lustyd
Well-Known Member
the aeroplanes in the Baltic? All of them looking at that tiny thumbnail of a map. Planes are high in the sky.
E-Loran
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Dockhead
Well-Known Member
Here's the math:
The basic principle is the inverse square law (don't know how many other radio amateurs may be reading this; forgive me for the basic stuff). The difference between received power from two transmitters of equal effective radiated power at 20km and 20,000km is 1000^2 = 1 million times, or 60dB.
To fully jam GNSS, you need about 24dB, although disruption starts at only a few dB. Source: https://www.gps.gov/sites/default/files/2025-06/AdvisoryMeetings_PTA-Toughen_April2024.pdf.
At 20km, you only need 0.025 watts of ERP (!!) to fully jam a GNSS signal. You have line of sight to 800,000km2 (!) of the earth's surface at that altitude. To jam a 30,000km2 area you need only 0.625 watts.
This does not account for antenna gain, but bump up to even 10 watts and you can wash that out. Considering the fact that a 100watt jammer can fit in a backpack, it can be seen that this is a gigantic problem for GNSS.
The basic principle is the inverse square law (don't know how many other radio amateurs may be reading this; forgive me for the basic stuff). The difference between received power from two transmitters of equal effective radiated power at 20km and 20,000km is 1000^2 = 1 million times, or 60dB.
To fully jam GNSS, you need about 24dB, although disruption starts at only a few dB. Source: https://www.gps.gov/sites/default/files/2025-06/AdvisoryMeetings_PTA-Toughen_April2024.pdf.
At 20km, you only need 0.025 watts of ERP (!!) to fully jam a GNSS signal. You have line of sight to 800,000km2 (!) of the earth's surface at that altitude. To jam a 30,000km2 area you need only 0.625 watts.
This does not account for antenna gain, but bump up to even 10 watts and you can wash that out. Considering the fact that a 100watt jammer can fit in a backpack, it can be seen that this is a gigantic problem for GNSS.
lustyd
Well-Known Member
More waffle to support wild conspiracy theories about disruption.
I’ll say again, anyone on British soil using jamming equipment will be found and stopped extremely quickly. That’s true of most civilised countries.
The planes in your thumbnail are above hostile territory and will suffer disruption on any radio based solution. There is nothing at all in eLoran that would change that.
I’ll say again, anyone on British soil using jamming equipment will be found and stopped extremely quickly. That’s true of most civilised countries.
The planes in your thumbnail are above hostile territory and will suffer disruption on any radio based solution. There is nothing at all in eLoran that would change that.
st599
Well-Known Member
Also, there's an assumption of LOS transmission, but L-band can have atmospheric ducting, especially over water and in high pressure weather.
Dockhead
Well-Known Member
I never had a Decca receiver (too expensive!) but I still have a Heathkit RDF set somewhere.
No one is saying that GPS/GNSS is going to go away. Of course not. But there's a pretty broad consensus around the world that alternatives are need as backups and cross-checks. It's a basic principle of seamanship to try to have multiple sources for every critical navigational datum anyway -- over-reliance on a single system really violates that.
Also, there are different ways to harden GNSS to make it less exquisitely vulnerable as it is today. See: https://www.gps.gov/sites/default/files/2025-06/AdvisoryMeetings_PTA-Toughen_April2024.pdf. This will require new equipment at the receiving as well as transmitting end, unfortunately for us. This will be an improvement, but will not prevent brute-force jamming.
An interesting fact on this -- the Russians never decommissioned their LORAN system (also China and South Korea). It's reported that they are using it on the battlefield in Ukraine amidst widespread GNSS jamming by both sides. The U.S. military is alarmed.
lustyd
Well-Known Member
That presentation is about GPS and much of it is already implemented in other systems. They’re playing catch up and that presentation reads like a sales pitch for someone to implement the catching up.
No, it does not require updates to receiving hardware. This is a firmware update at most since the primary change is message signing (encryption) to verify known sources (the satellites). It’s not a big change and the Internet has done exactly this for decades. Any spoofing is simply disregarded as it’s unsigned.
No, it does not require updates to receiving hardware. This is a firmware update at most since the primary change is message signing (encryption) to verify known sources (the satellites). It’s not a big change and the Internet has done exactly this for decades. Any spoofing is simply disregarded as it’s unsigned.
Dockhead
Well-Known Member
The planes in the spoofing and jamming map are NOT above hostile territory -- you haven't even looked at it. They are in various places around the world. LORAN is almost impossible to jam -- you would need megawatts of transmitting power. The difference in received power from LORAN and GNSS is something like 10 billion times. That is precisely why LORAN is being revived. And other terrestial technologies are being developed.
Jammers don't need to be on British soil or anyone's soil. The biggest threat is when they are in the air, and there are many cheap and unmanned ways to get them there.
You've apparently decided against all tne facts that disruption of GNSS is a trivial non-issue. Governments around the world disagree, and are spending billions developing or reviving alternative PNT system, including LORAN. Money will spent, in my view.
lustyd
Well-Known Member
You posted a tiny thumbnail showing planes centred around Russian territory in the Baltic, above Russia, and around Ukraine and Iranian conflicts. Whatever you think is there you’re doing a poor job of explaining.
It’s not against the facts, I’ve explained specifically how jamming is overcome in anything but conflict areas as well as how spoofing is a solved problem. You have addressed neither point nor have you explained how Loran would change either one. Just waffle followed by conspiracy theories.
Mark-1
Well-Known Member
Well yeah, but 100w output would need about 300w going in so it would need cooling and a decent power source. For any length of time that really means mains power or a generator. Also needs a good aerial. So it might fit in a backpack but that's not the same as being very portable. It also requires line of sight to all of the victims. ...and the police will be along v. soon after it's switched on.
Yes it could go on an aircraft but if things were so bad that Russia want to circle aircraft over the UK Jamming GNSS they can just as easily smash up the Loran transmitters.
I really can't imagine there are many leisure sailors who are so dependent on an accurate position electronic position that they'd fit an ELoran receiver/antenna for fear of jamming that is technically very possible, but not massively likely. Of course, if mobile phone providers add clever small LF magnetic antennas to phones to recieve ELoran then we'll all have one and the question becomes moot.