Faelwolf

I am an old USAF telecommunications specialist (80-84), so let me see if I can explain without writing a book, or screwing it up too badly with my lousy writing skills

The problem was mainly a technical one. In WW2 and even up through the mid 60's, field radios were single crystal sets to reduce size and weight. Considering WW2 was before transistors, size and weight were relative terms. Vehicle radios could be larger and had more power available, so could be multiple crystal sets and have a wider frequency range. There were communication jeeps that had a radio setup that looked like something out a 30's science fiction serial

Larger HQ units also had the multi crystal sets, and multiple radios, but a Coy commander was not as likely to be as well equipped. The Coy HQ support unit would have been equipped with radios for command and control, not relaying mortar requests. Even if they had radios with the right frequency, they would not likely be tuned to those channels. Communication protocols were in place that kept radio communication into separate nets so they would not be monitoring that net, and would be too busy monitoring/relaying C&C traffic to switch over anyway. HQ was also not likely to be in position or have the inclination to sit and relay mortar requests either.

The radios were issued in frequency sets, with different units receiving different sets to keep communication separated to prevent confusion and reduce enemy infiltration of the comm net (in theory anyway). We discovered the hard way that it also prevented inter-unit communication as well. Remember that back then radios were a fairly new item for the military, and the protocols were developed in peacetime when it was easy to overlook potential issues.

So, if the crystal in your radio did not match the crystal of the radio back at the mortar section, or there was not a multi crystal/radio setup near them, they would never hear you. Due to protocols, someone with the right radio wouldn't be tuned to you and wouldn't hear you. I will skip the other problems like terrain issues, enemy jamming, equipment breakdowns etc. that could interrupt comms, especially since they aren't modeled in the game. If anything, the game makes radio communication to the mortars too easy, though given the lack of runners, field telephones and carrier pigeons I think it's a decent compromise If the game was thoroughly realistic on radio communications, it would be a major pain to do any comms. I just accepted the limitation with HQ support as a nod to realism, and was glad they didn't take it further.

This is just from the U.S. point of view, radios were much more limited in the other services, so it would be worse if you were playing on those sides.

These days it's all digital, you can switch comms with the twist of a dial, and we rely on digital encryption to protect the net. I also wouldn't be surprised to find troops texting info to each other on their cell phones! But it makes it easy for us to forget what it was like to have a single crystal tube radio with a HAF battery strapped to your back, calling for support and hoping the slob back in the rear could hear you.

Having just gone through this exact thing within the past hour, I can give a couple tips, and my experience.  I can't complain too much, my old drive had 13.5K+ hours on it, and was still limping along as best it could, but it was time to replace.
I downloaded the 3.0 patch, which gave me the 9GB file.  Once it downloaded, I did the install, which put a bunch of icons on my desktop.  One of them is for the activator.  I have my keys in a .txt file I created, which made the process a lot easier.  If you don't have something similar, you can copy and paste from your account on battlefield.com, so they are not lost.
 
Goofy thing with the activator to be aware of, at least it's what happened to me.  It will ask for the serial # of the CMBN game, which looks like it is asking for the original serial #.  It is not, it wants the serial for the 3.0 update.  This will give you the base game, updated to 3.11.  Don't launch yet, if you own the other modules, you need to close the activator, and re-open it again to be able to add another serial.  Do this for each module you own, then launch once they are all in. 
 
It won't hurt if you launch early, but you won't have access to the other modules until you run the activator again, so best to just knock it out.  Also, I had an odd graphics thing where it didn't tell me what modules are active, it's like there is a header, but the info doesn't get put in underneath it.  Not a big deal, as there aren't that many modules to track, but it could use a fix, along with the lack of an ability to active more than one module at a time.
 
So in summary the interface is a bit goofy and confusing, but it sure beats the old system of having to figure out installation order and hope you didn't foul it up!  I would also prefer not to have so many icons on my desktop to have to clean up when I am done, but that's also not a major problem, just an annoyance.
 
Edit to add: Nice K-Bar is it a genuine Camillus?