Questions relating to HD-SDI cables / remote trigger in nanoflash application

[Mike Sertic]

I have a nanoflash on pre-order that I am planning to use in a marine/POV environment where the recorder and camera would be located in different housings, connected by a cable (or cables) carrying power to the camera and the video signal (over HD-SDI) back to the camera.

Having never dealt with HD-SDI cables, I have been trying to look into how I would actually do this. The only thing I have been able to find so far is that the HD-SDI standard specifies a nominal impedance of 75 ohms and that cables that don't meet this spec may result in signal dropout. Not being much of an electrical engineer, I am under the impression that it is pretty easy to change impedance by adding resistance (such as a solder joint) or changing cable length, but I'm not really sure.

Regarding the cabling, does anyone have experiencing splicing/soldering HD-SDI cables or carrying the signal over a non purpose-built cable? The ideal situation would be to run power and video through a single cable between the housings and break out the power and video connectors on each side.

Failing that, I will still have to run the cables through waterproof bulkhead connectors, which we have done in the past with SD composite video cables by just cutting the cable at one end, running the cable, then splicing inside the recorder housing. If I can't do this and stay in the impedance spec, does anyone have a lead on a supplier who can manufacture a cable with the bulkhead connectors (supplied by me) added in-line on the cable before the BNC connectors are put on?


Also, regarding the provision for the remote trigger, based on the published specs it looks like this would be fairly straightforward to wire something up, but is convergent design or anyone else planning to offer a remote switch for sale?

[Dan Keaton]

Dear Mike,

First, lets speak in general terms:

When working with HD-SDI, quality cables are a must, and they should be 75 ohm and the BNC connectors should be 75 ohm. For long distances, this is an absolute must, as is a single cable without any splices or barrel connectors.

(Yes, one can substitute a 50-ohm cable for very short distances, but this is not recommended. Quality BNC connectors help protect your investment in your nanoFlash.)

HD-SDI cables must not be sliced and soldered. The signal is 1485 Megabits per second or 1.485 Gigabits per second. No, in my opinion, adding a resistor will not work.

We will be happy to build custom cables for you. I do not know of a combination signal/power cable that meets HD-SDI specs. But, we need to know the desired length of your cable.

Now, for specific advice:

It appears from your questions that the camera will be in one underwater housing and the recorder in another, but only separated by a few feet.

If this is so, you may get by with "Siamese" cable, a cable with power and signal on separate conductors. Just get some in 75-Ohm impedance if possible. If you are less than 10 feet this may work. (I can't tell you the actual distance that it will and when it won't work, it just depends on the cable and the connectors, etc.)

HD-SDI is sent as a digital signal. Generally, it either works or it doesn’t.

Yes, we will build whatever you need.

My email is: Dan @ Convergent-Design (dot) com

Just remove the spaces and convert the (dot) to a “.”.


We do offer remote switches for sale, and we can custom build them to meet your needs, such as including an additional set of leads for a underwater switch built into your housing.

We just built some for a major underwater expedition and we will be happy to help you.

[Mike Sertic]

Thanks Dan, cable length is going to be four feet or so.

I will follow up by email with more specific info.

[Bill Ravens]

Mike...
I have a FlashXDR that I carry on my shoulder while shooting with a JVC HD110 camera. I power the FlashXDR from the onboard camera battery, which is usually an AntonBauer Dionic 90 battery. The FlashXDR is interconnected to the camera via a 4-pin XLR power cable, an HD-SDI cable, and a remote trigger cable. All three cables are 7 ft long, and all are hi-quality shielded cables. I keep the cables bundles with a single automitive, plastic, cable wrap/protector. The configuration works very well.

[Dan Keaton]

Dear Mike,

Since the cable is only going to be 4 feet or so, this will be easy.

I recommend a high quality HD-SDI cable, with appropriate connectors (all 75 Ohm would be best), and a separate power cable, which we could bind together.

This could be attached to the HD-SDI cable in a variety of ways. I would recommend that we just put some shrink wrap every so often to keep the cable together.

I like Bill's idea, but it could fill up with air and might create a problem when you submerge it. On the other hand, water may just fill up the wrap without a problem.

We could shrink wrap the whole assembly, except for the very ends.

We would need to know more about the connectors that you want to use.

[Mike Sertic]

The camera (Toshiba IK-HR1S) uses the same power connector as the nanoflash (Hirose HR10A-7P-4S). The power cable would split off inside the recorder housing to connect to the nanoflash and the battery. The battery to power cable connector can be anything, we will probably have a custom NiMH or Li-polymer battery pack made, so we will have bare leads to wire to.

Having the two cables bundled with shrink tape will work fine. We have built similar helmet camera systems with SD cameras, and we found that it is better for the cables to be somewhat stiff - they lay better and are less likely to be damaged by bending too much, so a layer of shrink tube on the whole length would be ideal.

Can you tell me what the diameter is for HD-SDI and power cables you would use? I would need this to source the waterproof pass-throughs.

Also, if you have any pictures of the remote switches you have built, that would be helpful. We would want the remote to be as small as possible and have the switch and indicator LED on the end of a flexible 3 foot cable.

[Dan Keaton]

Dear Mike,

In both cases, the power cable, and the HD-SDI cable, the connectors have a larger diameter than the cable itself.

For your application we could use Canare LV-61S (a very flexible HD-SDI cable)
(remember that as we add another cable and shrink wrap it will become less flexible).

Canare Corp. - Quality Cables and Connectors: Product Item Display

If you want to use a stiffer cable, then we would use Canare L-4CFB.

Canare Corp. - Quality Cables and Connectors: Product Item Display



For the Canare LV-61S, the nonimal outside diameter is 6.1mm.
The proper Canare BNC Connector is BCP-C4B, with a diameter of 14.5 mm.

For the Canare L-4CFB, the nonimal outside diameter is 6.1mm.
The proper Canare BNC Connector is BCP-C4F, with a diameter of 14.5 mm.


Here is a link to the connectors which will show you the dimensions of both connectors

Canare Corp. - Quality Cables and Connectors: Product Item Display


Cable Boots

When we build our custom cables, we always build them with cable boots (unless the overall length of the cable precludes the use of cable boots).

These cable boots protect the connector ends of the cable from excessive bending and increase the reliablity of the cable assembly.

Canare Corp. - Quality Cables and Connectors: Product Item Display



For the power, we are very familar with that specific Hirose connector.

The diameter of this connector housing is larger than the diameter of the cable that we use. The maximum diameter of this connector is 11.5 mm while the cable diameter is 4.7 mm (I believe as I do not have access to the specific belden cable number that we use at this moment, but it is under 5 mm in diameter.)

Here is a link to a picture of the connector.

http://rocky.digikey.com/WebLib/Hiro...R10A-7P-4S.jpg

Here is a link to the Hirose page: (your connector is located on page 65)

http://www.hirose.co.jp/cataloge_hp/e11000216.pdf


Please note that if you decide to make you own cables, the proper cable stripping and crimping tools are required.


For all dimensions, please allow room for the shrink wrap.


Here is a link to the illuminated LED remote control switch we use:

SWITCH PB ILLUM SPDT MOM RED - KB15CKW01-5C-JC


I have some questions for you:

1. Will you want the cables and remote control fully assembled and you will thread them thru a waterproof bulkhead connector?

2. How will you use the remote control? It is not waterproof.
We can provide bare leads from the remote control for you to wire to a switch located inside of your waterproof housing.

We can assist in the design of a switch that will work inside of your waterproof housing, activated by your diver.

3. By "Marine/POV", I am assuming that you mean underwater. Is this correct?


Please note that the Hirose power cable may need a connector on only one end, so only the cable may need to go through a waterproof bulkhead connector.

[Mike Sertic]

Dan,

Thank you very much for the help you have provided so far. I sent you an email at the address provided below.

-Mike