Radio guts, hardware cryptography modules, power amplifiers, and batteries. They've shrunk over time but still aren't small. When I first joined the Marine Corps, we had ground radios for each of the major spectrums: HF, VHF, and UHF (LOS and SATCOM). Now, most of the radios are multi-spectrum (combined): HF/VHF and VHF/UHF/L.
The AN/PRC-117G is an example manpack radio used by the Marine Corps today. We use it for voice and data.
If you're not familiar with radio wave propagation, don't get suckered into thinking hand-held radios can always replace manpack radios or that manpack radios can always replace vehicle radios. The art of radio involves a balance between power, proper antenna use, and terrain. Small, hand-held radios often don't have enough power to transmit a signal the distance you may need it to go in whatever terrain the person is in.
I still don't get it. I mean - when you're talking about power supplies, there are welding power supplies that are light. A power supply is lighter by default these days because they can be made with mosfets instead of big, heavy transformers.
As for hardware cryptography modules - again - you can buy an ARM chip that's the size of your thumbnail that's basically a full blown computer.
I'd be interested to look at the insides of one. I wouldn't be surprised if making them EMP hardened would be a big component of where the bulk comes from.
Switch mode power supplies are small, but the batteries to power them are not.
NSA certified crypto modules aren't in an ARM chip the size of your thumbnail.
The AN/PRC-117G is an example manpack radio used by the Marine Corps today. We use it for voice and data.
https://www.harris.com/solution/harris-falcon-iii-anprc-117g...
If you're not familiar with radio wave propagation, don't get suckered into thinking hand-held radios can always replace manpack radios or that manpack radios can always replace vehicle radios. The art of radio involves a balance between power, proper antenna use, and terrain. Small, hand-held radios often don't have enough power to transmit a signal the distance you may need it to go in whatever terrain the person is in.