[time-nuts] 50 Ohm vs. 75 Ohm RF cable

lists at lazygranch.com lists at lazygranch.com
Tue Feb 7 23:22:08 UTC 2012

Just a FYI, the "standard" connectors for 75 and 50 ohms are a little different. I will leave it at that, but there is plenty of info on the net regarding the differences. 

------Original Message------
From: Tom Miller
Sender: time-nuts-bounces at febo.com
To: time-nuts at febo.com
ReplyTo: Tom Miller
ReplyTo: Discussion of precise time and frequency measurement
Subject: [time-nuts] 50 Ohm vs. 75 Ohm RF cable
Sent: Feb 7, 2012 3:00 PM

> There is no particular advantage in one or the other, at least not
> for most applications. It's tradition that measurement and (most) RF
> gear uses 50R, while TV and radio uses 75R. (there was once a reason
> for this, but i don't know it).


The reason there are two primary impedance's in use comes from the fact that 
75 ohm cable has the lowest loss characteristics and 38 ohms can carry the 
highest power. For cable systems, they desire the lowest loss for obvious 
reasons. The 50 ohm was chosen as a compromise between low loss and power.

I say this from memory so the exact values may vary a few ohms. The 
information can be found on the net.


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