So I am using rg 62 coax which is 92 ohm. My BNC connectors are 75ohm.all my equipment inputs and outputs are 92ohm. Do I need to use 92ohm terminators on all my T's and where,at the source or load? Thanks jf
If your frequency is below, say, 1 GHz, the connector impedances won't matter, as long as they mate mechanically.
One usually tee-terminates a coax at the load end. If your frequency is low compared to the cable length, you probably don't need to terminate at all.
What kind of equipment is 92 ohms?
-- John Larkin Highland Technology, Inc lunatic fringe electronics
Some missile/radar systems use 90ohm internally. Really sucks trying to use regular 50 ohm equipment to troubleshoot.
I thought that BNC was only good to 400MHz or so, and that you wanted TNC above that.
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..... Phil
OK, so I was off by 10dB -- I got the significant figure correct.
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Old car radios, early IBM computer terminals.
RG62 is 93 Ohms.
-- Never piss off an Engineer! They don't get mad. They don't get even. They go for over unity! ;-)
With decent quality cables and connectors, BNCs are good to 3 GHz or so. TNC is rare these days; most people go to SMA at higher frequencies. Some RF test gear still uses type N, and if we have that we scrunch on an SMA or BNC adapter.
We use a lot of SMBs on our boxes, because they are easy to mate/unmate (SMAs are a pain) and they can be spaced close. SMBs are good to at least 10 GHz.
-- John Larkin Highland Technology, Inc lunatic fringe electronics
I know little about HF RF. But I would think a mis-matched connector is not going to cause all that much of a problem. I'd certainly add termination resistors at the receive end. And maybe a series resistor from a 50 ohm signal generator at the source end.
Or throw-away signal at the source end and make a resistor Tee that look like 50 ohms in and 92 ohms out... (Hey is that possible?)
George H.
I'm using nim electronics,the pulses from my photomultiplier are about 10 NSA.
That's nanosecond not NSA, I'm using a Ortec pulser .
Much depends on how good you need it to be. I did some TDR measurements on various connectors, or between-series adapters really, but that gave a good view of the relative merits of SMA, N, BNC, SMC and LEMO-00 50 Ohm connectors.
See .
Sorry, no TNC in there.
Jeroen Belleman
Good grief, that LEMO terminator is awful.
A lot of cheap terminators have an ordinary axial thick-film (spiral element!) resistor inside.
Surface-mount resistors are usually pretty good.
Here is a mess of SMBs, both TDR and TDT.
The output is pretty clean, 37 ps risetime, which is almost 10 GHz.
Some BNCs:
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
50 or 75 ohm BNC connectors will be fine at 10 ns. But the comment "use 92ohm terminators on all my T's" is sort of scary. Can you post a sketch of the proposed setup?
CAMAC is dead, but I guess that NIM is still around.
-- John Larkin Highland Technology, Inc lunatic fringe electronics
I started my career debugging CAMAC and NIM modules. Somewhat later also FastBus and VME. CAMAC and FastBus are all but dead, but we still have a lot of NIM bins. Simple is better, I suppose.
Jeroen Belleman
I did a lot of CAMAC too, modules and even crates and crate controllers. It was sort of a goofy bus, designed by physicists. The good parts were the geographic board select and interrupt lines.
VME is still alive. It has survived the many other busses that were supposed to kill it off.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Old, usually. A 7400 gate can sink 16 mA. To drive a 93 ohm load with 3.5V, you need 38 mA.
So there were 'bus driver' gates made, SN7438, with open collector output and 48 mA drive.
A few decades back it made good sense to run 93 ohm cable, because that meant you could use mass-produced drivers and regular ol' TTL for receivers.
He's terminating his cable with a bnc Tee and resistor. I've done that with ~20' of cable from a PMT to some crate. (50 ohm cable) We'd put Tee's on both ends, 1/2 the signal, but less bounce on big pulses.
George H.
Good work, boy. Hope the pay you well.
w.
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