KWARC Tech Corner

Locating Buried Coaxial Cable
by Greg Hollinger VE3NXB@kwarc.org

If your Amateur Radio antenna farm is anything like mine, then you probably have runs of coaxial cable from a tower or a ground-mounted vertical antenna lying buried an inch or two below the grass. When it's time to replace a run or locate a coupling--say at the end of an in-line co-axial matching stub--you may not remember where you buried the cable.

Here's what I do:
In most cases the cable shield will be connected to the antenna or tower ground system at one end and to your water supply pipe and electrical service panel ground at the other. Usually these grounds are dissimilar for medium-wave frequencies, so lots of RF current will flow through the cable shield.

Using a medium-wave (AM) battery-powered radio in one hand, sweep its loop stick antenna held horizontally and at right angles to the lay of the cable. Listen for a sudden increase in the signal strength of a distant radio station. At peak signal strength, the cable is directly under the radio's loop antenna. Now you can easily locate the entire length of cable by listening to the radio--something we all like to do anyway!--Greg Hollinger, VE3NXB, 270A Northlake Dr, Waterloo, ON N2V 1A9, Canada; e-mail ve3nxb@kwarc.org

Dr. Solder (an excerpt)
by Larry Smith Weller engineering support
Contributed by Ron Hands VE3SP, Hamilton

A: A non-temp controlled iron *continues* to increase in tip temperature the longer it's plugged in -- up to 1100 degrees-F ! A solder station controls and maintains an exact tip temperature. In the case of 700 degree-F tips, you'll be soldering at a tip temperature of 400 degrees *less* than a non-temp controlled iron. A lower tip temperature with good technique, translates to better joints with less chance of damage to sensitive components -- IC's, etc. (The 700 degree-F Weller tips will *not* exceed 710 degrees-F.)

A: The 700 degree-F tips are typically recommended for single layer and double-sided PC boards -- even four-layer PC boards. This includes practically everything in the world of amateur radio kits & homebrew. The most common tip for the WTCPT station is the Weller PTA-7 (1/16" screwdriver tip). You might also want a PTD-7 for much bigger pads/lugs, and a PTJ-7 for longer-reach work – or gasp rework ;) If you want to try surface mount, pick up a PTS-7 for a start. The 800 degree-F tips are recommended for serious multi-layer boards -- 4 to 8 layer PC boards -- *not* typically used for ham radio kits ;)

A: Tricky question! The time spent on the pad is called "dwell time." A dwell time of 4 seconds at 700 degrees-F might be considered destructive for some components -- however, a dwell time of 2 seconds with an 1100 degree-F unregulated soldering iron can be much more destructive. A 700 degree-F dwell time of 3-4 seconds is not uncommon, to allow for "filling the pocket" -- that's the volume of the thru-plated hole, flush to the component side and properly "feathered" evenly to the circumference of the solder pad -- on the solder side. The "pocket" should be filled -- but not over-filled -- and the solder in the center of the pad should rise evenly to the component lead that will be trimmed. Never have a solder pad with an under-filled "dimple" on the pad. The solder level at the component lead should be higher than the edges of the pad. A soldered pad should never look like a "round BLOB of solder *sitting* on the pad." Wire soldering is more of an art than a science, and with practice -- 1 to 3 second dwell times can be achieved, while safely meeting all of the above criteria.