle of HNU’s square, error will enter here but who cares when needs must. I drew a line Yellow to show the HNU-PKT path and a Red line for the HNU-LRZ path. I calculated the distance traveled by the Plane between the 2 paths using an average speed of 600Km h error alert again but we were not looking at the Aircraft information at 6.00AM.
There is only one Aircraft path that will fit that distance, the Orange line.
Now its simple to draw the Blue line which must intersect the Aircraft path at the point where the calculated distance from PKT-MBA and MBA-LZR is measured, error alert these figures didn’t exactly add up to the total but it was near enough. MBA must therefore lay somewhere on the Light Blue extension of the line. I posted my conclusions and HNU came back with his actual (South of my middle of square guess) location and that of MBA. From the new location of HNU (the one with no Callsign near it) I drew new paths in the same colours and the new Aircraft path that fits in Green , the Blue line I could end in the centre of the pale Mauve circle because now I knew his location.

I was amazed at the accuracy of my original estimate, within 2Km of the target despite the known errors. Tony G0MBA thought this was cool being DF’d by Aircraft reflections, I told him that we can now dispatch a Squadron of Lancasters on a mission to deny his soldering capability.

Ultimate2 Multimode DDS MEPT v.2.02

The Ultimate v2.02 chip was released and I had the chance to Beta test it.
Current release is v2.02a if you have a U2 with v2.01 please, please shell out the mere £3 and update ASAP. Other band users will love you for it.

Good news:-
Gone are the transients due the software zero setting the DDS before every small wanted frequency shift. This made the signal socially unacceptable, the Gentlemen operators of the past would have turned in their graves to have heard the clicks which sounded on air like someone banging a spade with a hammer.

Sorted is the linearity of the frequency shift which went awry as the band frequency got higher and caused WSPR to produce non decodeable signals. The linearity correction has also made Slow Hell Mode clean and readable.

Gone is the broad band interference which wiped out Radio 4FM on 93.3MHz when the U2 was TX’ing on 7MHz.
Gone are the bands of interference which wiped out 6m (50MHz) when the U2 was TX’ing on 28MHz.
These were the major bugs which kept me off the air with the U2.

WSPR-15 Mode has been added, also some ergonomic improvements in menu settings and cosmetic updates.
Results have been good on air, Power Output using just the one supplied Output FET at 474KHz is 250mW, I tried WSPR15 on that band and it works fine one report from 127Km was -40dB.

The Power drops as the frequency rises to give 109mW on 18MHz, at 28MHz efficiency seem to go back up a bit and 190mW is measured. I consider 28MHz to be the upper limit of operation.
All modes were found to work fine across the bands.

Bad News:-
The GPS facility which worked perfectly I though on v2.01 with my Trimble GPS Module totally fails on v2.02. Actually on re checking with v2.01 the time is always one second faster than UTC.
Using v2.02 the system time gallops on in 2 second leaps and soon is faster than real time. The 1PPS Frequecy control does not work.
Some GPS users had problems with some GPS Modules on V2.01 and some parameters were changed in an attempt to accommodate those. As far as I can tell only 2 Modules now work, which worked previously as well, and the Trimble lost out.
The GPS facility was the clinching factor on buying the kit for me and its a real let down to have it fail.
The utilisation in code of GPS Data is something I have never done, however I do note that the $GNRMC Position Data used in the U2 contains the UTC Time of the Position Fix. It is known that this time can be 1 or 2 seconds late. If one sets the system time from this Data then clocks that with 1PPS the next Data read may well be different, giving rise to erratic time keeping symptoms experienced by me and others.
It would appear that different GPS Modules have various accuracy levels and I would guess from my limited study that the better accuracy ones have a shorter PPS pulse time. No doubt that given a particular set of parameters a compromise can be achieved. I do hope a setting for diverse modules can be attained.
From my study I have concluded that the correct way to deal with GPS time is to read the $ZDA Data which is the correct UTC Time then clock that with the 1 PPS, when that Data is read again the two will agree and time galloping in 2 second leaps would be impossible.

The U2 generates noise on RX because when it is not TX’ing, the DDS is not disabled, it actually is working away on 6.25MHz doing calibration tasks, this signal is output to the PA and the PA power is still applied, Key Down being by gating the FET Source to Ground. Signal leaks out via the Drain Load to the Antenna socket.
This situation is disturbing to me, I have never had such a noisy sprog ridden shack, several times during testing I was caught off guard and confused by the spurious signals both on RX and TX.
There are some odd effects also reported by another Beta tester of pick up from the U2 via its own leads, I couldn’t improve this using decoupling, earthing changes or anything. This can manifest itself with 50Hz and 100Hz sidebands on WSPR when monitoring your own signal.
To be fair the crud, S2 on 28MHz, is not devastating but as a QRP RX station as well as TX I take great care to get as low a noise floor as possible. I complain bitterly about my neighbors Plasma TV’s the U2 competes from within.

Finally:-
The U2 has earned a place in the shack and Ultimately, pun intended, as a portable MEPT with GPS. Hence it also earned a box and it is off the bench.

It is interesting to see the Enclosures used by various assemblers of the kit. They have been of all types, ranging from large and roomy with a bit of spare room for a few sandwiches and a flask as a picnic portable to solid Die Cast Boxes which would fend off a WW2 Tank attack and some small, compact jobs too.
I went for small, compact, light weight, Hand Held with the 5Volt Regulator inside, I wanted to avoid having the LCD display fixed through the front panel and worked on avoiding having its fixing screws, which are in an odd 3 screw configuration showing. The Data Entry buttons can be quite awkward if not ergonomically arranged I mounted them for modern two thumbs use and it works out well.
The DDS has an LED indicator I didn’t add another panel LED with extra current consumption, I have a spy hole in the front panel which shows the DDS one, a light pipe will be a nice addition for that.
Band changing requires a swap of the plug in LPF. On the bench I found this quite awkward to get at, in the box the PCB is mounted so as to present the LPF at the top right hand corner, open the front and it and the PA transistors are looking at you, it is easy to hook a couple of grubby finger nails underneath to remove and change.
Input and Output, Power, GPS, and Antenna Sockets are on the rear.

Here is the U2 Boxed on Video sending WSPR on 28MHz.