bigglesuk Posted July 2, 2007 Share Posted July 2, 2007 I need to order some 50 ohm BNC connectors from Canford Audio for panel I'm making. The panel will be extending some Sennheiser radio mic aerials to a rear panel on a rack. I've found various BNC male connectors on the Canford site but they don't reference RG58 (the cable I have). Any ideas of the right one? I just search on their for 50 BNC. Also, what's the best way to lay the rear panel out? I have a standard 16 way d type 1U panel and need to load 4 x BNC sockets (for two radio mic receivers), 1 x Power con and 2 x XLR males into it. How should the spacing on the aerials go? Thanks, Adam Link to comment Share on other sites More sharing options...
mackerr Posted July 3, 2007 Share Posted July 3, 2007 I need to order some 50 ohm BNC connectors from Canford Audio for panel I'm making. The panel will be extending some Sennheiser radio mic aerials to a rear panel on a rack.If you think you may want to remote the antenna away from the rack, you may want to consider using RG59 instead of RG58. There will be an impedance mismatch, although it is not that critical as is explained in this thread. When extending the cables to remote the antenna RG58 will have too much loss to be useful. If you go with 50ohm cables within the rack you will need 50ohm cable to extend, and that will mean large diameter low loss cables like RG8, or LMR400. If you go with 75ohm within the rack you can use RG59 which has much lower loss at the UHF frequencies common in wireless mics. Mac Link to comment Share on other sites More sharing options...
bigglesuk Posted July 3, 2007 Author Share Posted July 3, 2007 I went for 50 ohm cable as the specs on the Sennheiser website mention 50 ohm. The cable I have is RG58C/U 50 Ohm coaxial cable from VDC that they say "Also commonly used for radio microphone aerial connections". Should I be using 75 ohm RG59 cable? As for moving the antenna away from the rack, we will have 4 small antennas on the back of the rack so can't really move them away from the rack, we unfortunately don't have the money to get one of the aerial distribution units. Adam Link to comment Share on other sites More sharing options...
paulears Posted July 3, 2007 Share Posted July 3, 2007 No - you're right. Current feeling is that it's perfectly ok to use RG59 75 Ohm cable as the mis-match on a short run isn't really going to be noticable. RF equipment has 50 Ohm specs as 'normal'. One thing that is important is to use the correct connectors. While 50 and 75 Ohm connectors look superficially the same, and will mate, 50 Ohm plugs have a larger centre pin, 75 Ohm versions look different. Although you get away with it a few times, plugging big pin plugs into sockets expecting a smaller pin, bend the contacts a little, and after a few mate/unmate cycles, a 75 Ohm plug inserted into a 'stetched' 75 Ohm socket isn't reliable. A small pin in a socket expecting a larger one can also result in intermittent contact. The faults show up as annoying little faults that often go away when the cables are wiggled. Always worth watching for this mismatch when using adaptors, sometimes these are not marked that well, and you need to examine them carefully. Link to comment Share on other sites More sharing options...
Andrew C Posted July 3, 2007 Share Posted July 3, 2007 One thing that is important is to use the correct connectors. While 50 and 75 Ohm connectors look superficially the same, and will mate,Don't Canford have something contradicting this in the back of their book? Ahh, and on line too! PDF It is implicit in IEC 169-8 that 75 ohm BNCs made to comply with that standard will mate in a non-destructive manner with the 50 ohm BNC connectors described in IEC 169-8. All BNC connectors supplied by Canford as stand-alone connectors are compliant in that respect with the IEC standard. In over 15 years and a many million BNC connectors we have no first hand experience of incompatibility between 50 ohm and 75 ohm types, other than extremely rare (and very obvious) manufacturing faults. Link fixed Link to comment Share on other sites More sharing options...
paulears Posted July 3, 2007 Share Posted July 3, 2007 Yep, contacts with proper wiping surfaces are secure on both - the snag comes with the pattern versions that are about. The moulded cheaper BNCs sold as video cables are ones that cause trouble. In fact the other way around can be pretty annoying - they can jam. The cheaper 75 ohm sockets can bind on 50 Ohm plugs - I've had this problem a few times. The worse ones I've found are when you extend a cable with a BNC back-to-back adaptor - if you have any of the cheaper ones (the dodgy ones I have are unbranded, and appear to be plated, rather than aluminium) - have a close look at the contact in the centre - it's very thin, and makes contact via a very slim 'V' shaped pressing. Stick a 50 Ohm plug into these, and then remove it and you can see they have to bend quite a way. Most chassis mount sockets are from more 'secure' sources, but some of the BNCs on lesser well known products can be foreign cheaper types, so despite the IEC standard, it's worth checking if you find loose connections. Link to comment Share on other sites More sharing options...
bigglesuk Posted July 3, 2007 Author Share Posted July 3, 2007 So if I got some of these http://www.canford.co.uk/commerce/productd...roductid=48-503 then they would work? Also, when mounting the aerials on the back, should I space them out just like they would be on the back of the receivers. Or should I put the first aerial from both receivers towards one end of the panel and the second aerial from both receivers down the other end? --A1-----A2------B1------B2-- or ---A1--A2----------B1---B2-- Cheers, Adam Link to comment Share on other sites More sharing options...
paulears Posted July 3, 2007 Share Posted July 3, 2007 diversity needs distance between the A and B antennas, so go for max spacing. If they are close, the advantages of diversity are lost. Link to comment Share on other sites More sharing options...
bigglesuk Posted July 3, 2007 Author Share Posted July 3, 2007 I'm an idiot! I meant to type the following: - --A1-----A2----------B1-----B2--------- (Two receivers side by side would be like that) ---A1--B1-------------A2----B2-------- (One aerial from each receiver at either end) So your suggesting the second layout? Link to comment Share on other sites More sharing options...
paulears Posted July 3, 2007 Share Posted July 3, 2007 yep, that's the way to do it! The two aerials on the back of most receivers aren't really far enough apart to work properly. When a signal is weak and starts to hiss badly. Moving a single aerial 150mm or so (the distance between the sockets on the back), makes little difference, trebling the distance is worthwhile and improves the stability quite a bit. I've seen some racks where sockets one end are remoted to more distant clip on aerials, on separate cables - separating them even more. Link to comment Share on other sites More sharing options...
bigglesuk Posted July 3, 2007 Author Share Posted July 3, 2007 Thanks Paul, I know how to sort it all out now ) Adam Link to comment Share on other sites More sharing options...
bigglesuk Posted July 17, 2007 Author Share Posted July 17, 2007 Arrrrrgggghhhh.... I'm going mad. Can anyone help me with the following? When I search on Canfords website for "50 ohm" I get a load of stuff back. The BNC connectors are all listed with a 'group' code. Does anyone know which group code would be compatible with standard RG59 cable? I don't want to buy the wrong connectors. Adam Link to comment Share on other sites More sharing options...
mackerr Posted July 17, 2007 Share Posted July 17, 2007 When I search on Canfords website for "50 ohm" I get a load of stuff back. The BNC connectors are all listed with a 'group' code. Does anyone know which group code would be compatible with standard RG59 cable? I don't want to buy the wrong connectors. AdamWhy do you want 50 ohm BNC connectors to go on 75 ohm RG59? Mac Link to comment Share on other sites More sharing options...
bigglesuk Posted July 17, 2007 Author Share Posted July 17, 2007 Why do you want 50 ohm BNC connectors to go on 75 ohm RG59? MacOops, that was a typo! Meant RG58! I just did a completely different search on Google and it seems that Group C is suitable for RG58. If anyone is interested this page gave me a lot of info and may be of use to people Adam Link to comment Share on other sites More sharing options...
The Wigawam Posted July 25, 2007 Share Posted July 25, 2007 Have you tried RS Components? - lots of useful cable and connection info and data sheets or maybe try Maplin (probably cheaper than Canford) both RS and Maplin are on-line. Link to comment Share on other sites More sharing options...
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