During the Horizon Forbidden West Signal Spike quest you need to track down the source for a signal, at the request of a character named Silga. By using metal 'spikes' as antennas to get an old world radio transmitter working, she's accidentally started picking up sections of an ancient distress signal being broadcast from a mystery location, so you need to work out where it's coming from. This shouldn't be a tricky task in Horizon Forbidden West, however there are some unclear signposting and objectives to deal with that can make things feel confusing as you work towards the conclusion. So, if you're not sure what you're looking for then we're here to clear things up, by explaining how you find the source of the signal in Horizon Forbidden West Signal Spike.
How to find the source of the signal in Horizon Forbidden West Signal Spike
Most of the Signal Spike mission is fairly simple: when you meet a tinkerer called Silga, you'll discover she's tracking ancient radio broadcasts using 'spikes' in the desert (basically old aerials). Initially you help her by climbing to the spike near her and using your Focus to scan the signal. Once that's done the rest of the mission will see you travelling to different locations to find a spike and scan the signal. That will eventually give you everything you need to locate the source and access the final part of the mission, where things get tricky.
When you get to the Source of the Signal quest you'll find Focus scanning doesn't really help any more. The source is a canyon full of machines you need to clear out, and once that's done there's no broadcast to find, only a purple signal behind some rocks you can't move. Aloy will say you're not getting in that way and then just leave you to it.
It's easy to get stuck here because the whole mission has been about finding and listening to radio signals with your Focus high up. A ground level purple blob behind a wall you can't interact with doesn't match anything you've done, so it's not surprising if you have no idea what to do next.
To actually find the source of the signal in the Horizon Forbidden West Signal Spike quest you need to climb up to the top of the middle bit of the canyon and look to the ground below you to the north, with your focus:
You should see a white diamond that Aloy will say looks promising. This easy to miss wall, nowhere near the signal, is the one you can pry open to reach it. It's here if you're having trouble (it's almost impossible to see at night).
Once inside you'll find water you can swim through to reach a buried plane and inside is the transmitter that's been broadcasting the signal. Once you've finished (don't forget to grab the supplies in there too) you can escape by prying open the first rock wall you couldn't do anything with before...
Then, just head back to Silga to complete the mission. You'll get to keep the Military Equipment you salvaged which can be used to make the Spinthorn Spike Thrower - a spear weapon that does damage over time and rips of machine parts as it's doing it.
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