Coax communication frequency

[Honi]

What is the frequency of the communication over the coax cable?

[Daniel Aharoni]

Hi Honi,
There are 2 frequency bands being sent simultaneously over coax. One sits around 1MHz and handles the back communication such as I2C. The other is on the order of a few hundred MHz and handles data transmission. If you need exact frequency values let me know and I will calculate them.

The hardware is capable of supporting up to 1.4Gbps.

[Honi]

I'm planning on using a commutator and wanted to check to make sure that one with a 3GHz pass band would work. 

[Daniel Aharoni]

All the communication and data transmission will be below 3GHz. One other thing to be concerned with when looking into commutators is their impedance. Ideally you want a 50Ohm impedance commutator. If you cannot find one of those, make sure any non-coaxial cabling is as short as possible and that the wiring inside the commutator is relatively short.

We have been using commutators from DragonFly with great success. Their commutators are not specs for 50Ohm impedance but they still work great as long as we keep any non-coaxial cabling as short as possible.

[Honi]

Ok.  I found 50Ohm coax commutators that are cheaper than the dragonfly one and will let you know how it goes. 

[Daniel Aharoni]

Great Honi. One other thing to consider is the amount of torque required to turn the commutator. I imagine most commercial commutators will be fine but one nice thing about the DragonFly commutators is they are really low torque.

[rnleao]

Hi Honi,

any luck with your coax comutator? Thanks

Richardson

[Honi]

We have found CRJ-05 to work fine for rats. It requires a bit of starting torque (~0.4N*cm), so may not work for mice. It is designed for high frequency coax communication though. The quote we received was ~$250. http://www.barlintimes.com/product/coax-rotary-joint/high-frequency-rotary-joint.html

[ONECore]

Instructions for an inexpensive passive commutator tested with the Miniscope can be found: https://optogeneticsandneuralengineeringcore.gitlab.io/ONECoreSite/projects/SlickPassiveElectricalCommutator/