Wireless : Can I extend the antenna on a DX210/410/300/100/121 by 40m (120ft)

Using LMR-400 and or LMR-600 for a 40 m (120 feet) remote antenna run would sufficiently reduce the effective RF energy at the remote antenna. 

Here are the numbers: LMR-400 ultra flex:

30 ft at 2.4 GHz = 2.7 db loss (57.8% radiated power at the remote antenna run)

50 ft at 2.4 GHz = 4.5 db loss (40.1% radiated power at the remote antenna run, this would be my pain threshold)

120 ft at 2.4 GHz = 8.0 db loss (16% radiated power at the remote antenna run, pretty much no RF available at the remote antenna run)

Here are the numbers: LMR-600:

30 ft at 2.4 GHz = 1.5 db loss (74.2% radiated power at the remote antenna run)

50 ft at 2.4 GHz = 2.5 db loss (60.8% radiated power at the remote antenna run)

120 ft at 2.4 GHz = 5.1 db loss (30% radiated power at the remote antenna run, pretty much useless for remote antennas at this length)

Some other things to think about: LMR-400 ultra flex coaxial cable is fairly flexible, but it can still be tough to work with especially if your remote antenna run is a temporary installation.  The cable diameter is .405 inches and it uses a stranded center conductor which lends itself better to repeated bending and temporary installations. 

LMR-600 low loss cable is going to be a real bear to work with. The cable diameter is approximately .590 with a solid center conductor so making this work with a temporary installation would be difficult.  LMR-600 is really best suited for permanent installations.  Also remember that the reverse TNC connectors at each end also add a minute amount of RF loss.   See this information from Show Me cables, they can make custom cable lengths for LMR-400, didn’t see anything for LMR-600.  Link to their website:  http://www.showmecables.com/ As with most wireless IC users contemplating the use of remote antennas via coaxial cable, it is far easier to run audio cable than it is to run RF coaxial cable, especially at 2.4 GHz where the loss adds up very quickly.

Note: The cable calculations were referenced from the Times Microwave online calculator.  https://www.timesmicrowave.com/calculator/