Stereo Tool

Is there a way to use Micro MPX Decoder when the WAN address is unknown such as with a cellular 4G data connection?

Yes.
Use a VPN tunnel. Your VPN server can have a public IP address. Ideally, the VPN server is at your studios, and the µMPX Decoder at the transmitter just connects to your VPN whatever connection it finds, be it 4G or copper ...

Thanks. Now need to read up or find someone who knows how to build a Vpn tunnel!

If your studio has a fixed IP address, I'd recommend WireGuard. Very lightweight and little to non bandwidth overhead.
If your studio has a dialup-style connection with changing IP address and dynamic dns hostname, I'd recommend OpenVPN.
Reason: Wireguard doesn't (yet) support changing IP addresses. You can write your own scripts to solve this, but that's certainly advanced use.

So read some WireGuard or OpenVPN tutorial, where you studio is the "server" site, and your transmitter is the "road warrior". Then with a bit of routing magic (allow road warrior to access all devices on your server sites subnet) you'll be able to talk to the transmitter site decoder using it's VPN client IP.

Thanks for your reply, sorry for my mega slow response.

Stupid question time, will Wireguard make my remote transmitter site look like it's actually on my studio LAN where the Wireguard server will be? Eg instead of typing a WAN IP in uMPX encoder, I'll be entering a LAN IP?

It looks a little complex with the command line, but if I can picture what I'm trying to achieve, I stand a chance of getting it configured right!

Yes and no.

Your transmitter will get an IP address from a private address rage dedicated to the VPN/Wireguard tunnel, 192.168.x.y or the like. And you would enter this internal IP into your studio µMPX encoder.

Meanwhile, I have set up studio transmitter links using Tailscale. For up to 20 devices it is free and it does all the magic for you, including finding ways to get a connection where other methods would fail, like having both ends of the connection without public IP addresses.

It uses wireguard under the hood and makes best effort to establish a peer to peer connection, where this fails it uses a bounce server to transport packets. The first is preferred of course. On top, Tailscale offers a clever ACL so it is perfectly possible to set up your machines to only exactly move the µMPX data stream from studio to transmitter, not the other way round nor anything else.

I'm not affiliated with Tailscale, it just does exactly what we needed for our stations here, with ACL and routing magic being the outstanding features that would be difficult to implement on your own. And so far it is rock solid and copes with power fails and internet connection issues very well.