Re: Signal Generator Source Impedance

On Mon, 29 Apr 2024 18:26:11 +0100, Cursitor Doom <cd@notformail.com>
wrote:

On Sun, 28 Apr 2024 11:06:55 -0700, Jeff Liebermann <jeffl@cruzio.com>
wrote:

(chomp)

A much bigger problem is that 50 and 75 ohm BNC connectors use
different center pin sizes. 
<https://www.vintage-radio.net/forum/attachment.php?attachmentid=30120&d=1258015846>
I wrecked the 75 ohm receptacle on a CATV sweep generator by force
fitting a 50 ohm BNC plug.  Color coding my cables have largely
prevent a recurrence.  Green tape or nail polish for 50 ohms and
violet for 75 ohms.

>
Aha. Saw what you did there, Jeff: resistor colour code; green = 5 But
Violet Gives Willingly. ;-)

I thought about it and decided I didn't need to color code the cables
beyond the green (5) and violet (7).  For 50 ohms, a second stripe
would have been black (0), which is invisible when applied to coax
cable with a black outer jacket.  For 75 ohms, the use of a green
second stripe to would guarantee confusion with the 50 ohm cables.  I
decided that a 2nd color coded stripe was a bad idea.

Mostly, I use vinyl electrical tape, but had some difficulties
obtaining violet tape.  Shrink tube was better, but more difficult to
attach with different diameter coax cables.  I finally settled on
embalming the tape with transparent packing tape, which also allowed
me to attach text to the cable. 

I also have small round sticky dots in green or violet for identifying
the impedance of the BNC receptacles.  Noticing a color mismatch
before inserting the BNC plug has prevented a few disasters when I'm
working late and half asleep.


--
Jeff Liebermann                 jeffl@cruzio.com
PO Box 272      http://www.LearnByDestroying.com
Ben Lomond CA 95005-0272
Skype: JeffLiebermann      AE6KS    831-336-2558