Backscatter Radar

[VK3OE]

I have developed a backscatter Radar for Amateur use. This radar uses a chirp of 500Hz to 2500 Hz over one second which can be easily generated by Spectrum Lab. Simulation of the processing gain shows 36 dB available for a one second chirp with a further 17dB available after one minute of averaging. This means 56dB of processing gain available which for a signal 46 dB below the noise will produce a 10dB signal after one minute.

I have been conducting some test with David VK3AUU with me transmitting and David Receiving. We turn our beams so as to minimise the direct signal. David records the signal in Spectrum Lab and sends the WAV file via email. I then process the signal in Matlab and plot the result.

On 8 Jan we tried and received a high level bacscatter return form 800km but no other returns were evident. At 06 UTC today the propagation seemed interesting so we pointed our beams at 60 degrees and tried with 5 one second chirps. On processing the return I was astounded to see a return at 13500km but did not believe it. At around the sanme time Wayne VK4WTN poped up to say he was hearing US stations. Thus here is the verification and a suprising result. The return signal is very large but that may not be to unusual because of the size of the reflector.

More testing is now required.

I will post the pictures of the radar returns when I can work out how to do that.

The matlab code need to be converted for general use so I will look at how to do that.

This may be the technology to replace beacons and TV transmitters, time will tell.

Andrew Martin
VK3OE.

[VK3OE]

A further Note..

Because I use a chirp I also get range information with about a 12.5 km per range gate.

The system is basically a mini JORN radar and requires stable transceivers with a computer and sound card.

A station about 60 km away is also required for the receive as the direct signal would otherwise overload a local receiver.

Andrew
VK3OE

[VK3OE]

Here are the pictures...

[VK6OX]

Hi Andrew,

What cxr freq are your VLF chirps riding on?

This could be an exeriment worth progressing.

73

[VK3OE]

Hello Andy,

Sorry, I did not mention that the chirps are on 50.160Mhz using a 756P3 transmit and an IC706mk2G for receive.

Andrew VK3OE

[VK6OX]

Thanks for that Andrew,

I suspected of course that you were using 6m somewhere!

It would be great to be able to run a "VLBI" type experiment (several stations across VK) but unfortunately 6m at present is not in a condition for us to do so.

Please keep us posted on your progress.

73

[VK3OE]

Hello Andy,
Any other band could be used to see where the propagation is open to. HF and VHF bands can easily be used. I will try out some experiments on these bands as well.
Best regards,
Andrew VK3OE

[VK3OE]

Hello,
David and I just tried out the radar pointing South as we both have good take-offs in that direction.
Nothing was received using the same systems as earlier.

This is a good verification that there was nothing within our system that could have caused the result, so our system is working very well.

See South Result picture.

Andrew Martin
VK3OE

[VK3OE]

Hello all.

I have done some further processing of the backscatter radar signal to see if the was possibly a long path signal from the Texan station calling towards ZS at around 06UTC Thursady 21 Jan. The beam heading David 3AUU and I happened to be using was 60 degrees so there is a possibility that Wayne VK4WTN did hear something on the long path.

The result shows and additional but small return at 7dB above the noise on the long path at a range of 27,000km which corresponds the the US west Coast. This would have been of the back of our beams and the long path signal is 30dB below the short path signal. This 30dB difference could correspond to the combined front-to-backs of our beams +-. In a subsequent test pointed South using the same system there is no evidence of any signals at these distances.

There was probably more going on Thursday around 06UTC that we might have previously thought.

30,000km range picture below.

Andrew
VK3OE

[VK3OE]

Vertical scale above is dB I should have marked the scale.

Andrew
VK3OE

[VK3OE]

Hello,

Here is the backscatter at 60 degrees at 0010 UTC 22 Jan 10. VK3OE transmit, VK3AUU receive. 50.160MHz. 3 one second chirps.

The direct signal is at 0 km, the backscatter is from between 1000 km and 2000km due to the Es.
This entirely consistent with the vertical sounding at Sydney for Today.

There is also a small signal at 7400km.

There is nothing at 13500km as occurred yesterday.

Verification is proceeding very well, no issues are showing up which would invalidate the system.

Andrew
VK3OE

[VK4MDX]

I really like this. Not sure how difficult it is to set up, but I envisage pairs of radios all over the country doing this

[VK3OE]

Hello,

So here it is, the probable means by which a contact was made today to A35A, 4 hops Es.

Given earlier tests this has a good chance of being correct.

Andrew Martin
VK3OE

[VK4TS]

Absolutely Brilliant Andrew - a credit to you and your team..

The expansion of the concept defies imagination - internet netting of transmitters and receivers for an Australia wide radar...well done guys I feel I am witnessing a breakthrough moment in ham radio

Trent Vk4TI

[VK3AUU]

For those interested. This is the receiving antenna.
15 elements on 24 metre boom
14 dbd gain, 29 degree beam width in azimuth
Receiver is ICOM 706 MKIIG

http://i962.photobucket.com/albums/ae10 ... 20Yagi.jpg

[VK3OE]

Hello,
Here is the latest record taken from 320 degrees.

The Es returns are evident but the 1000km return seen previously is not evident, indicating possible trapping by the E layer.

I do not know where the small returns around 6000km are from or where the 7300km return could be from. Maybe we need more directional antennas.

Andrew
VK3OE

[VK4XA]

This is a very interesting development indeed Andrew, I will watch this thread with interest.

[VK3OP]

Congratulations Andrew !

I have been eagerly awaiting the results of your FFT results of the tests conducted with David.

This could revolutionise the way we analyze band propagation, its a pity I am too close to you to help in the testing.

Cheers

Frank VK3OP

[VK2ZRH]

Well done Andrew and David.

The above record (22 Jan 2010 0550 UTC 320 degrees) is both intriguing and instructive.

The prominent echo at 7300 km is likely to be from afternoon (or supermode) transequatorial propagation (TEP) - two reflections from the F-region equatorial ionosphere anomaly (EIA) without intermediate ground reflection, over a path of about 5000+ km. That is, the classic "chordal hop", dubbed F-F (whereas two F-region hops is 2F). Reaching this circuit then would likely have been by the Es hop shown at 2100 km. So, we have TEP extended by Es - also known in ionospheric circles as "mixed mode" propagation and dubbed Es-F-F. And here we are in the midst of the solar cycle doldrums

The reflection at 3200 km ("reflections" around 3000 km ?) has me intrigued. Could it be a single F-hop, two 1600 km Es hops (in which case, where's the 1st reflection ?), or propagation "trapped" between two Es clouds, one above the other, for a distance ? The Canberra and Sydney ionograms aren't much help, the ionosondes being too far east of the propagation path (although both show Es). If I squint, however, I can see a bit of "lift" in the noise midway between the 1000 and 2000 km range lines.

Then there's the question of the multiple small echoes from about 5900 to 6600 km. Could they be scatter from small structures in the EIA ?

That's the exciting thing about results from new tools: they tend to throw up new questions along with answering old ones

73, Roger Harrison VK2ZRH

[VK3OE]

Hello Roger,

Thanks for the comments, the earlier event at 21 Jan 0610 UTC corresponded with som apparent propagation from THE USA heard by VK4WTN, any comments on that please.???

The other BIG problem with this type of system in its early days such as this is, is to prove that all of the effects being observed are not system defects, so the testing and checking will continue for some time. Biggest issues we have had so far are timing and frequency error but but can be fixed in software. I am also concerned about the group delay and amplitude of the transceivers that we are using and looking at a chirp trained channel equaliser. One early concern was that the second harmonic of the chirp would cause spurious echoes but as it turns out with a positive chirp, harmonics will appear before the direct signal and are not an issue.

Onwards !!!

Andrew,
VK3OE