[greatartiste]

I can't agree more , reading this every bullsh*t alarm in my brain was triggering. In his report Mr Godfrey never mentions the frequencies used for the WSPR transmissions. This mode can be used on VHF/UHF frequencies where it may reflect from aircraft. But 95% of WSPR transmissions are on frequencies below 30 MHz and most likely below 20 MHz. These have long wavelengths and highly unlikely to be affected by an small (in wavelength terms) aircraft. If it could be affected by aircraft then Mr Godfrey would have to take into account the movement of every aircraft in that region at the time which he doesn't appear to be doing. As a note of explanation I'm a radio amateur and a WSPR station operator , its a brilliant tool for propagation studies but not for this.

[martyvis]

> Mr Godfrey would have to take into account the movement of every aircraft in that region

I'd imagine there were dozens of aircraft crossing the Indian Ocean around the time MH370 disappeared. If his technique was that good he should be able to demonstrate for any day ending in Y how he can track flight paths compared to ADS-B data from the likes of flightradar24

[fapjacks]

This would be a good rebuttal, to offer up a bunch of counterexamples of transponder data with no corresponding signal in the WSPR "data" using the same method, but also ADS-B transponders are limited in range, so there will be big gaps specifically in the Indian Ocean. But if this (frankly unbelievable) method works well enough to suss out the location of MH370 in those ocean holes then imagine how well it should work in areas saturated with transmitters and receivers. But it won't, because it really sounds like a bunch of hooey.

[femto]

I don't disagree with the triggering of your BS alarm, but don't write off the ability of frequencies in the 5-30MHz range to detect an aeroplane the size of a passenger jet. I used to be an engineer on the Jindalee Over-the-Horizon-Radar and it could detect things much smaller than this using these frequencies.

Points for and against WSPR detecting MH370:

- Jindalee uses huge power: a beamformed antenna transmitting many kW and a beamformed receiver array 3km long (yes, one of the techs who was an amateur did plug his kit into one of the arrays).

- Jindalee uses a very stable timebase, meaning it can detect small Doppler shifts.

+ WSPR has a lot of receivers and transmitters, meaning the target is illuminated from lots of different directions. With the right signal processing, these signals might be synthesised into a large aperture. Are WSPR receivers typically coherent (I/Q)?

+ According to one article, there are 5000+ WSPR transmitters [1]. If each of these is transmitting 5W (what's typical in your experience?), that's 25kW. A useable power for an OTHR radar.

- The WSPRS transmitters have a low duty cycle and are not active simultaneously?

+ By its nature WSPR will sometimes fluke excellent propagation conditions, meaning it will be able to do things that might otherwise require higher power. With a large number of stations giving N^2 propagation paths, what are the chances of some of them being useable?

+ An aeroplane the size of MH370 is quite a big target for an HF radar, with quite a big Dopper shift.

+ By its nature, a received signal will contain information about the channel though which it passed. Minus: chances are this information is filtered out by WSPR's receiver processing.

- Does the WSPR database actually store enough information to post process? Ideally it would need to store the sampled waveform from a coherent GPS locked receiver. It looks as if each record is only a received SNR and a drift (presumably a frequency offset) and a timestamp in minutes?

- Are WSPR receivers typically GPS locked, meaning they might have the ability to measure small Doppler shifts and be coherently combined with each other?

I'd put the possibility of WSPR being able to detect an aeroplane into the "intriguing" category if (huge if) it stored the necessary data in its database. It would be a computational tour-de-force, involving synthesising a large number of WSPR stations into a single aperture, then using that aperture to form bins in range, azimuth and Doppler/velocity, then tracking a target as it moves between bins. Sadly, my guess is that WSPR does not store the necessary data.

(Maybe "intriguing" is overstating it. More "wouldn't it be cool if...")

[1] https://www.abc.net.au/news/2021-05-05/malaysia-airlines-mh3...

[greatartiste]

Thanks for your post. I'm aware of Jindalee and the Russian OTHRs which claim to detect aircraft (and I believe the claim) but they are very different from WSPR.

My station transmits 10 watts (and that's on the high side for WSPR) into an omnidirectional wire antenna. Some WSPR stations use directional yagi antennas but that information isn't contained in the WSPR data. A WSPR transmission lasts around 1 minute 50 seconds but the frequency shift/signal strength is only calculated the once during that transmission (not sure if by averaging). A transmission has to start within a second of the start of an even minute. Some stations are GPS locked but I just click the PTT on my radio to start the transmission while looking at the time on my digital atomic receiver clock.

In answer to your questions some WSPR stations transmit every 2 minutes while others like mine only transmit once or twice an hour.

[femto]

Thanks for the informative reply. I think it's a fascinating system. On paper it could act as an OTHR if the signal processing was changed.

I'm guessing each station would need to lock its carrier to GPS and transmit as often as possible (10W would probably be okay with lots of stations). Similarly receiver local oscillators would need to be GPS locked (+/- 1ns?) and the receiver be coherent. Processing would need to be based on the raw stream of samples, but with a 6Hz bandwidth one could get away with a sampling rate of about 10 samples/s (Nyquist + a reality factor), each sample being a pair of 16-bit I/Q components. The low bandwidth might limit resolution. The signal processing would be the fun bit. Can all those receivers and transmitters be synthesised into one big array? Could the processing could be done in a distributed manner? Lots of interesting problems.

Apart from being an OTH radar, such a system would be the mother of all ionospheric sounders, as the main difference between a radar/sounder/communications is which features one chooses to extract from the received signal.

Is passive radar a thing in the amateur scene?