Use radios: Gmrs or Ham

Do not transmit from your base, travel somewhere further away, then broadcast. Change location of broadcast every time.

Use encryption.

One method is using my Rattlegram + SSE method (both open source)

Rattlegram is a mobile app that converts text into audio

You play this audio over the radio, and the other side can use this to decode and get back the text.

All you have to do is encrypt the text using any open source program. I like to use SSE (Secure Space Encryptor / aka: Paranoia Text Encryption on iOS). You could also use PGP, but it would take longer to transmit the message since asymmetric encryption results in longer ciphertext.

Copy-paste the ciphertext into Rattlegram and voila! (Just reverse the process on the other side to get the plain text)

Obviously you shouldn’t use any iOS or Googled Android. Use Graphene OS or something like that. Physically disable the antennas on the phones, you need them airgapped.

Alternatively, you can use One Time Pads, although it would be slightly harder to generate, distribute, and store OTPs, but if you use OTP, you wouldn’t need to rely on digital encryption, and its more secure, but it’d be much slower to manually encrypt your text.

For resistance radio stations: Shortwave - although there aren’t really any interesting stations right now, but if a civil war starts, I could see someone in Canada or Mexico start broadcasting to give the US revolutionaries info. Shorwaves can travel long distances.