BNC adapters...

[alank2]

Hi Everyone,

I'm looking to get a toolkit of a few pass through BNC adapters I've seen mentioned here in threads.  A 50 ohm terminator, some attenuators, etc.  Where is a good place that has these at a reasonable price/value/quality level?

Thanks,

Alan

[alm]

I would not call an attenuator or terminator an adapter. Mini-circuits have some reasonably priced attenuators. Feed-through terminators from the usual suspects like Pomona are expensive, I haven't found a cheap source yet. They occasionally turn up used on eBay. Not a whole lot that can go wrong unless someone overloaded it. Used Tek feed-through terminators (not the precision or 3W type) have better specs than new Pomona feed-through terminators (lower VSWR).

[alank2]

alm you are totally right, they aren't adapters!

[Sigmoid]

On Mouser you can get 1W 50ohm terminators for peanuts ($2), I'm thinking of getting a bunch. According to spec they are good to 4Ghz. I don't think that I'd normally want to drive a function generator above 7VRMS, so I guess 1W should be kind of enough.
A tee costs maybe $4, so you have a feed-through terminator under $10.

[alm]

The performance of a tee + standard terminator is inferior to a real feed-through terminator, though. The terminator should be as close as possible to the input. Not necessarily a problem for relatively low frequency work, but I wouldn't use it for fast signals. There's a reason why real feed-through terminators are sold and bought.

[Sigmoid]

The performance of a tee + standard terminator is inferior to a real feed-through terminator, though. The terminator should be as close as possible to the input. Not necessarily a problem for relatively low frequency work, but I wouldn't use it for fast signals. There's a reason why real feed-through terminators are sold and bought.

Where would you put the frequency threshold when the difference starts to become noticeable?

[alm]

I would start worrying above 100 MHz or so. The Pomona feed-through adapter is specified up to 500 MHz, and the Tek one to 1 GHz. Note that a scope will still display signals somewhat beyond its bandwidth. A 100 MHz scope is -3 dB down at 100 MHz (30% attenuation), but may attenuate 200 MHz signals for example by 65%, so an additional attenuation of 200 MHz signals may still be noticeable.

One signal where I would expect it to make a difference is in the Jim Williams pulse generator. This pulse has a rise time of a few hundred ps, so will have a bandwidth in excess of 1 GHz.