Backscatter Radar

[VK3OE]

Hello Ben,

As to the HSPDR project, you should have a look at the new GRIFFIN project, this project will include the capability for a chirp beacon and is proposed to have a 5 watt output, sufficient to drive a class C amplifier. The details are still being finalised, there may be a web interface through which the GRIFFIN can be programmed on a wide range of frequencies as well as call signs etc. so that it can be used as a drop-in exciter for existing beacons. The chirp mode will be time and frequency locked. see..
http://openhpsdr.org/wiki/index.php?title=GRIFFIN

There is also the possibility of a standalone application for a chirp receiver (receiver + sound card + PC) that will also be time and frequency locked. This would make a great companion for the GRIFFIN exciter. The GRIFFIN exciter could also be used in the home station for radar experiments.

I will keep this forum up to date as I get more information.

As to the UHF propagation mechanisms, you shoul check out my paper on VHF/UHF/microwave propagation as published in the
International Microwave Handbook, 2nd edition, pp37 to 47.

Andrew
VK3OE.

PS.
I will send you a dB scaled picture of the some of the Es results.

AS

[VK2ZRH]

Sean, VK1FMSY

Send me an email: rogerh at internode dot on dot net

I'll send you a PDF of my presentation.

73, Roger Harrison VK2ZRH

[VK3OE]

Hello Again,

I have now got a good remote site going 145 km from home (VK3OE/p). It is solar powered, and is at a height of 572m. I use the Telstra 3G for connection. I also use the remote rig devices for voice and control.

Here is one result from today showing the returns from 45 degrees @ 3000km, 4500km and 5250km.

I have also included a picture of the remote site.

73
Andrew
VK3OE

[VK2ZRH]

Far out !

Well done, Andrew.

73, Roger Harrison VK2ZRH

[VK3OE]

Thanks Roger,

It has been a long time coming but, the results speak for themselves.

I can also see meteors and aircraft, so far, now for the UFO's!!!

73
Andrew
VK3OE/p

[VK2ZRH]

Very good, Andrew.

BTW: what was the UT date/time of the radar return ?

73, Roger Harrison VK2ZRH

[VK3OE]

02:45 UTC Roger,

Should have put that in the original, all got too exciting!!

I also obtained the relevant maps at that time which make interesting viewing.

There was also some evening contacts from VK8 to KH, the radar showed echoes from close to the geo equator at that time as well.

I have a word doc with many of the results and data so could forward if interested Roger. Send me an email seperately please.

The Radar is not getting any returns from North (JA) as the transmit site does not have a very good horizon in that direction. All other directions OK for transmitter and receiver.

73
Andrew
VK3OE

[VK2FAK]

Hi all....

Just curious....is this project still running ....if so, how is it going...

John

[VK3OE]

Hello John,

The project is going very well, The Griffin project is in Beta test, The HMI is also working rather well. I received an update from Phil Harman just last week.

Griffin GPS locks to within a uS of UTC, and all the chirp coding and decoding is working. First application will be a 100W chirp beacon in WA pointed towards Reunion Is on 2m.

There is a lot of interest out of the USA especially 6M operators who are worried that as the TV CH0 transmitters are turned off then there will not be any more propagation indicators.

Griffin suits this exactly as it will be able to be run as a monostatic radar as well. I expect Griffin prototypes for the chirp radar may be available within 6 months.

Andrew
VK3OE

[VK3OE]

The ongoing excellent development of the chirp radar and beacon project is reported on here:

http://www.fotogravett.com/Docs/The%20C ... beacon.pdf

by Phil Harman VK6APH.

This is a highly recommended read and shows the current state of development as well as canvasing some of the future potential.

It is getting very exciting and will provide an entirely new avenue for amateur experimentation with an any band radar and beacon with very high power, gained through signal processing.

My dream come true, and an opportunity to express my great grattitude to Phil and the HPSDR team for their work.

PS, just in case the link above does not work the last part of the URL is : /Docs/The%20Chirp%20beacon.pdf

73,
Andrew
VK3OE

[VK2FAK]

Hi all...

Had a read of the Pdf and found it very interesting.....keep up the good work..

If I read correctly you have a possible -50db S/N but you will use -30 so your Beacon can have an callsign ID on it...

It seems a pity to have lost much of the benefit just for an ID, yes I understand its a legal requirement but could you not say have the ID timed so it was only sent at the max time limit to stay within the radio act...say once every few minutes or so, while the rest of the time your taking full advantage of that nice -50db S/N...?...


seems strange there is not more interest from the locals here.....

John

[VK6APH]

Hi John,

You are correct. The -50dB comes from integrating the output of a matched filter for 60 seconds. Once you integrate you remove the ID data so in order to ID you have to look at the output of the two matched filters (one for forward and the other for reverse chirp) before the integrator so you can read the ID. We intend to only ID when required so most of the time the -50dB holds.

Andrew pointed out today that in fact we gain an additional 3dB with Mercury since we are processing a complex (I & Q) signal. Additionally, by adding Forward Error Correction code we should be able to read the ID at lower than -30dB S/N.

In practice you will be able to 'see' the beacon at -50dB S/N (i.e. an early warning) but have to wait for a futher lift in order to get a positive ID. By then you will have positive ID in regards the frequency and range but not have decoded the call sign. I guess we need that last step to comply with the 'rules'.

I also had a comment that we are using a lot of bandwidth. That's true, and how we get the system gain, but you could have multiple chirp beacons spaced say 10HZ apart and you would be able to identify each one individually.

Andrew sure has started something rather exciting

73 Phil...VK6APH

[VK3OE]

Radar Operations.

For the first time it is now possible for amateur radio operators to contemplate using a propagation radar while operating entirely within the existing regulations. The radar discussed here operates using a chirp. This is a linear FM modulated carrier with bandwidths from 2kHz to 100kHz depending on the frequency of operation. The 2kHz radar can be achieved using the Spectrum Lab software. The wider bandwidth radar system is being developed by the HPSDR group and Phil Harman VK6APH is leading this development. Of course, the normal requirements for signal identification remain and can be met by sending a CW identification at appropriate periods.

The signal processing gains available from the chirp radar are sufficient to allow investigation of propagation on all amateur frequencies. Of particular interest in the present sunspot cycle is 6m propagation. On this band propagation is very fickle so it would be nice to know where it is open to without the need to resort to beacons or TV carriers.

The great advantage of using the amateur chirp radar is that outstanding results can be achieved with transmitter powers and chirp bandwidths that are entirely within the existing regulations. Further, because a large surface area is illuminated by the transmitted signal when it returns to the earth surface, very high reflection gains are possible, gains that are far in excess of what could be achieved by a normal amateur antenna. This makes the chirp radar easily useable within any of the amateur bands.

When using the chirp system in radar mode two modes are possible, bistatic and monostatic. The bistatic mode uses simultaneous transmission and reception which means that the transmitter needs to separated from the receiver by some distance to prevent overload of the receiver. For amateur operations this means that the receiver is typically 60 to 100km distant from the transmitter. For this mode the receiver is operational when the transmitter is transmitting with the result that because the receiver is not overloaded long transmit pulses can be used and the minimum range is not compromised.

The monostatic mode uses a co-located receiver and transmitter which means that the receiver needs to be muted when the transmitter is in operation so as to prevent overload. In order for the radar to have good close in range only short transmitted pulses can be used otherwise the minimum radar range is too far away for the radar to be effective. This also means that the minimum radar range is set by the receiver muting time. Further, to get sufficient gain from pulse averaging in the monostatic mode, as many pulses as possible should be sent which indicates that the maximum range is set by the receive time and the repeat rate of the transmitted pulse.

Of course the great advantage of monostatic operation is that it can be run from one antenna, the requirement of course being that the transmit-receive change over must be very fast, a relay changeover is not fast enough.

The Table 1 sets out some of the possible modes of radar operation together with the operating parameters and gain achievable for both bistatic and monostatic modes of operation. The bistatic mode uses long transmit pulses (one second) while the monostatic mode uses short transmit pulses with much more averaging to achieve the indicated gain. As the chirp band with is increased the processing gain also increases and the resolution improves.

The greatest gain is achieved by the bistatic radar (separated transmitter and receiver) when a one second, 100kHz chirp is averaged over 60 seconds. The resolution, minimum range and maximum range are also the best achievable. This system could easily be used for moon bounce as the echo will return in a later receive window. For 2m moon bounce, a low power transmitter (10 watt) could be used with a receiver that was say a few km away from the transmitter, transmitter and receiver using 11dBi yagis. The received moon echo will have a S/N of around -60dB in a 2kHz bandwidth with such a system. If a 100kHz chirp is used such as previously outlined, the S/N at the output of the chirp receiver should be around +21dB after a one minute averaging time.



Type, Bandwidth, Tx Pulse length, Repeat every, Min range, Max Range, Resolution, Processing Gain (60 seconds)
Monostatic 2kHz 5ms 100ms 1500km 13500km 75km 41dB
Monostatic 16kHz 5ms 100ms 1500km 13500km 9.5km 50dB
Monostatic 100kHz 0.3ms 10ms 70km 1350km 1.5km 56dB
Monostatic 100kHz 5ms 100ms 1500km 13500km 1.5km 58dB
BiStatic 2kHz 1sec 1sec 100km 75000km 75km 54dB
BiStatic 16kHz 1 sec 1 sec 100km 75000km 9.5km 63dB
Bistatic 100kHz 1sec 1sec 100km 75000km 1.5km 71dB
Table 1. Possible chirp radar operating modes with averaging gains achieved after 1 minute, the processing gains are referenced to a 2kHz bandwidth.


For monostatic operation either a 5ms or 0.3ms transmit pulses are used, the 0.3ms pulse is able to provide a 70km minimum range and a maximum range of 1350km. This is intended to be used where short distance radar measurements are required such as for investigating tropospheric propagation. The 5ms pulse is for investigating greater ranges but has a greater minimum range.

With the existing regulations in Australia, up to 8kHz bandwidth can be used on any amateur band above 1.8Mhz, while the 16kHz bandwidth can be used above 28MHz, and the 100kHz bandwidth can be used above 50MHz. Above 432MHz the bandwidth is not restricted except by the bandwidth of the respective bands, thus providing a great opportunity for experimentation with a very wideband chirp radar or even very wide bandwidth beacons.

Andrew,
VK3OE/VK3OER

[VK4OX]

Andrew,
This is setting alarm bells off with me. If every-one starts chirping with 100kHz bandwidth, how are we going to hear anything in the weak signal segments of any band above 50MHz?

i trust that no chirp radar will be operating below xxxx.700MHz on any amateur band.

Adrian. Vk4OX.

[VK3OE]

Hello Adrian,

In 2kHz bandwidth there is not an issue.

For the 100kHz mode there could certainly be a problem if chirps are used below XXXX.4, not too sure about XXXX.7. Several states have restricted access for the moment to 50MHz, so a little care is needed there as well.

It will be another mode for development of the various band plans, I do not believe that we should not use the chirp just because it is not in any current band plan.

It is a significant advance in the tools that we have and should be treated as a great new opportunity, and with care.

Andrew
VK3OE/VK3OER

[VK4OX]

Andrew,

This thread is listed under Digital Modes, I have no issue if the bandwidth of the chirp radar is 2kHz. The Australian Band Plan 2010 lists digital and packet radio as being above xxx.700MHz on any vhf/uhf band. There are many traditional beacons in the xxx.400 to xxx.600MHz segments.

PLEASE, no wideband transmissions of any type below xxx.700MHz of any vhf/uhf/shf band.

73, Adrian. VK4OX.

[VK3OE]

Hello Adrian,

It is quite simple realy within the existing band plans.

It is not strictly a digital mode, rather a wide CW mode, could be treated as "other".

Use 50.32 to 52.0 VK5,6,8,9,0 assigned to all modes so no issue there except VK1,2,3,4. For the moment VK1,2,3,4 may have to use limited bandwidths, say 50.22 to 50.27 until CH0s are off then above 50.3.
Use 145.225 to 145.775 assigned to all modes so no issue there.
432.625 to 433, reserved at present but could easily go there without any issue.

In HF bandwidths are more limited and also the path loss is lower and there is no great need to use wide bandwidths.

No issues.

73
Andrew
VK3OE/VK3OER

[VK4OX]

Andrew,
That is re-assuring. Make that 432.700 and above and I'll be happy. Thank you.

73, Adrian. VK4OX

[VK3OE]

Here is what the backscatter radar returns look like for 06:45 UTC today @ 45 degrees. The distance is 150km per ms, the direct signal is the first signal on the left at 625ms, the next signal to the right from 630ms to 638ms (750km to 1950km) is all the backscatter.

Transmitting from VK3OR @ Ferny Creek, QF22qc and receiving at Harcourt on the remote QF23db.

Good DX

Andrew
VK3OE/VK3OER

[VK3OE]

With the higher SSN 10m has been very good. So some fun with the radar. Transmitting on 28.339 from ferny creek using a vertical wire with 50 watts and receiving on the remote (VK3OER) I have received echoes from 83,000km, twice around plus a little. A similar result was also obtained on 21MHZ but not on 14MHz. This is consistent with the predictions using HamCap for the three bands.

In the attached picture the distances are in ms and the firsit signal on the left is the direct signal which is considered to be 0km. Direct signal @425ms=0km, first echo @ + 21ms= 3150km, second echo @ +41ms = 6150km, third echo @ 68ms = 10,200km, fourth echo @ +138ms = 20,700km (correct distance is 41,400 as Iain VK5ZD points out, see later posts), fifth echo @ +277ms = 41500km (correct distance is 83,000). Signal from 83,000km is about +12dB S/N.

(above is edited to remove my earlier mistake about the around the world result, after a sugestion by Iain VK5ZD). It just did not seem possible, I have since verified the result using directional beams to determine which direction the received signal is coming from.

73
Andrew
VK3OE/VK3OER