Change BNC connectors

[dtcallcock]

Sampler is the only place in Sinara where one is forced to use BNCs and an 8HP panel.

Standardising all boards to 4HP may be advantageous for a future backplane.

MMCX would be an obvious choice as we are already using it for the Sayma v2 AFE analog inputs and Stabilizer aux digital inputs. However, they are a bit on the small side and easy to disengage compared SMB/MCX so one might worry about mechanical robustness. SMC/Micro BNC/LEMO all seem somewhat less ubiquitous and more expensive. My slight preference would be for MCX, but it would be good to hear from people with more experience. I'm not totally sure how you would isolate this kind of connector from the front panel though (just a clearance hole?).

Even if we all agreed this is a brilliant idea, it probably doesn't warrant a board revision right away. I did want to leave an issue open in this repository for future reference though.

[dhslichter]

Just need to think a little about crosstalk (granted, BNC is not great for this either). But I agree that MCX or SMB or other smaller connectors would be nice.

[dtcallcock]

@hartytp makes the point that:

Personally, I also like BNCs. Much quicker to swap in and out. Much easier to make ones own cables to length quickly and cheaply.

It seems that MCX is even easier to swap in and out than BNC and connectors are available that, at first glance, don't look any harder to assemble than a BNC connector (eg. this RG-316 connector).

However I do buy the argument that most labs have a lot of BNC stuff around and a proliferation of random connectors across Sinara should be avoided (hence my opinion that we should just pick one general BNC replacement). The board could also optionally ship with 8 BNC pigtails.

Just need to think a little about crosstalk (granted, BNC is not great for this either).

A random search suggests that MCX might have >70dB RF leakage (compared to >100dB for an SMA and >55dB for BNC). MMCX seems similar to MCX and SMB seems similar to BNC. Exact numbers depend on mfg/cable obviously.

[dhslichter]

SMB leakage is lousy, so I generally don't like them. If MCX is better then rock on.

[dtcallcock]

Btw, we have one of these Seeed mini-scopes with MCX connectors on it and they seem pretty nice to me.

It shipped with the kind of BNC pigtails that @gkasprow mentioned. I also found some SMA adaptors that enable use of standard SMA cables, but at high density (as one doesn't have to leave room for the torque wrench).

[gkasprow]

DSO203? I have such model for 4 years or so and can confirm that these probe connectors work reliably.

[jordens]

Could be my "DSO Quad" and would be 6 or 7 years old now.

[gkasprow]

The assembly house asked us to make some cosmetic changes that would improve the production yield.
I will also add mounting holes for CPCIS adapter. Do we plan to change the BNC connectors and switch to 4HP?

[gkasprow]

MCX version would look like this

[hartytp]

I’m happy with either BNC or MCX

[jordens]

Go for mcx.

[gkasprow]

Do you want MCX-BNC adapters to be delivered with Sampler?
Would such cable be fine?

They cost roughly 2EUR/pc

[jordens]

Ah. One thing to check: those small mcx to sma bullet adapters. Do they fit or is the pitch to small for sma?
Yes. I'd include 8 of those pigtails.

[gkasprow]

I tried with the biggest SMA-MCX adapters I could find and it will work. Of course, SMA needs to be attached prior to plugging. I do not recommend using these adapters with thick and long SMA cables because they will add tension to the MCX connectors and the PCB. Cable adapters seem to be a better choice.

[gkasprow]

There is no collision with the handle

[dtcallcock]

+1 for MCX and pigtails

[hartytp]

@gkasprow @jordens and others, do we want to do anything here for the next revision, or leave this to further down the line? I'm okay with MCX so long as we ship with MCX to BNC pigtails.

[gkasprow]

The Sampler board can be ordered with MCX adapter board, so I'm leaving it as it is now with BNCs.

[dtcallcock]

Added note about this to wiki.

[gkasprow]

Btw, one can already order such Samplers. TS did a production run AFAIK.