Question about making a coax jumper for use with an SDI video camera.

[JoshuaHufford]

I'm helping out on a project with a video conference setup that needs to be interfaced to a computer. The cameras use SDI connections over coax cable currently connected to a video switcher. The new addition will be an interface card so the system can be streamed over zoom.

This is the interface card that will be used, it has BNC and SMA connections.

https://www.amazon.com/Magewell-Capture-Dual-Video-Card/dp/B019M7Z98O

I need to make 2 coax jumpers that connect from the SMA outputs of the card to the BNC inputs of the video switcher.

This is the recommended coax from the camera and video switcher manufacturer,

1694A - 75 Ohm SDI Coax | Belden

75 Ohm SDI Coax, RG-6, 18 AWG, Solid BC, Foil + 95% TC Braid, PVC Jkt, CMR

catalog.belden.com

I already have some BNC and SMA ends for LMR-240. If I order some 75 Ohm 240 cable will this work OK? Or is there something special about this cable for video use?

Would I be better off just ordering some pre-made jumpers from the antenna farm or elsewhere?

 

[mmckenna]

The center conductor on LMR-240-75 is smaller than 50Ω LMR-240. Might be able to fake it, but you'd probably be better off with just getting some RG-6 and the right connectors. Since the RG-6 is going to be less expensive than the LMR-240-75, it may be cheaper.

Never worked with SDI, but when I was in college I worked with a lot of analog video systems and made a few thousand BNC cables. I found some pretty sketchy stuff that worked just fine for analog. Not sure if it would have passed muster with digital.

 

[JoshuaHufford]

OK thanks, I'll just order some jumpers.

 

[prcguy]

In the broadcast industry Belden 1505A and 1694A with Canare BNC connectors is fairly standard for SDI over coax. For a video conference setup I think a short run of most any RG-6 type cable would be fine. You don't want to use any 50 ohm cable.

 

[JoshuaHufford]

I need some more help here. I'm trying to find someone to make the 2 coax jumpers that I need and I keep running into dead ends.

The antenna farm does not stock any 75 ohm cable, at least that is what I was told this morning.

I tried MPD digital and they said that there are no 75 ohm SMA connectors, seems odd to me that the video interface card would have SMA outputs if there is no such thing as a 75 ohm SMA connector.

I simply need 2 coax jumpers that connect to the loop out of the interface card in the PC, the card has female SMA connections, to the video switcher that has female BNC connectors. The coax needs to be 3 ft. long.

Where can I get these made, or what is the best way to accomplish this? Do I need to use adapters?

 

[chief21]

How about a standard 75 ohm BNC to BNC patch cable with a BNC/SMA adapter on the card end?

 

[JoshuaHufford]

I thought about going that route, however I didn't know if 50 Ohm adapters will work, and I haven't been able to find 75 ohm adapters.

 

[JoshuaHufford]

Well I did just find this, but the price!!!

SMA Male to BNC Male Cable 36 Inch Length Using 75 Ohm RG59 Coax

SMA Male to BNC Male Cable 36 Inch Length Using 75 Ohm RG59 Coax from Pasternack has same day shipment. Pasternack SMA Male to BNC Male Cable 36 Inch Length Using 75 Ohm RG59 Coax is offered in custom lengths as well. SMA Male to BNC Male Cable 36 Inch Length Using 75 Ohm RG59 Coax or custom...

www.pasternack.com

 

[chief21]

Well I did just find this, but the price!!!

Yikes! Probably better to try the inexpensive BNC cable/adapter approach. I wouldn't expect the adapter to be an issue at video levels. If it isn't acceptable, you can always buy something special-made.

 

[JoshuaHufford]

My main concern is any physical size differences between 75 ohm and 50 ohm connections. I don't want to mess up the connections on a $600 card.

 

[prcguy]

My main concern is any physical size differences between 75 ohm and 50 ohm connections. I don't want to mess up the connections on a $600 card.

A 50 ohm and 75ohm BNC connector are completely interchangeable with the same pin size.

 

[prcguy]

SMA to BNC adapters are 50 ohm only and its not a big deal to use in a 75 ohm system below several hundred MHz since the adapter is a very small fraction of a wavelength.

I thought about going that route, however I didn't know if 50 Ohm adapters will work, and I haven't been able to find 75 ohm adapters.

 

[JoshuaHufford]

SMA to BNC adapters are 50 ohm only and its not a big deal to use in a 75 ohm system below several hundred MHz since the adapter is a very small fraction of a wavelength.

That is what I needed to know!

Thanks so much!

 

[JoshuaHufford]

So I discovered on the webpage for the capture card that it actually comes with SMA to BNC adapter cables, specifically these,

SDI to SMA cable | Mobile Video Devices Inc.

The suitable cables and breakouts are included with the purchase of Magewell capture products. The cables and breakouts are also sold standalone. SDI to SMA cable This particular cable is for: Pro Capture Dual SDI XI200DE-SDI (discontinued) XI104XE-HD (discontinued)

mobilevideodevices.com

So all I need is two 75Ohm BNC patch cables and we are good to go.

 

[mmckenna]

So all I need is two 75Ohm BNC patch cables and we are good to go.

Any place that sell semi-professional video gear should have those.
I can't even begin to count how many thousands of those I made back in my younger years.

 

[JoshuaHufford]

Any place that sell semi-professional video gear should have those.
I can't even begin to count how many thousands of those I made back in my younger years.

Yeah those are easy to find and I already have them ordered.