I can only guess the limitations of technology made two way radios very expensive and larger than receive only. It might also have been cultural with respect to exposure to technology?
Two way radios were not only more expensive and larger. They also required more expertise to operate them correctly.
Think back to early car radios (for those who are old enough). You used to "tune-in" to a station by turning a dial. You learned that the clarity of the station you were tuned to changed with the terrain, and with the power of other stations nearby in the frequency spectrum, so you often tweaked the dial a little to improve the reception.
We forget about these things with modern radios that have digital tuning, where the radio does the tweaking for us.
Now, if you have a receiver, and the broadcast comes in better at 91.4khz than the specified 91.3khz, due to some climatic or terrain, well that's no big deal. You just tune the dial a little bit one way and the other until it sounds better.
But if you are the broadcaster … you are expected to be ON frequency. And if your unit is wandering off frequency because of moisture in the air, or the magnetic field of the 40 ton metal box it is being carried in, or the heat of that metal box in the sun, or because it has been bounced around too much by driving that metal box and firing off the cannon in that metal box … well, when you wander off frequency the people that you want to hear you probably can't hear you! And they might not know that they can't hear you, because they don't hear you saying "can you hear me?", and you don't know that because, well, they didn't answer because they didn't hear you (or because they are receive-only).
It is all easier when you are only receiving. Because it is easier to correct if you are off, if you are the variable and the target (the broadcast) is fixed. Once the target (the broadcast) starts varying, it becomes a multi-variable problem that is many times more difficult to solve.
In my readings it seems to me that the need for simplicity led the Soviets to focus on fixed-frequency crystals (no tuning) in the design of their radios. A receive-only radio was manufactured with a single crystal, and received only 1 frequency. It had on/off/volume control only. Nothing else to fidget with.
In those cases where they had multi-frequency capabilities (ie: company and battalion commanders) it was in radios with two or three single-frequency crystals. So you could choose channel A or B or C, but you could not "tune" to find the best signal strength. This was one reason that Soviet radios were less effective in the field (along with poor quality control in the manufacture of the crystals and the assembly of the radios).
And blah blah yadda yadda.
The key is that voice radios were fiddly bits of equipment in 1940, and specialized training was needed to operate them effectively. Almost all tanks that carried radios at the start of the war carried their radios in the hull, next to that guy we now call the bow-gunner, who was usually a trained radio operator. His main job was to keep the radio operating correctly, and his secondary job was to help the driver. Firing a bow MG was more of an after-thought. And actually it WAS an afterthought, as some very well known AFVs had the guy, but not the gun (like the French S35, or the US M10, M18 and M36 TDs and M8 armored car).
At least that's what I've come to understand.
-Mark
(aka: Mk 1)
