Use the Security Base Frequency
Tune your spotting scope to 71.2 for the PACE security base, then check that locking onto the signal updates your main quest. Use the scope's additional frequency-adjustment controls while looking through it.
Follow the Journal's Settlement Lead
Your journal points toward a settlement for the frequency search. A log lists several frequencies, including 71.2. That is the useful setting to take into the spotting scope for the security-base objective.
If you want to follow the clue yourself, use the journal's settlement lead to guide your search. If you mainly want to continue the quest, try the frequency directly: manually tuning to the successful signal also advanced the main quest.
Tune the Spotting Scope and Check Progress
- Open the journal with J to bring up your quests and review the current objective.
- Look through the spotting scope to access the additional buttons or keys used for frequency adjustment.
- Adjust the frequency to 71.2, looking for the clear warning or sign that identifies the desired signal.
- Check your main quest after locking onto the signal; the successful frequency detection should update it.
- Select the saved preset when you need the frequency again; discovering the channel should make it available for later use.
Check the Signal Before Searching Elsewhere
If you have been trying 52.8, switch to 71.2 for this objective. The former is the PACE Antenna frequency. The security-base answer is the setting that produced the main-quest update.
If changing frequencies seems to do nothing, check that you are looking through the spotting scope and using its additional adjustment controls. Watch for the clear warning or sign as you tune. Then check the quest rather than judging success from the displayed number alone.