Date: Wed, 25 Sep 1996 10:45:04 -0700 (PDT) From: Doug Hendricks To: qrp-l@Lehigh.EDU Subject: [448] Soldering RG174 Jumpers the K4DRD Way Message-ID: <1.5.4.16.19960925100738.25ef449c@telis.org> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" When I built my Sierra it took me 5 tries before I was successful in getting the W1 and W2 jumpers made from RG174 soldered in without a short. The recent posting about the problem has prompted me to share this with the list. Stan Cooper, K4DRD is a master craftsman when it comes to building QRP Rigs. An example of his work is the homebrew front panel cutout for his Sierra on the front cover of the April issue of QQ. Stan helped me to install the KC-2 in my Sierra, and I watched as he demonstrated his method of soldering a RG174 jumper. Here it is. The problem with using RG174 as a jumper is that when you solder the braid you will apply too much heat and cause it to melt right through the center insulation material and short out to the center conductor. The probem is intensified if there is any strain on the shield which is usually present when the center conductor is soldered in first. Stip the insulation back 3/4" from the shield. Then, untwist the shield so that you can retwist it into a lead separate from the center conductor. Then, cut off the twisted shield so that you leave a piece about 1/4" long. Use a resistor lead that has been cut off, and insert it into the end of the shield. Next, place an alligator clip on the shield to act as a heat sink. This will keep the heat from traveling up the shield and melting the insulation around the center conductor. Now, solder the resistor lead to the shield, doing it as quickly as possible and using as fine a tipped soldering iron that you have. Cover with heat shrink. Strip the center insulation back about 1/4" from the center conductor. Twist and solder coat the lead. Prepare the other end of the cable the same way at this time. Now, insert the resistor lead that is connected to the shield into the pad and solder. It is important to solder the shield first, to keep the stress off the center conductor. Next, solder the center conductor. Then, check the other end of the RG174 for shorts. There should not be a problem if you use a small iron (15-25W) and keep the contact of the iron to the shield to a minimum. It also helps if you allow time for the joint to cool before you start soldering the next joint. Stan, thank you for showing me a neat way to do a difficult job. I was amazed at how simple it was to do the above operation. I had a horrible time trying to work with the jumpers in my Sierra, and Stan, the master craftsman, showed me how easy it was to do. That brings up another point. Take advantage of the opportunities to watch someone else build. I have learned many shortcuts and easy to use tricks with this method. Learning is fun. (That is my business by the way!!) 72, Doug, KI6DS ------------------------------ Date: Wed, 25 Sep 1996 16:03:55 -0300 From: Ed Tanton N4XY To: ki6ds@dpol.k12.ca.us Cc: qrp-l@Lehigh.EDU Subject: [451] Re: Soldering RG174 Jumpers the K4DRD Way Message-ID: <3249821B.6A40@avana.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Doug... Another alternative on mini-RF (or audio) cables is to watch the surplus market (mail order and hamfest) for teflon cables. Usually they are even silver plated mil-spec and will not short when soldered no matter how hot your iron. I threw away ALL other kinds of mini shielded cable(s) years ago after a similar bad experience-and that was after being as quick and careful as I could be...still a short with regular '174. I have bought small lengths wherever I could ever since of the teflon kind and have never once had a problem with cable melt. There are connectors available from Digikey that will allow you to properly terminate a cable with an attached ground wire. These are beautiful but @ $1+ per connector somewhat expensive. If anyone wants the part numbers I'll be glad to provide them. -- Ed Tanton N4XY (770) 971-0436 Marietta, GA email: n4xy@avana.net URL: Coming Soon ------------------------------ Date: Wed, 25 Sep 1996 13:45:59 -0700 (PDT) From: "David D. Meacham" To: Doug Hendricks Cc: Low Power Amateur Radio Discussion Subject: [454] Re: Soldering RG174 Jumpers the K4DRD Way Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Doug/Gang, Another frequent problem encountered when using RG-174 is that a single piece of braid wire (very small diameter) gets bent or broken in such a position as to short to the center-conductor joint. This type of short is very hard to detect unless you use some sort of magnifying lens to inspect your cable ends. Another "trick" comes to mind for those cases when you want to "float" the braid at one end of the cable to avoid a ground loop (the Cascade is an example). Just trim the braid very close to the end of the jacket, using nail scissors. Then use heat-shrink tubing to cover some of the jacket and a tiny bit of the dielectric (shrink it on with heat from a butane-lighter flame). The dielectric should extend beyond the shrunken tubing about 3/16-inch, and the tinned, twisted center conductor exposed beyond that. At this point you are ready to solder the center conductor into the PCB pad. 72, Dave, W6EMD ------------------------------