Why is 50 ohms the industry standard for all modern two way radios?
Why is 50 ohms the industry standard for all modern two way radios?
Prior to Word War Two there was no standard output impedance for two way radios.
Early radios used tubes which had a high input and output impedance. The output tube or Final was adjusted each time the operator changed frequency. By "Loading" the plate and the grid using variable coils and capacitors, the output tube could be matched to the antenna, insuring a maximum transfer of energy. When the transmitter output impedance is the same as the antenna input impedance you have a 1 to 1 SWR or "Standing Wave Ratio"
Due to war time rationing it was determined that an impedance of 52 ohms used the minimum amount of materials to make coaxial cable. Copper and other metals where used for the war effort. During that time no cars were made and everything was recycled, even pennies were made of steel in 1943.
Nickels made between 1942 and 1945 use 35% silver instead of nickel. After the war the standard was kept at 52 ohms and eventually was rounded down to 50 ohms. This is still the standard used today.
With the development of transistors in 1948 the output impedance was fixed to 50 ohms, which worked out well because the output impedance is low unlike the vacuum tube.
Author Rick Lewis - The CB Doctor
Visit Rick's website at TheCBdoctor.com
Tags: CB Radio Antenna