So I am thinking

1: 3-output signal source each output centered on each of the Glonass bands.

2. Probably some FM sweep of each band +/- a few hundred kHz.

3. A 20W amplifier on each output (let's see what devices we can find that aren't hit by the semiconductor shortage. I used some cheap ones for GSM a while back). Each amp could have a circulator to minimise reverse signals which lead to intermodulation.

4. 3 Separate antennas spaced a few m apart, to minimise coupling and therefore intermodulation. We don't want emissions to overlap GPS or Galileo. Alternaticely a power combiner if we can keep the isolation high enough.

5. Power supply - mains 60W - make it quite flexible say 12V up to 19V DC so you can use old laptop supplies and/or a car battery.

6. A reverse polarity diode just in case, with a warning LED, to make it idiot-proof.