Here's what I'm trying to do: I have a Q-See QT View camera system with 8 inputs. The system is designed to run 4K cameras over the old coax/12V dual cable from old analog camera systems, and works well. It saves having to re-run cables when upgrading from an old analog camera system to a new digital system. I believe it's now sending a digital signal over the coax cable. Various manufacturers have the same setup, although I doubt they use a standard (interchangeable) protocol.

What I'd like to do is be able to take 1 input and electronically switch between 2 camera feeds. Switching would be infrequent, but would need to be done remotely (no human activated switch). If it was just a straight digital signal, I could probably just use a relay. But given that the signal is being sent over coax and has got to be a fairly high frequency signal, I'm guessing that a relay wouldn't work.

Any suggestions on how to accomplish this would be appreciated. I have no problem providing the control signal to drive the switching circuit, just have no idea what would be involved to build a circuit that would electronically pass one feed or the other feed. When it comes to transmission lines (which I'm guessing the 50 or 75 ohm coax is) I'm out of my depth.

Thank you.

 

Without knowing more about the amplitude and bandwidth of the coax signal, it's hard to recommend a chio=p or circuit. There are coax relays, a normal-type relay coil with BNC connectors as signal contacts and better than average but not perfect impedance control through the armature and contacts. probably expensive.

Digi-Key has "high-frequency relays" that could work.
https://www.digikey.com/en/products...-rf-relays/963?s=N4IgTCBcDaIE4FMA2BDAniAugXyA

Or, try this:
https://www.ebay.com/itm/2024888824...044&customid=9c33c19000a818d42ffea553d585b3dc
https://www.ebay.com/sch/i.html?_from=R40&_nkw=coax+relay&_sacat=0&_sop=15

Near-perfect signal integrity, stupidly expensive:
https://www.pasternack.com/low-power-a-b-coaxial-electromechanical-relay-switches-category.aspx

What voltages are available to power the relay and control circuit?

ak

 

What voltages are available to power the relay and control circuit?

The overall control circuit has a 12V supply, and I'm using an ESP32 for the web interface so I have 12V, 5V and 3.3V to work with. I'm looking at the HF relays on digikey you referenced and it's worth mocking something up to see if one will work.

Finding the bandwidth has been a good question. Numerous searches and camera datasheets have not yielded any useful information.

Thanks.

 

A coax (BNC) type relay should work, but they appear to be rather expensive (several hundred US dollars).
You might be able to find a used one for a reasonable price.

 

DK has a bunch of them in their system for around $30-50, but they're all obsolete and out of stock. Smells like ebay.

ak

 

I picked this up on ebay:

https://www.ebay.com/itm/265841867475

Took a bit but was able to find specs on it. We'll see how it works. Thanks!

 

I picked this up on ebay:

Those look like SMA coax connectors, so you may have to buy adapters to connect to the coax connectors on the cables.
Do you know what type of connectors they are?

 

Those look like SMA coax connectors, so you may have to buy adapters to connect to the coax connectors on the cables.
Do you know what type of connectors they are?

Yes, that's the easy part. Already have adapters to go from SMA to BNC.

 

Yes, that's the easy part. Already have adapters to go from SMA to BNC.

Great.
Then you should be all set.