The Alpha Delta 2B and 4B are the most common affordable antenna switches for amateur radio use. These switches are prone to a few problems. The first problem shows up on even brand new switches. The Alpha Delta switches are a big upgrade over the newer MFJ or the older Heathkit antenna switches. The MJF and Heath switches eventually develop wear on the standard rotary switch wafer contacts, exposing the base brass by wearing away the silver plating. I was suprised when I opened up my Alpha Delta switch. I did not find self wiping silver or gold plated contact buttons. The switch contacts are just the phosphor bronze strap, a springy material. They are silver plated, and when they are properly adjusted, the contact surface is large. Also, the casting that forms the enclosure provides a strip line for 50 ohms, and good isolation between ports. A lot of manufacturers use silver contacts. If you do not use your station for weeks at a time, ANY silver plated contacts, whether on relays or rotary switches WILL develop intermittent contacts. Sometimes, you can just operate the relay or switch a few times, and the problem clears. The internal antenna tuner in my HF radio sometimes does that, when my "to do" list overwhelms me and I do not get to play radio as often as I would like. The (in)famous Dow Key T/R relays are notorious for that problem.
In fairness, the Alpha Delta switches give good value in the $100 price class. You have to go to $500 to get something better from Bird. But the Bird is only rated at 850 watts to 100 MHz. The common connector attaches to a very flexible piece of coax that may wear out eventually. Doesn't everything wear out in some way, though? But this comparison is given to show the good value delivered by Alpha Delta. Jetstream, Comet, Diamond, and MJF make switches similar in appearance. I found a picture of MFJ antenna switch internals. A link for comparison is posted at the end of the article. Anyway, this article is how to get your Alpha Delta working properly again. Check out the reviews for both Bird and Alpha Delta below:
FOUR COMMON PROBLEMS WITH ALPHA DELTA 2B AND 4B ANTENNA SWITCHES
- While the Alpha Delta antenna switches are rated at 1500 Watts, the paper sticker on the back states the D-4 arc plug will fire if the SWR exceeds 2:1 at full legal limit. Further, the advertising states: "These switches feature a built-in surge protector. A replaceable D-4 Arc-Plug cartridge will divert harmful surges to ground. (Note: The Delta switches reduce the hazard of lightning induced surges. They will not prevent fire or damage caused by a direct strike)." That is pretty good truth and honesty in advertising. I recommend REAL protection outside the house, by disconnecting all feedlines and grounding them a good distance from the actual home, in the event of dangerous storms or vacation away from home. I also recommend removing the arc plug if you are running over 400 watts PEP, especially with a standard 80 meter dipole or a shortened vertical, for instance. Its SWR at the band edges can easily exceed 5:1, if cut for center band. Simply unscrew the brass plug near the common port. Remove the arc plug by tapping the switch while holding it upside down, and it will fall out. Store the arc plug, in case you need later. Frankly, I wish I could have bought a less expensive version WITHOUT the arc plug feature, but otherwise the same.
- The Alpha Delta 2B and 4B antenna switches are supposed to ground all unused ports. When the switch knob is pointed at the "common" connector, the "common" coax connector is NOT grounded. This information may be useful if you are doing something other than the usual application with the switch. Sometimes, the grounding contact gets dirty or out of adjustment and fails to operate. This is why you should NOT use this style of switch to select between high power stations, especially when using solid state receivers or transmitters. The isolation when operating as designed is specified at 60 DB below 30 MHz. When running multiple full legal limit stations, I prefer to use a patch panel with jumper coaxes to avoid taking a chance with this feature. When selecting antennas, this failure mode is more of an annoyance than a problem. There are Alpha Delta switch models 2B/N and 4B/N for UHF; their only difference is the connector furnished. There is no difference in internal construction or contact material.
- The Alpha Delta 2B and 4B antenna switches should provide a low resistance contact to the intended port from the common port. Silver-plated phosphor bronze micro strip construction ensures loss of less than 0.1 dB at 30 MHz. Sometimes this contact gets dirty or out of adjustment, resulting in higher than expected SWR. You can check this problem or the grounding issue with a standard Ohm meter with a good low range.
- Both problem 2 and problem 3 can be remedied by cleaning the contact with a Q tip soaked in Isopropyl Alcohol. DO NOT USE ABRASIVES OR GREASY CONTACT CLEANERS! Make sure no fuzz from the Q tip is left behind. Check adjustment by operating the knob and testing with an Ohm meter afterward. Yes, the detents are sloppy feeling when the switch is disassembled, since the roller is not in contact with the bumps on the bottom plate you previously removed. Reassemble the switch after cleaning and check the contact resistance again before putting it back in service.
HOW TO GET THE ALPHA DELTA 2B OR 4B ANTENNA SWITCH APART TO CLEAN AND ADJUST IT:
- Disconnect it from your radio system and look at the back. Remember the information on the label, or photocopy it or scan it on a flat bed scanner, if you want to replace it. Remove the label.
- There are two phillips head screws under the paper label. Remove those 2 screws, as well as the others that were not hidden.
- Carefully remove the bottom plate, being careful not to damage the switch shaft that passes through the bottom plate.
- Inspect the contact surfaces as you operate the switch. Clean them with alcohol only as noted above.
Small careful adjustments can be made to the center contact strip, if cleaning does not correct the problem.
- Reassemble it and test it with an ohm meter before putting the Alpha Delta antenna switch back in service.
Link to MFJ knock off antenna switch internal view, for comparison. Note there are no shields between the ports, maybe OK for HF port to port isolation, but not above 30 MHz:
The photos above show what is inside the Alpha Delta 4B switch, and how to take it apart. Click on the photo to enlarge it. I hope this article helped you solve your Alpha Delta 2B or 4B antenna switch problem.