Ohiohmmwv,
When the HMMWV was first introduced the most commonly seen radios were the VRC-12 family of radios. These consisted of various mixes of the following radio sets. Some of these numbers represent combinations of the basic sets and nomenclature can be totally confusing to the beginner.
VRC-12 non-encrypted VHF radios:
Transceivers:
PRC-25 or PRC-77 Low power VHF manpacks adapted for vehicular use by installation using the AM-2060, then knows as VRC-53 or VRC-64.
RT-246 or RT-524 High power VHF sets mounted in the M1029 shockmount then known as VRC-43 thru VRC-49
Receiver:
R-442 VHF receiver sometimes referred to as a guard receiver
After this series of radios the SINCGARS radios were introduced around the time of the Gulf War in the early '90s.
Transceivers were the RT-1439 and RT-1523(v)
The difference being the 2 is the RT-1523 had embedded crypto.
The RT-1523 when placed into vehicle adapter AM-7239(v) and then installed into the MT-6352 became sets VRC-87 thru 92.
The RT-1439 got put into an AM-1739 and then that was installed into an MT-6576.
Here's a link to Brooke Clarkes very informative page on Sincgars:
http://www.prc68.com/I/RT1439.shtml#MT-6352
There are hundreds of different configurations used in the HMMWV depending on the unit mission. Probably the most common current radios are those made by Thales and Harris.
Hope this helps answer your question.
Kurt
KG6KMJ