In article .com,
wrote:

I have a Trompeter PDF tittled "Getting Reday for HDTV". Up unitl the
last few years it was common practice to use 50 Ohm male and female
BNCs in 75 Ohm systems. With a maximum frequency of under 5MHz the
mismatch had ":no" effect. Trompeter arns that older 75 Ohm patch
bays will not pass DTV signals, which can reach up to 1GHz, with
"serious distortion".

I have tried to find a link at Trompoeter, but haven't succeded yet.

These pages shows the difference between 50 and 75 Ohm BNC
connectors. http://sosnick.uchicago.edu/BNC_50_75.html
http://www.levitonvoicedata.com/supp...ote_detail.asp
?tnID=17 5

Almost all of the "older" professional video gear used 50 Ohm BNCs
this

includes Grass VallyD2, BetaCam(BetaCam digital uses real 75 Ohm
BNC), U-matic and Ampex quad and 1".

A local TV station had a major nightmare with their ~20 year old
Trompeter video patch bay. On pass through wouldn't kill the DTV
signal, put a 2nd pass and the video died.

A chief engineer explained that 50 Ohm connectors where "much less
expensive then 75 Ohms" This link gives a 5:1 price differeintial:
http://www.extron.com/technology/arc...tifyingcables1

So in short, if your male BNC has plastic shell on the inside of the
mating fingers it is 50 Ohm, if the female BNC has a plastic collar
around the center pin it is 50 Ohms.

For HF connections I think it is safe to say it will make no
differnce if eith4r 50 or 75 Ohm BNC connector is used. If only
HDTV/DTV were so tolerant, On the good side for us is the fact that
older, but perfectly

good NTSC "75" Ohnm video patch bays will become available on the
surplus market. I was given an older Trompeter 75 Ohm video patch bay
because of the 50 Ohm BNCs. Good deal for me!

Amphenol:http://www.amphenolrf.com/rf_made_si...hquestions.asp
says" At frequencies below 500 Mhz or so, 50 ohm connectors can be
used on 75 ohm cable (and vice versa) with acceptable performance
levels. The reason for doing this is that 50 ohm connectors are
generally less expensive due to their greater usage. Click here to
see a list of useful..."

This thread ought to be interesting......

What are you looking for? Do you want an explanation of why the
connector does not have a big effect on a 100MHz signal and yet has a
great effect on a 1 GHz signal for the same impedance mismatch?

--
Telamon
Ventura, California