[octoberfranklin]

The M-code is transmitted in the same L1 and L2 frequencies already in use

Nothing says that they have to transmit M-codes from the spot beam antenna.

In fact, since the M-codes are hardly used, it's pretty certain they're using that antenna for something else. How very convenient that those antennae are designed to transmit on the same frequency as the "ordinary" antenna.

[T-A]

Today I took the time to have a closer look. Turns out, the directional antenna for M-code is only present on Block III GPS satellites, and only four of those are currently in service:

https://en.wikipedia.org/wiki/GPS_Block_III

So this is definitely not the correct explanation.

Besides, even if there were enough Block III satellites in orbit to provide constant cover of the affected area, it would still make little sense to tie up their most advanced capabilities to jam their own legacy signal, when you could just turn off the legacy signal when transiting the target area and provide your own military with continued service using the directional antenna.

And of course, Russia has its own satellite navigation system

https://en.wikipedia.org/wiki/GLONASS

so you'd also have to explain what the US and NATO could hope to gain from turning off GPS.

[T-A]

> The M-code is transmitted in the same L1 and L2 frequencies already in use

Let's quote the whole thing, shall we?

The M-code is transmitted in the same L1 and L2 frequencies already in use by the previous military code, the P(Y) code. The new signal is shaped to place most of its energy at the edges (away from the existing P(Y) and C/A carriers).