david.elsbury Posted January 7, 2016 Share Posted January 7, 2016 I would have thought crimped male ends that plug into female-female panels should be fine. Pretty common patchbay fare. Normally the crimp tools are fairly generic and it the ends that can be specific to the type of cable. Link to comment Share on other sites More sharing options...
TomHoward Posted January 7, 2016 Author Share Posted January 7, 2016 Thanks. The cable we have got is pretty big (1.65mm core with 10mm OD) so I am going to have to look a bit closely at the tools and connectors. Passthrough will no doubt be easier but I am expecting they will need a deep wall box - so will need some digging into walls I reckon. Link to comment Share on other sites More sharing options...
alistermorton Posted January 8, 2016 Share Posted January 8, 2016 Solder, if done properly, should be fine at video over BNC frequencies. If always was when we did it at EMI Link to comment Share on other sites More sharing options...
david.elsbury Posted January 8, 2016 Share Posted January 8, 2016 Er but Alister we're not talking about "BNC frequencies" (whatever imaginary things those are?) we are talking about fairly high bandwidth HD-SDI or 3G-SDI Link to comment Share on other sites More sharing options...
alistermorton Posted January 8, 2016 Share Posted January 8, 2016 If we are talking about using BNC connectors then I'm assuming we're talking about frequencies that BNC connectors are rated at. If the Signal is at a higher frequency than a BNC connector is (typically) rated for then it's the wrong connector for the job, surely? Link to comment Share on other sites More sharing options...
david.elsbury Posted January 8, 2016 Share Posted January 8, 2016 Do you know what SDI even is? http://www.commspecial.com/assets/applicationnotes/SDI%2010%20Things.pdf Check out no7...As any video engineer will tell you, signal delity is all about bandwidth. If the transmission system doesn’t have enough bandwidth required by the video signal then the resulting image will be distorted in one or more ways. Usually detail or resolution is lost but other distortion will surface too. With composite video, signal paths of 10 MHz were considered more than satisfactory to pass NTSC or PAL virtually distortion-free. But with SDI, transmission bandwidths into the gigahertz range may be needed. Consider standard de nition SDI, the digital serialization of NTSC or PAL, which is a 270 Mbps signal. Then there is HD-SDI for 1080i and 720p, which is a 1.5 Gbps signal, and 1080p, which is twice that at 3 Gbps. These very high-speed signals require much thicker coax cable that has less signal loss or even ber to adequately transmit them over the distances common in professional video. Link to comment Share on other sites More sharing options...
alistermorton Posted January 8, 2016 Share Posted January 8, 2016 BNC are typically specced up to 4 GHz before the losses start to degrade the signal too much. An N-type is typically rated for higher frequencies - in excess of 10 GHz (we used to use them on microwave test sets and they were soldered as well as crimped). Link to comment Share on other sites More sharing options...
david.elsbury Posted January 8, 2016 Share Posted January 8, 2016 I don't think the connector choice is an issue- I am doubtful that soldered connections have the edge over crimped ones :-) Link to comment Share on other sites More sharing options...
TomHoward Posted January 8, 2016 Author Share Posted January 8, 2016 Looking at this coax I think I'm going to do it slightly differently, as terminating 10mm coax into a wall boxes and patchbay is going to be a nightmare, I'll do the main of the run in the big coax and add a connection and short tail into each end to do the patchbay & wall boxes, otherwise I'll be digging half the wall out to get the box on.Shouldn't be any more terminations than a pass through as I can use a panel crimp to minimise at the panels & patchbay and then inline either BNC or N or something else just to change cable size. Hopefully will be okay. Longest run is about 50m so I'll test double that with a couple of terminations to make sure. Link to comment Share on other sites More sharing options...
alistermorton Posted January 8, 2016 Share Posted January 8, 2016 Crimps, in theory, being a cold weld, /ought/ to be better than solder. However I suspect that in a lot of manufacturing procedures crimps are preferred because they are easier to do mechanically rather than being more reliable. Link to comment Share on other sites More sharing options...
TomHoward Posted January 8, 2016 Author Share Posted January 8, 2016 The BNC solder connectors I'm talking about as well are the neutrik panel type rather than inline, this style http://cpc.farnell.com/productimages/standard/en_GB/42392124.jpg It's rated up to 3GHz apparently but the lack of shielding around the termination seems to be a bit of a weak point to me compared to a crimped connection, which would maintain the shielding. Am I right in that or is such a small section not a concern? Obviously less of a difference in a solder vs crimp cable connector, where it's really only if the pin is soldered or crimped, and the outer is crimped or compression, but in either style the shielding is still maintained Link to comment Share on other sites More sharing options...
timsabre Posted January 8, 2016 Share Posted January 8, 2016 It's rated up to 3GHz apparently but the lack of shielding around the termination seems to be a bit of a weak point to me compared to a crimped connection, which would maintain the shielding. Am I right in that or is such a small section not a concern? It's not "shielding" you need to worry about but the impedance of the joint. I do not pretend to be an RF expert but as I understand it, with high frequency signals changes in the physical structure of the connection can appear as short circuits to the signal (same if you crushed part of the coax even if there isn't an electrical short at DC). The crimp connectors maintain a more uniform physical arrangement so there is less of an impedance mismatch. It's the same with RJ45 panels, you need to maintain the correct twist of the cat5 cores right up to the termination or it affects the impedance of the connection. The "rated frequency" of the connector is a bit of a red herring as the impedance of the connector gets progressively lower as the signal frequency gets higher. There isn't a magic point at which it stops working. Link to comment Share on other sites More sharing options...
TomHoward Posted January 8, 2016 Author Share Posted January 8, 2016 Thanks again. I am going to rig up a test line with longer main length than we will need, and the joints down to more flexible coax at both ends. Average runs are about 30m but there's a couple of longer one-offs at about 60m. Going with crimped panel sockets, and crimped inline males and female BNCs to make the join inside the trunking to smaller coax for the termination at both ends. Link to comment Share on other sites More sharing options...
david.elsbury Posted January 8, 2016 Share Posted January 8, 2016 I'm sure that sort of run will be fine - let us know how you get on :) Link to comment Share on other sites More sharing options...
TomHoward Posted January 10, 2016 Author Share Posted January 10, 2016 So just a question, we're speccing for 3GHz cable and connectors and lengths for proper 3G-SDI, but in practice our camera planned is 1080p at 30fps. Reading up on SDI, HD-SDI will run 1080i at 60fps using 1.5GHz bitrate, and 3G-SDI runs 1080p at 60fps using 3GHz bitrate, but I can't figure if 1080p at 30fps will result in a 1.5GHz bitrate or whether it'll still run at 3GHz and just have some redundancy? Not really a major issue as we'll spec and hope for 3GHz compatibility anyway but just out of interest. Link to comment Share on other sites More sharing options...
Recommended Posts
Archived
This topic is now archived and is closed to further replies.