I build my -powered- defense relay very close to the archaeological site, as close as I can get them and I still cant complete the mission.

https://www.youtube.com/watch?v=C--0Z-y2rnA
In this youtube video, at the end, you will see where he builds the relay, I have built mine in exactly the same place. I have built them all around the mountain and still cannot get the defense relay to cover the archaeological site completely...

Did this last night, so I can assure you it works. Important question though - does it link all the way back to your field back at base? i.e. - can you trace a path back to your matter converter? You'll know if you can't, you get a yellow icon when you try to place new relays.

Once it's all one unified field, you'll get the win. :)

You can build a Converter near the site aswell and build a def relay next to it. Finish.

go underground relay works for both surface and under ground

Thanks for the replies. I did have my relay connected all the way back to the converter and a green shield indication, indicating that my relays were indeed powered.

After reading these replies I tried again, and the mission completed. I am not sure what the issue was but it just completed as I was building a second matter converter near my relays. It wasnt even completed. Anyways, thanks guys.

Now I play MF campaign, and I replayed 2nd Rimtech mission several times. The pesting Neuropa raids gave me troubles every time. Only yesterday I won it quite easily.

I just built 3 ComBots, swept away the annoying Neuropa base just south-west of my own base, so the whole northern half of the map was mine, and then built a chain of DefRelays up to archaeological site to the west.

It seems that alternative ways exist (like using underground level, with one elevator right beside your base and other not far from archaelogical site) but I used underground only for lava mining when my initial lava pool ran dry.

Mark though that in such way I didn't get the maximum upgrade points for this mission; I just got 16 for the main objective completed, and there are 5 more for destroying all enemy units. So I assume there's some more Neuropa forces in the southern part of the surface map, and maybe some more underground.