attenuators

Am 04.06.2014 18:08, schrieb John Larkin:

Suhner have BNC attenuators and also a 50R feedthrough termination. If you blow the resistor you have what you want. I did it already unintentionally. :-) Still good for > GHz.

Cheers, Gerhard

(you can also open it and remove the resistor.)

Ummm... 0dB attenuator is called...wait for it...a feed-thru. But even that runs $42 from Pomona.

Thanks, but that's a termination. What I need is a straight-through connection, no resistors anywhere.

I designed a preamp for a photodiode. It hangs on two BNC females that are part of a vacuum flange on a fairly expensive (low 9 figures) machine. Now the pd is making too much signal, actually good news, but it's clipping my amp and ADC.

The easiest fix is to add an attenuator to the anode side of the photodiode, the signal side, but then I need a matching BNC male/female gidget to complete the cathode connection, the pd bias voltage. They have to be mechanically identical, or at least the same length.

Those are 75 ohm male connectors on your preamp. Is it a 75 ohm system?

The item shown is a feed through 50 ohm termination. If you can remove the resistor, then it will be a through connection but still it's 50 ohms.

Good luck finding a 0 dB pad in a series of like mechanical devices unless you modify one. That should justify additional cost for the value added.

Regards, tm

It's a 50 ohm system, but the bandwidth is low enough, around 100 MHz, that those flange connectors don't matter.

That would be a last resort, to buy an attenuator or a terminator and modify it. It would be interesting to see what's inside.

We call them "barrel connectors". Not sure if that is the industry standard terminology. We have a bunch of double-female BNC adapters, I know I have seen double male adapters somewhere. Not sure which flavor you need.

Jon

A male-female BNC is sometimes called a "connector saver." I guess I'll have to find one that's the same length as the attenuators.

I checked 5 different attenuator vendors. None of their attenuators are the same length.

I'd think you'd use a simple BNC coupler or bulkhead adapter for that. Unless you have a very specific need that it be exactly the same form-factor as the other attenuators?

On a sunny day (Wed, 4 Jun 2014 11:06:12 -0700) it happened snipped-for-privacy@coop.radagast.org (David Platt) wrote in :

I think 0dB or loss-less connectors are rare...

If it's spec'd down to DC then it's a continuous resistive plug forming a symmetrical resistor T, that's why either end can be I/O, among other things. A lot of the terminations just use a discrete 1-5W carbon resistor.

I would forget about the flange and use little coaxial jumper cables in the 6-12" range to fit your attenuator in and also get the plug/jack configuration right.

The darned preamp box hangs on the two BNC connectors on the flange; there is no other mechanical support. So the two BNC thingies have to be the same length.

I just milled open a Mini-Circuits HAT1-20.

Looks a lot like the SMA version...

Why not just eat the 1 dB?

Cheers

Phil Hobbs

That side is a photodiode bias supply, limited to 1 mA. I can't stand the resistance to ground.

I think because one of the BNCs is carrying bias voltage. If I understand right JL wants one BNC straight thru (with the pd bias) but exactly the same standoff length as the attenuator one with the signal.

piglet

A Mini-Circuits BNC attenuator is just about exactly the same length as four elbows in a row, by my measurement. That's if you can stand the extra width.

Cheers

Phil Hobbs

It sounds like you need to buy two off-the-shelf empty-box BNC-two-ends and populate one with a wire, the other with an attenuator.

The connectors on the flange are only 0.75" apart, so two of the usual Pomona boxes won't fit.

JFW Industries will make me a pair of BNC attenuators, one any value in 1 dB steps, and one "0 dB". The 0 dB one costs almost twice the regular one, $29 vs 17, probably because it's a special.