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Old 07-21-2009, 05:07 PM
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RicardoJM RicardoJM is offline
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Default Solder Guru

The bottom coax connection of my home brew 2 meter antenna came loose. Yesterday evening I went to repair it and found my soldering skills were not up to snuff. I'm using a 25 watt Weller iron. In particular the connection from the center of the coax to the copper wire (4th row of the coil) does not hold at all. I'm not able to get a good tin on the copper wire and my connection peels off with the slightest of effort.

Is there a solder expert that could lend me a hand with getting this done well so that I can the antenna back into my truck? I'm on the south side of town, but will travel if needed.
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Old 07-21-2009, 05:28 PM
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I am not Dave, but cleanliness is next to nirvana in soldering. I have to solder steel and aluminum to copper all the time. you will need to acid flux and use pure silver solder, imho, but please wait for dave. on large gauge wire/coil, I use a mapp torch exclusively.
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Old 07-21-2009, 06:15 PM
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Bruce Miller Bruce Miller is offline
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All copper to be soldered must be clean and bright. On the coil part, gently pry a screwdriver between the round plastic and the copper coil to give you space to brighten the copper with a small strip of sandpaper or emery cloth. Once all the copper is clean and bright you're ready to solder. A 25 watt soldering gun or iron is too small. Don't try to use it as a joint soldered with it may appear to be good buy I would have my doubts. You need more heat, probably up to a 75 watt iron, minimum.

Bright copper and more heat and you should be back in business.
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Old 07-22-2009, 08:36 AM
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RicardoJM RicardoJM is offline
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Yup, I understand about the clean thing. I think Bruce is right on about the iron not being up to the job for getting a good connection on this part of the antenna. I held my iron on the copper coil for several minutes and it would not get things warm enough to tin. In frustration I resorted to scraping the solder onto the copper coil, but it was not a solid connection. I went through several rounds of cleaning up the copper, heat the coil wire, scrap on the solder - followed testing the connection and seeing it fail. I used the same iron when making the original connections during the antenna building party.

The original connection was just a frail as my attempts a couple of nights ago. That said, this connection did not fail. When I removed the shrink wrap for this repair, the connection was still good - although it did not take much to get it to separate. This is what prompted me to pay closer attention to this connection on this go around.

For others running the home brew antenna, I'll share some insight on where my antenna failed. The failure point was in the copper braid that we attach to the bottom of the antenna. This copper braid is what we made in step #7 of Jeff's post. In my failure, the copper braid severed. I am speculating that all the bouncing around put stress on each small wires in the braid causing them to snap - one at a time until they were all severed. The solder connection to the bottom of the antenna was still good. This time around I tinned the exposed copper wires of the braid and expect that the solder will give it more strength. Time will tell, but I am not expecting to see the same failure.

Regarding the original challenge, upon noodling on it a bit I took a different approach to making a solid connection with the tools I have. I stripped the sheathing from a bit of 14 gauge wire making all of the small strands of wire available. I then took 4 of the small strands and braided them into a strap. I used the strap to lash the center wire of the coax to the 4th row of the copper coil. This resulted in a solid connection. I then soldered the strap to the center wire of the coax. Between the strap holding the the connection together and a good solder connection between the strap and the coax center wire I feel the connection is stronger than the original. Of course, the shrink wrap further secures the connection. Being that the original frail connection had not failed and this new connection is stronger I feel good.

I don't have an SWR meter and have not taken a reading. I did give it a try and was full quieting on the 146.940 repeater with 5 watts.
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Old 07-22-2009, 11:20 AM
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My NASA soldering instructor would shudder.


Don't try to launch that thing, not to flight specs.
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Old 07-23-2009, 08:22 AM
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I should be around this weekend, if you want to give it the once over either here at work or at my house, I don't mind. My soldering iron at home is Hakko 936, it'll toast about 60W and I have a couple of fat chisel and bevel tips for it that should work. If not, I do have a 100W Weller that doubles as Kirsten's stained glass iron, that'll melt lead cane...

Soldering, the bigger the blob the better the job. Yeah, not so much. I am not NASA qualified (they wisely do not let us engineers touch an iron to flight hardware), but I was IPC soldering trained at HP. That was 13 years ago that I was a bench tech and I'm no where near as good anymore.

Keys to soldering, clean surfaces, enough flux, the right heat and time. It's really pretty easy if you have the right iron and solder. Oh and now a good scope, mine eyes are starting to let me down. I suppose it's too often trying to rework 0402 parts without optical help is starting to catch up.
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