Why 50 ohms output impedance?

[TheCBDoctor]

Interesting enough prior to WWII different radio manufactures used different output impedances for two way radios. What standardized the output impedance to 50 ohms was a question of resources during a war that rationed everything.

Copper was in great demand for munitions. It was decided that not only was a standard required, so that any company can make radios and antennas, but that 52 ohms was the coax that would use the least amount of copper and other materials.

After the war the impedance became 50 ohms. I am guessing it was just to round down to an even number. I don’t see much of it any more, but I have run across 52 ohm coax. I never bother to check if it is still made today, but I doubt it. The 52 ohm coax that I had was probably lying around in some old-timer’s basement.

Tubes have high output impedance, which had to be reduced to 52 ohms. The transistor was developed in 1948 and had low output impedance, which worked out in the end because it was easier to match the antenna impedance of 50 ohms.

If you are using 52 ohm coax or 50 ohm coax I would not worry about it since the difference is so insignificant that it doesn’t affect your SWR, but the law of physics dictates that you will have a maximum transfer of energy when the impedances match.

Just a bit of info in case anyone really cared.

Respectfully,

Rick

[Deleted User 14541]

Interesting. Thanks for sharing.

[KP68]

Interesting enough prior to WWII different radio manufactures used different output impedances for two way radios. What standardized the output impedance to 50 ohms was a question of resources during a war that rationed everything.

Copper was in great demand for munitions. It was decided that not only was a standard required, so that any company can make radios and antennas, but that 52 ohms was the coax that would use the least amount of copper and other materials.

After the war the impedance became 50 ohms. I am guessing it was just to round down to an even number. I don’t see much of it any more, but I have run across 52 ohm coax. I never bother to check if it is still made today, but I doubt it. The 52 ohm coax that I had was probably lying around in some old-timer’s basement.

Tubes have high output impedance, which had to be reduced to 52 ohms. The transistor was developed in 1948 and had low output impedance, which worked out in the end because it was easier to match the antenna impedance of 50 ohms.

If you are using 52 ohm coax or 50 ohm coax I would not worry about it since the difference is so insignificant that it doesn’t affect your SWR, but the law of physics dictates that you will have a maximum transfer of energy when the impedances match.

Just a bit of info in case anyone really cared.

Respectfully,

Rick

Really care? HECK YA! I absolutely love everything about radio history. I always knew it was an agreed upon standard, but I never knew the origin. Thanks Rick, Love it!!

[grease rag]

Very interesting. Thanks for sharing

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