ShipsWoofy
Well-Known Member
<u>Fitting a BNC connector.</u>
It is always difficult to post definitive ‘how to’ posts to the forum, someone always picks faults with your method. But I will take the plunge and hopefully someone will find this post useful.
As it happens I actually had the wrong sized BNC connector for the coax I was using on the day, the backing screw on the connectors come in different cable sizes, this means in this case I had to ‘whittle’ the coax insulation a little to allow the backing screw to slide over it. Had I had the larger size in my toolbox this would be unnecessary. For the purpose of this exercise it is not important; the following instructions will not refer to this problem again.
1. What’s in the bag?
A 50ohm BNC clamp plug from Maplin, Link to maplin
If your application is navtex then you will probably require the 75ohm connector, check in the manual.
Laid out in order of fitting, check you have all these components.
Backing screw – washer – spacer – ferrule – pin – front connector assy
(These are my descriptions, they may have official names)
2. Fitting the connector.
The first job is to strip back the outer insulation on the coax. About the length of the assembled connector will do, trimming can be done later. I use a surgical scalpel, try not to cut too deep as you will damage the braid, the insulation is soft, just work it round in your fingers while you apply gentle pressure on the scalpel. Once you are through you can pull off the insulation leaving it as above.
Slide the backing screw over the braid and onto the cable, roll back the braid to expose the inner. Now, slide over the inner, the washer, spacer and ferule. Strip back the inner with the scalpel so it is just proud of the ferule, see below.
Snip the inner so that it fits snug into the pin bucket, the wire should reach the end of the pin, but when fitted the pin should be touching the insulation, no inner wire should be exposed between the pin and insulator.
3. Soldering
Sorry about the focus
We need to tin the inner, you will find the insulation will melt easily, so practice tinning wire on scraps you have around before doing this. The reason for leaving the inner insulation just proud is to allow for a small amount of shrink. When you become proficient at soldering you should be able to reduce this shrink considerably.
Now we need to add solder to the pin. Turn the pin upside down to expose the bucket, here I have stabbed it into the bottom of a tissue box to hold it while I work. Hold the iron against the bucket and allow time to heat up, when the bucket reaches a the right temperature the solder will flow, you do not put solder to the soldering iron tip, you apply it to the bucket.
Once you have solder in the bucket, hold the iron against the bucket and wait until the solder melts. Upon melting, bring in the coax and slide it in, remove the iron and allow to cool. Do not be tempted to dip in water or a wet sponge as this will weaken the joint, gentle blowing on the joint is fine.
Reassemble the components as above.
Trim the braid, but not so much that it is flush, you want to trap braid within the threads when you screw the connector front to the backing screw. Here I could have probably allowed a little more length of braid to be exposed. Important – Check for stray braid, a single wire from the braid to the pin can short your connection and damage equipment. Measure across the pin to braid with a multimeter on resistance, a dead short may indicate a problem, even with an RF antenna connected you should get a few ohms not a dead short i.e. 0 ohms.
Assemble the plug and tighten. Important – hold the back screw still with the spanner and screw on the front part, screwing the back screw at this point will tear the braid.
The finished job.
Hope it helps......
It is always difficult to post definitive ‘how to’ posts to the forum, someone always picks faults with your method. But I will take the plunge and hopefully someone will find this post useful.
As it happens I actually had the wrong sized BNC connector for the coax I was using on the day, the backing screw on the connectors come in different cable sizes, this means in this case I had to ‘whittle’ the coax insulation a little to allow the backing screw to slide over it. Had I had the larger size in my toolbox this would be unnecessary. For the purpose of this exercise it is not important; the following instructions will not refer to this problem again.
1. What’s in the bag?
A 50ohm BNC clamp plug from Maplin, Link to maplin
If your application is navtex then you will probably require the 75ohm connector, check in the manual.
Laid out in order of fitting, check you have all these components.
Backing screw – washer – spacer – ferrule – pin – front connector assy
(These are my descriptions, they may have official names)
2. Fitting the connector.
The first job is to strip back the outer insulation on the coax. About the length of the assembled connector will do, trimming can be done later. I use a surgical scalpel, try not to cut too deep as you will damage the braid, the insulation is soft, just work it round in your fingers while you apply gentle pressure on the scalpel. Once you are through you can pull off the insulation leaving it as above.
Slide the backing screw over the braid and onto the cable, roll back the braid to expose the inner. Now, slide over the inner, the washer, spacer and ferule. Strip back the inner with the scalpel so it is just proud of the ferule, see below.
Snip the inner so that it fits snug into the pin bucket, the wire should reach the end of the pin, but when fitted the pin should be touching the insulation, no inner wire should be exposed between the pin and insulator.
3. Soldering
Sorry about the focus
We need to tin the inner, you will find the insulation will melt easily, so practice tinning wire on scraps you have around before doing this. The reason for leaving the inner insulation just proud is to allow for a small amount of shrink. When you become proficient at soldering you should be able to reduce this shrink considerably.
Now we need to add solder to the pin. Turn the pin upside down to expose the bucket, here I have stabbed it into the bottom of a tissue box to hold it while I work. Hold the iron against the bucket and allow time to heat up, when the bucket reaches a the right temperature the solder will flow, you do not put solder to the soldering iron tip, you apply it to the bucket.
Once you have solder in the bucket, hold the iron against the bucket and wait until the solder melts. Upon melting, bring in the coax and slide it in, remove the iron and allow to cool. Do not be tempted to dip in water or a wet sponge as this will weaken the joint, gentle blowing on the joint is fine.
Reassemble the components as above.
Trim the braid, but not so much that it is flush, you want to trap braid within the threads when you screw the connector front to the backing screw. Here I could have probably allowed a little more length of braid to be exposed. Important – Check for stray braid, a single wire from the braid to the pin can short your connection and damage equipment. Measure across the pin to braid with a multimeter on resistance, a dead short may indicate a problem, even with an RF antenna connected you should get a few ohms not a dead short i.e. 0 ohms.
Assemble the plug and tighten. Important – hold the back screw still with the spanner and screw on the front part, screwing the back screw at this point will tear the braid.
The finished job.
Hope it helps......
