19 Apr
2013
19 Apr
'13
9:07 p.m.
On Apr 19, 2013, at 4:00 AM, Dave <dave.g4ugm at gmail.com> wrote:
On 19/04/2013 01:01, Dave McGuire wrote:
That would be a surprise to me, but I suppose it's not impossible. I
know we had a problem a few years back confusing 50 and 75 ohm N
connectors; plug in the wrong one and you'll either potentially damage
the receiving end or get an intermittent, hard-to-diagnose connection
(and, obviously, impedance mismatch problems). Fortunately, we only
had the latter, which is good because the receiving device was a very
expensive network analyzer that we were renting, and we're a small
company. The core problem turned out to be that someone had put both
plugs into the same parts bin, and the tech making the cables was
unaware, and it's damn near impossible to visually distinguish them
without a side-by-side comparison.
- Dave
On 04/18/2013 05:13 PM, David Riley wrote:
All 3270 stuff uses BNC connectors. I don't know offhand which impedance of BNCs
they use (they look like 50-ohm to me) but at those frequencies, a few MHz, the impedance
bump really is minimal.
50ohn and 75Ohm BNC look much the same to me. At one time the pins were different
sizes but you needed a micrometer to tell. I think since 1978 they are the same size...
NO NO NO
NO NO! RG58 is 50ohm, 3270 is 93 Ohm so RG63....
What's the BNC for, then? As far as I knew, they only made
50 and 75-ohm BNC jacks. Or did they just use 75 ohm ones
and hope the brief blip on the TDR didn't do too much to
the signal?