Tuesday, October 30, 2018

A simple coax switch...

Sooner or later every ham station will need a way to switch coax connections. There are plenty of commercial switches out there, MFJ offers a decent one that is easy to find. And you can always spend an afternoon collecting the parts and assembling your own. However, both options wind up being a little expensive when all you need is a switch to temporarily evaluate a new radio or some array of antennas.

Wanting another switch, I searched ebay and ran across a 3 position switch made by Workman. It claims 1000W, which I didn’t believe but it was only $12, something I could afford to lose when packing up after a field day. I remember the Workman brand from the 1970's. They mostly had tools and accessories for the TV repairman but also a few reasonably priced items for the hobbyist. I bought three of the switches and they arrived in the predicted 8 days by China post.

As a test the switch, was put in place between my radio and a 20m dipole on position 1 and a 40m dipole on position 2. Sadly, there was a noticeable decrease in signal and without re-tuning, the SWR was also worse. The MFJ switch didn’t exhibit either problem.

So, what's up? It is just a stupid switch. Popped the back cover (two screws) and surprise, it is packed with wires!! WTF! You would expect one wire from each connector to the switch and not much else. It is a cheap switch so you would expect the grounding rely on the screws to the case.

A little closer look and it seems that someone decided that the grounds should also be switched. It makes no sense because they are all tied together anyway! Whoever sent the order to the manufacturer probably wasn’t all too clear on the actual requirements. The good news is that the switch itself is a reasonably good one, and the SO-259 connectors look fine.

Ok fine. Grab a soldering iron and pull out all of the wires other than the four wires from the center of each connector. And even those were un-soldered from the switch.

That's better, now put the four wires back on the switch (on this particular switch I elected to put the input on the side with 3 connectors, your choice). Keep the lengths as short as practical.

Now the grounds. An ohmmeter suggests that the connections are pretty good between the case and the connectors but it looks more accidental than intentional. So, we could use some of that left over wire to tie each connector shell together, or try something better. I happened to have a bit of copper foil so it took a few minutes with a large soldering gun to tack it to each connector and to the steel box after scratching off the paint (good paint BTW). Some bits of copper clad PC board will also work

In this case I had to re-label some the switch positions, but otherwise it looks like the original. A quick test and it now behaves as well as the MFJ version at least under the above conditions. I didn't bother to test it on 2m, but it is probably only useful for HF.

Conclusion: You cant beat this as an option for an occasional use switch. The parts are worth more than the purchase price and it takes barely 20 minutes to do the rework. In spite of the nice statement on the label, this is not the switch to use if you are running more than a couple hundred watts, but it is great for field days and they make welcome gifts for your ham buddies.

1 comment:

  1. stainless steel knurled steel - TitaniumFarms.com
    Stainless steel knurled titanium quartz steel knurled steel used as a base for blades and blade blades. titanium knee replacement These stainless steel knurled knurled steel nipple piercing jewelry titanium give titanium 6al4v you  Rating: 5 · ‎5 reviews · ‎$5.25 · titanium coating ‎In stock