[Milsurplus] Why 50 ohm coax?

[Al Klase]

Nick,

Interesting.  75 ohms is really close to a dipole in free space.  I had 
wondered about that.

Thanks,
AL


On 10/14/2024 12:15 PM, Nick England wrote:
> From a Trompeter tech paper - something I never heard before
> -----------
> The most efficient Impedance to use
> when transmitting any signal considering the voltages, cur·
> rents and powers to be transmitted is 75 ohm, and would be
> the only standard if these were the sole considerations. The
> telephone industry, followed by the TV Industry, use 75 ohm
> almost exclusively for the transmission of video, baseband
> and I. F. frequencies. The military services during the period
> 1920 through 1940, were faced with a differing need for low
> radiation angle omnidirectional antennas for broadcasting
> ship to ship, airport tower to low flying aircraft and base
> station to ground troops. The only antenna that would give
> this performance was the vertical ground plane In Its many
> forms, which turned out to be 50 ohm . The military standard·
> ized on 50 ohm impedance and spent vast sums of money
> developing cables and connectors for all of their coax
> systems. At one time a military agency, Armed Services
> Electro Standard Agency (ASESA) designed all military
> coax components and assigned the connector UG and
> cable RG designations. This has since been replaced with
> the latest government/Industry committees cooperating
> and producing the current general connector standard MIL·
> C-39012 primarily for 50 ohm usage.
> ------------------
> Nick England K4NYW
> www.navy-radio.com <http://www.navy-radio.com>
>
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-- 
ARK Sig Block Al Klase - N3FRQ
Jersey City, NJ
http://www.skywaves.ar88.net/
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