Backscatter Radar

[VK5ZD]

Hi

Neat! Any chance the fourth 'echo' could just be the signal going right around the earth?

73
Iain

[VK3OE]

Hello Iain,

As the time base is absolute, then the first around the earth the whole way will be @ 266ms, so anything less (138ms) is only part of the way.

73
Andrew.

[VK5ZD]

Hello Iain,
As the time base is absolute, then the first around the earth the whole way will be @ 266ms, so anything less (138ms) is only part of the way.
73
Andrew.

I must be missing something...
One lap around the planet is about 40,100km which, at 300km/mS, is about 134mS per lap. No?

[VK3OE]

Hello Iain,

As the radar goes there and back the velovity is effectively half, so 150km/ms.

73,
Andrew.

[VK5ZD]

Hello Iain,
As the radar goes there and back the velovity is effectively half, so 150km/ms.
73,
Andrew.

Which gets back to my original question...
A signal takes 134mS to go half way round the planet, reflect off something and return to the receiver.
A signal takes 134mS to go all the way round the planet without reflecting off anything(*) and arrive at the receiver.
How do you distinguish between the two?

73
Iain

(*) Ignoring the normal 'skip' process.

[VK3OE]

Hello Iain,

Well, after a bit of navel gazing, I now think that you are correct.. !!

On considering the width of the return signals, it is probable that they are not backscatter as I first thought. In previous long distance measurements the width of the backscatter signals is quite wide, much wider than the signals at 138 and 277ms.

The fourth echo is almost exactly half of the time for the fifth echo, unlikely if it was just backscatter. So we have two bits of evidence that point to the fourth echo being once around and the fifth echo being TWICE around, just as you postulated!!!

Given that the transmit antenna is a vertical wire and the receive antenna a two element yagi, then is is also possible that a signal comming in the back of the yagi will be easily seen.

Even using antenna discrimination will not work very well as once around in one direction is just as likely as once around in the other direction given that the transmit antenna is the vertical wire.

Going twice around is rather interesting as I got the same result on 21MHz at around the same time with the same delay values, but not on 14MHz.

The little extra time of 5ms (assuming that the earth surface distance is 40075km = 133ms) could be accounted for by the ionospheric path at the circumference of the earth at the F layer height. If an F layer height of around 211km (average) is assumed then the 138ms is very close to the actual F layer distance of 41,400km if the signals travel by the F layer around the earth. If correct then this is pretty amazing (errors allowing).

The signal level difference between the first around and the second around is just -15dB, a bit more power and I should see three around but in the trace from yesterday the second around is just +12dB above the noise so third ariund would be at -3dB, not visible!!

Given that the first echo is at 3150km, it is most likely that all of the propagation is via the F layer. If close in Es was involved the first echo would be around 2000km.

Thanks Iain

Some more work required..

73,
Andrew.

[VK3OE]

Hello,

And the same result again today on 21MHz. beaming 300 degrees, 41550 once, 83100km, twice.
On 28 MHz, only once around at 41400km.
0n 14MHz only once around at 41,550km.

73
Andrew.

[VK3OE]

Hello again,

Today on 28MHZ once around (41310km) and twice around (83190km) @ 90 degrees. There is also an Es link at 1500km but that is fading fast. There is a -20dB difference between first around and second around so path is a bit more lossy than earlier result.

28MHz

On 21MHz, once around (41400km) and twice around (82950km) @ 90 degrees. There are Es and F links in close (all the way out to 9000km).

21MHz

PS, For the backscatter signals the distance is 150km/ms, for the round the earth signals the distance is 300km/ms.

73
Andrew
VK3OE / VK3OER

[VK3OE]

I can now confirm that I have been able to verify that the signals as measured by the chirp radar do go around the world twice on 28MHz.
I have built a 3 element yagi for transmit so that I can now transmit East (VK3OE) using 50 watts and receive on a two elemnet Yagi from the West on the remote (VK3OER). This configuration produces the highest long distance signal levels from the West thus confirming that the signals have gone around. If I point the receive antenna in the same direction as the transmit antenna then the long distance signals at 41500km and 83000km are lower in level by at least 10dB.

The most interesting aspect of the first and second around the world signals is that there is no additional increase in signal width for the second around compared to the first around. This indicates that there is one dominant mode that forms before the signal has gone around once and that all other propagation modes are probably suppressed by the time the signal has travelled about half way around. The other interesting point is that the signal scatters out of the F layer at the first and second around indicating that the F layer is wavy. If the F layer was not wavy but flat (mirror like) then the first and second around would signals would not be received at all.

I have attached a picture of a twice around the world result with the correct distance scale. (Processed using MATLAB)

28MHz twice around

The direct signal is the first signal at about 200km. The second signal at about 7000km is twice its actual distance as it is an Es signal and is measured by backscatter. I have scaled the distance for the around the world signals at 300km/ms while the backscatter signals are scaled at 150km/ms. Thus the first backscatter return is actually at 3500km.

I have also measured 7 hops of Es in a direction of 60 degrees, out to 10,950km. (From Spectrum Lab). This is 1564km/hop which from the result is about correct. The fact that 7 hops show up is excellent evidence to show that propagation to North America can be via multihop Es ONLY. This is also probably the case for the Northern hemisphere summer whereby multihop Es could be the dominant mechanism for EU to NA 6m contacts. This is maybe the first direct evidence that multihop Es is the mechanism and not the SSSP modes using a combination of Es and F that is the current theory. There is also probably some sort of Es mode cahnge after the first two hops as the amplitude decreases by about 20dB for hops 3 to 7. The amplitude of the backscatter for 3 to 7 is also very similar indicating that the forward and backscatter signals do not suffer very much loss from hop to hop. (more at GippsTech 2012)

7 Hops Es to 10,800km.

First signal at 450ms is backscatter from an aircraft, direct signal is at 467ms. Next 7 signals are probably Es backscatter out to 10,950km( range rate is 150km/ms ). The signal at 603 ms is the first around the world of the back of the receive antenna (distance is 603-467=136ms. Range rate is 300km/ms, distance is 40,800km).

73
Andrew
VK3OE / VK3OER

[VK2ZRH]

Well bloody done, Andrew!

73, Roger Harrison VK2ZRH

[VK5PJ]

Andrew,
when do you find time to sleep? looking bloody good, now all we need is the HPSDR group to decide on a hardware spec for a compact sounder?

Regards
Peter. vk5pj

[VK3OE]

Hello Peter,

I am reliably informed by Phil Harman (VK6APH) that the HPSDR hardware with the operating chirp modes is nearly in production. There is also a PC application for the chirp decode. (see the HPSDR pages). There is also the possibility of a small LINUX based processor for signal processing and a GPS module and 100W PA pin switched so that the radar can be operated in monostatic mode. I am also informed that many chirp modes are already programmed in so we wait with great interest. As this system is GPS locked it can also be well used as a beacon and provide a direct reading distance. Phil has programmed in the beacon ID capability using coded forward and reverse chirps. The possibilities are most interesting.

I am now also speculating how good an early warning is provided by the 28MHz radar signals as an indicator for 50MHz. There is of course a much lower probability of 50MHz openings that 28MHz openings but given past experience in previous sun spot cycles when 28.885 was widely used as a liason, this idea looks very good.

Roger may be able to comment further, please?

73,
Andrew.

[VK3OE]

Hello,

I have updated some of the comentary on the twice around the world result and the 7 hops Es (see the results in an earlier post). A few more ideas have come to me in the last week so I thought that it would be worthwhile to share them.

I am also in the process of further observations so will post them if anything interesting turns up.

73
Andrew
VK3OE / VK3OER

[VK3OE]

On 14 June I posted a result showing 7 hops of Es out to 11,000km.

In the most recent publication of GippsTech 2011, pages 91 to 123 Roger Harrison has an very extensive paper on Es " Sparodic E - MUF Myths, Summer Solstice Short Path Propagation and Forecasting Openings". This paper is well worth a read!! My particular interest here is Roger's description of SSSP (page 111 to 118 ) where he reports after much analysis that "The remaining option is that SSSP propagation is supported by multi-hopEs, nEs, Figure 25. The next step is to find the evidence to match the contacts."

So, The measurement of the 7 hops Es from the radar is indeed the evidence needed to show that summer solstice short path propagation is dominated by multi hop Es.

This is excellent news as it indicates that there must be many opportunities for long distance Es contacts on 6m, many more than previously suspected.

So, I could say if Es is around, forget the local contacts (VK) and look further out. 110 to 150 is much more important if this multi hop Es is as common as it seems to be. Good antennas and good operating practices will be rewarded!!!

73
Andrew
VK3OE / VK3OER

[VK3OE]

Hello,

Here is a radar trace for 28MHz, 0430UTC, 2 August 2012, transmit 80- receive 260 deg. averaged 64 times, processing gain = 54dB

Trace shows out to 2nd F hop plus twice around. No Es showing so no possibility of 6m linking to F, nothing on 6m from the radar.

28MHz, 0430UTC, 2 Aug 2012, TX 80 - Rx 260 deg

Here is the CW skimmer spectrum showing the direct and the first around the world signal delayed from the direct.
This indicates that a CW contact could be made under these conditions although the S/N is very low and would push CW skills a bit, but achievable.
41,000km on 28MHz!!! Would need antennas to be side on to get direct signal to the noise.

CW Skimmer Spectrum showing direct and first around the world signals.

73
Andrew
VK3OE / VK3OER

[VK2ZRH]

Blaaardy hell, Andrew. Brilliant stuff !

73, Roger Harrison VK2ZRH

[VK3OE]

Hello again,

Here is the latest effort with the backscatter radar, three times around the world on 28MHz.

Three times around the world on 28MHz

There is about 15dB loss between each around the world signal indicating that the loss is linear with distance (not square) which indicates that the signal is guided in one plane.
There were very good openings to Europe at the time of this measurement which followed a proton event.
Now all I need to do is to get 6m to do the same.
It also shows that a 41000km contact on 28MHz could have been possible also.
Here is the CW Skimmer picture also showing three around the world signals, the third around the world is just visible in 6 of the chirp traces.

CW Skimmer Showing around the world chirps.

The first trace is the direct chirp signal (one second chirps of 500Hz to 2500Hz) while the second trace is the first around the world signal. With beams side on (to remove the direct signal completely and pointing 150 degrees and 330 degrees the CW Skimmer traces indicate that a CW contact could also have been made on 28MHz over a distance of 41,000km, the longest possible contact.

Transmit was from VK3OE at 150 degrees, receive was from VK3OER at 330 degrees.

Andrew.
VK3OE/VK3OER

[VK2ZRH]

Phe-bloody-nominal !

Next trick - four times

You'll probably need a 5-over-5 LFA Yagi array at Harcourt and a bit more wick at Ferny Creek

Keep it up, Andrew

73, Roger Harrison VK2ZRH

[VK3OE]

Hello,

Just in case anyone wishes to follow up on how this chirp radar works and some of the results achieved, I have published an article in AR for December and a slightly shorter version in DUBUS 4/2012. I look forward to you questions.

Good reading when there is no nEs.

73.

Andrew.
VK3OE/VK3OER

[VK3OE]

Hello,

At its AGM on 20 April the RSGB awarded the Wortley-Talbot Trophy jointly to myself and Phil Harman "to recognise outstanding experimental work in amateur radio" for the work on chirp modulation.

This award is indeed a great recognition by the RSGB for the chirp work and Phil and I are very honoured.

Andrew
VK3OE/VK3OER