Tired of chasing your key around the operating desk? Miniature keys are the most problematic. Some of mine are so tiny that there isn't enough room to hold them down and key them at the same time. Permanent magnets are a good solution.
I like the rare-earth type super-magnets. Especially the little ones sold to crafters for hidden lid closures and such. The tiny buttons can be glued to the bottom of the key and are thin enough to allow placement of those little soft “rubber” feet under there as well. The feet are tall enough that the magnets never quite reach the surface below but are close enough to provide a herculean pull. In the field I can stick a key on the radio cabinet or any convenient steel surface and not worry about scratching it up. On the operating desk I use a small piece of 1/8” steel rack panel 6” by 8” with low profile feet on the underside. I then stick my little novelty keys on that.
I found a great deal on a soldering iron at a recent swap meet: A Weller® WTCPS only missing the holder for the iron. Somebody else was parting with an old Archer® soldering iron holder for cheap. Serendipity! A light touch with a file and the iron slipped right in, comfortably at home. Evidently the holder was designed for someone that didn't constantly bounce about the lab. You needed a good sense of balance to keep it upright with the hot iron in it. Upon inspection I found a thin metal plate underneath but it was light weight. A set of magnets retrieved from scrap hard drives eagerly snapped to position beneath that base plate where the rubber feet would just keep them clear of the bench top. My soldering workbench is an ancient metal-topped dining room table. Quite impervious to solder splashes, dropped tools, and other careless errors. It fits my delicate (OK, bull-in-a-china-shop) work style. Moreover, it is painted steel! That soldering iron holder now has to be pried off the bench to move it.
No glue. No screws. No commitments.
Since these critters are primarily electromagnets operating switches often we can modify relay characteristics by placing a permanent magnet nearby. Reed relays are particularly easy to affect. By carefully and precisely positioning a magnet we can provide a permanent bias to adjust the initial “turn-on” voltage and the “off” voltage points. Most relays are sealed and impossible to adjust otherwise. Using a magnet glued to the relay case, or nearby, might help avoid replacing it with a different type. Save power by using a normally higher voltage coil at lower voltage. If a reed relay has its contact bars slightly magnetized then you might be able to bias it sufficiently to make it work as a polarized latching relay. This takes patience. Even then, it's not possible with many relays. When you get the right magnet in just the right place then the relay will operate and stay active after you remove the drive current. The only way to turn it off is then to apply current to the coil in the opposite polarity. Nice for antenna tuners and such, since power needs to be just a pulse rather than a continual holding current. Various shapes of ceramic magnets work well here. The larger area and weaker field can be advantageous. I'm not talking about those plastic magnets that you stick on the 'fridge. Those are much too weak.
If you haven't heard of an isolator then you are not alone. These little guys are used mostly at VHF and above. Based on ferrite circulators, a common microwave feed line combiner and directional coupler, circulators are a passive element with at least three ports. Signals into the first port appear at the second with low loss. Signals coming into the second port from the outside world don't appear at the first port, though. Instead, they appear at the third port. And signals into the third port don't show up at the second port: They go to the first port! See? It's directional. The signals circulate from port to port in one direction only. This is handy for combining transmitters to a common transmission line since it keeps each transmitter from seeing the others: You want them just looking at the antenna, not feeding the output stage of other transmitters. Now, if you put a dummy load on that port #3 then you made that circulator into an isolator. Signal from the transmitter is passed toward the antenna but reflected signal from the antenna just goes to port #3 where it is swallowed by the dummy load. The transmitter always sees a nice perfect load impedance no matter what indiscretions occur in the antenna system. As if that wasn't sweet enough, any signals coming from the antenna (neighboring transmitters in particular) don't go into the transmitter finals where they would mix up some intermodulation products. Yes, final amplifiers make great mixers. We Pixie operators know that.
OK, back to our story...
Circulators and isolators are expensive. There are lots of surplus units, though, for little to nuthin'. Trouble is, they are frequency selective and won't work on the ham bands. Pick up one and read the label. Says to avoid magnetic fields. Ahaa! The ferrite structure is tuned by an internal permanent magnet. I picked one up that was surplussed from IMTS service just above 150 MHz, glued an alnico magnet in a sweet spot on the side of it where it tuned it down to our 2 meter repeater output. Works like a champ.
Feeling Lost?
Any time you include magnets in your equipment don't forget that they are there. If you use a compass to navigate then drop your backpack and walk well away from your equipment before taking a reading. Magnetic fields decrease rapidly, diminishing at the cube of the distance compared to the square of the distance that we are familiar with radiation field strength, but remember that they are there. Attaching a key with a magnet to your radio just might tune you to another frequency. Permeability Tuned Oscillators are especially affected. Anything with a core is suspect. No big deal. Just keep it in mind and try it out before it becomes important. My friend Clark (WA3JPG), who proof-read this for me, relates attaching a key magnetically to his FT817 only to have it wildly shifting frequencies until he realized the cause. See? It can happen to anyone. If you really insist on attaching a key to the rig then consider gluing a thick piece of mu-metal (a high-permeability alloy) on which to attach the key magnets. Old computer hard drives contained those extreme magnetic fields just millimeters from the sensitive magnetic media platters. There may be a lesson there!
de ND6T