[Milsurplus] Why 50 ohm coax?

[mstangelo at comcast.net]

This is the reasoning I have read from multiple sources:

<https://www.microwaves101.com/encyclopedias/why-fifty-ohms>

77 ohms provided the lowest loss while 30 ohms handled the most power. An impedance around 50 ohms provided a compromise.

Mike N2MS
 
> On 10/14/2024 1:00 PM EDT Al Klase <ark at ar88.net> wrote:
> 
> 
> 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.