It’s important not to confuse coaxial cables made to current Military Specifications (M17/75 or Mil Spec) with those now simply labeled as “RG”. In order to regulate and develop specifications for coaxial cable used during WWII the Government adopted a series of cable designations taken from the Radio Guide and know as “RG” to define coaxial cable type, size and construction. Unlike current Mil Spec coax which must meet tough specific criteria, RG coax made today meets only the standards of the company producing it. While all RG cables of a certain name may be the same size, RG does not define construction standards of even materials in many cases. In the Ham and Amateur Radio world RG continues to be used mainly to define cable size and type due to the years it was an accepted standard. These types of coax cable were once all listed in the MIL-HDBK-216 which is now obsolete and has been replaced in military use by newer design specs.
Almost all analog and digital audio and video antenna feeds use 75 ohm coax cable while WIFI, CB, and Amateur Radio (HAM) are designed to transmit and receive using 50 ohm cable. With hundreds of different coaxial cable designs and sizes, selecting the proper one for your application can be tough. Considering the capability requirements of the cable you use, the next big decision is what amount of loss you can accept in broadcasting to your antenna. In certain applications a lower quality RG coax at a cheap price may be all that is required to operate but in most cases Ham and CB operators will want the best transmission line available. This is normally not the older style RG coax variety. In today’s climate, coaxial cable design and quality requirements standards for RG cable types can be totally defined by the maker in terms of transmission loss, rated VSWR, power handling and other requirements. One brand of RG cable will vary from another, there is NO RG Standard that applies to loss, quality, power rating or construction quality of coaxial cable. RG, today simply tells us the style and dimension of coax cables. The “RG” designation used to have meaning in defining a cable standard at one point in time but that is no longer the case.
In the newer Times Microwave system for naming cable actual coax cable diameters are used. Times Micro makes LMR400 at.4 inches and LMR-195 at point.195 inches making them the same size as the old RG-8 and RG-58 coax standards but with a different construction standard suitable for microwave transmissions. Makers of newer style ultra low loss coax like Times Microwave use a different naming system to update the RG standard to something that makes sense. The RG number of the coax cable has nothing to do with it`s size or type relative any other cable, RG-400 is tiny and RG-8 is almost half an inch thick. RG coaxial cable naming conventions are so confusing you just know it was a system designed by the government. Ultra Low Loss coaxial cable like Times Microwave LMR-400 is great quality coaxial cable made to the higher Mil Spec standards and is much thicker than common types like RG-58, but it also costs more. Times Microwave, the originator of LMR cables, is a technology leader in coaxial cable design and development and it’s LMR-400 and 240 cables set the standard for quality. As the leader in coaxial cable technology, Times Microwave developed LMR-400 and 240 to create the best cable possible for use in Ham and Wifi. In order to attain the low loss offered by standard hard corrugated coax cables but get the flexibility needed from average Ham and CB installs Times Microwave produces LMR400 and LMR240 type cable.