For many decades there was only one choice. Power supplies had heavy iron transformers to convert house current (110/120 volts AC) to the lower voltage required by many solid-state devices. As the demand for more and more current increased so did the weight of the transformer and the complexity of the circuitry making the DC. These are referred to as linear power supplies.

Then a strange thing happened: The heavy transformer went away. Switching power supplies (also called switch-mode power supplies or SMPS) arrived and changed how DC was made. Without the heavy transformer (solid-state devices are used) power supplies could be made smaller and lighter while providing the same output current.

So… which method is best?

The answer to that question depends on your intended application. In applications where size and weight are major considerations the switching supply wins, hands down. Because large iron-core transformers are also expensive, switching supplies can be less expensive than linear supplies. Size weight and cost are three BIG advantages!

In applications requiring a low-noise highly regulated DC output, such as laboratory equipment, sensitive radio receivers, test equipment and bio-medical equipment, linear power supplies still have a slight edge. The requirement for completely noise free output overrides the advantages of the switching power supply in certain circumstances.

Noise?

Switching power supplies use high frequency switching transistors to make the output current. The generation of high-amplitude, high-frequency energy requires that a low-pass filter must block the high frequency noise at the output to avoid electromagnetic interference (EMI) and ripple voltage at the switching frequency and its harmonics. Very complex filtering developments have almost completely eliminated this problem. Very low cost SMPSs may couple electrical switching noise back onto the AC power line, causing interference with Audio/Video equipment and any other electronic equipment connected to the same AC phase. This is still a major problem in poorly designed, cheaply made SMPS units flooding into the US market from overseas.

What’s the bottom line?

Dollar for dollar switching power supplies usually provide more power for less cost. They are also smaller and lighter than standard iron-transformer linear power supplies. In applications where switching noise is not an issue, they are clear winners. Most switching power supplies sold for Amateur Radio use by reputable companies are noise free. Where size, weight and cost are secondary to high-quality low-noise DC output, linear supplies still have an edge.

Understand the requirements for your application and read the specifications for the available power supply types that meet your need. Then make your choice carefully, keeping your application solidly in mind.

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Choosing the right coax may seem complicated given the wide variety of cable types, their specs and costs. When we talk about coaxial cable loss, keep in mind that it affects transmitted energy as well as received signals. At 38 cents per foot, RG-8X is attractive, especially when putting up a new antenna system.   However, at 150 MHz, 100 feet of RG-8X has 3.8db of loss. So on the 2 meter band with 50 watts transceiver output, you would lose more than half of your transmitted power! Your station’s receive performance would suffer as well.

DX Engineering 400MAX is a better choice for VHF base applications. At 150 MHz, the loss of  100 feet of 400MAX is only 1.8db. RG-8X is fine to use for short coax jumpers and in mobile applications. You have probably noticed that most mobile mounts use either an RG-58 or RG-8X.  That is because at such a short run the loss is negligible. For HF base applications RG-8X is a popular choice with only 0.9 dB of loss at 10 MHz and 1.4db at 30 MHz for every 100 feet. It is certainly acceptable to use higher quality low loss cable on the HF bands. Many amateurs choose DX Engineering 213 or 400MAX because both are suitable for direct bury applications.

Feel free to contact DX Engineering anytime you have questions about the right cable for your application.


Combination SWR Meters (sometimes called SWR Bridges) and RF Power meters (also called watt meters) are useful accessories in the ham shack. They provide information about transmitted and reflected power, and Standing Wave Ratio (SWR). Prices can range from about $80 for utility meters to over $500 for commercial grade meters.

Selection Criteria:

Maximum power you will likely be using: Meter reading accuracy is best when the power reading is over half scale. Some meters are for low power only (20 watts) others high power (2,000 watts) and some meters have switch selectable ranges (20 / 200 / 2,000 watts)

Frequencies you will be measuring: Be sure to select a meter designed for the frequency ranges you will be measuring. Some meters are designed for HF and VHF frequencies, others for VHF and UHF frequencies

Ease of viewing: Meters with larger faces are easier to view. Some meters have lighted meter surface for improved viewing in low light environments (typically requiring a 12V DC power source for the lamp)

Single or Cross-Needle Display: Most users find the cross needle variety more convenient. One needle measures forward power, the other needle measures reverse power, and a graph on the face of the meter beneath the point where the two needles cross reads the SWR.

A single needle meter has a switch to select forward or reverse power display.

Accuracy Requirements: Inexpensive SWR / Watt meters are accurate enough for general amateur use, typically better than +- 10%. Where a greater degree of accuracy is needed, a commercial grade directional wattmeter is needed at a significantly higher cost.


Most amateur radio operators (hams) know they should weatherproof any coaxial cable connections that are outdoors to prevent moisture entering your coax connectors.

However, many hams don’t realize you must also protect lightning protectors if they are mounted where rain, snow or other foul weather may be present.

One of the most popular brands of lightning protectors that have been around for years is PolyPhaser. In their instructions (who reads instructions?), PolyPhaser warns that the lightning protector are NOT weatherproof and need protection. Most other brands are also not weatherproof.

If you don’t weatherproof the lightning protectors, moisture can get inside and ruin the protection and possibly do damage to your transceiver by reflecting too much RF.

Not all products are equal. Some can make disassembly difficult, others can make it easy. At DX Engineering, there are a number of products that can be used to weatherproof your lightning protectors, yet still make them easy to service.

The recommended way to weatherproof a lightning protector, once it is mounted and the coaxial cables are connected, is to completely encase the protector and coax connections with Scotch 33 or Scotch Super 88 tape. Once the tape is in place, use Self-Adhesive moisture sealant pads, tape or Temflex Rubber Tape to again, completely encase the protector and coaxial cable connections. But wait, there’s more – One more layer of the Scotch 33 or Scotch Super 88 and then job is complete.

Someone just asked – ‘Why the first layer of tape?’  Ahhh – that’s what makes getting all that sticky stuff off without having problems with residue left on the lightning protector or coaxial cable connections.

Remember – Three Layers: Tape, Sealing material and then Tape. This winning combination will you keep your station in top operating condition.

Recommended DX Engineering products:

TES-06132      Scotch 33 tape

TES-06143      Scotch 88 tape

TES-06147      Scotch Moisture Sealant Tape

TES-06149      Scotch Moisture Sealant Pads

TES-2155        Scotch Temflex Rubber Splicing Tape

DXE-WK-2    Scotch 33 tape and one 3” x 6” Self Adhesive Weatherproofing material

DXE-WK-3    Scotch Super 88 tape and one 3” x 6” Self Adhesive Weatherproofing material


“Wow! I just got another transceiver. I’m gonna need a coax switch. I’ll get a used switch off the web.”

Bad idea… Used coax (coaxial) switches come in all conditions. A few will be like new. Others will have burned contacts from surges and arcing, corrosion that can’t be easily removed, worn silver on the switch contacts, slop in the switch mechanism and many other ills. Why would you want to connect your high-quality transceiver through a junk switch that could present a high SWR, or worse?

Quality coax switches have high isolation (typically in excess of 50 dB), low RF resistance (insertion loss), low VSWR and firm, crisp switching. Isolation is very important when switching two or more rigs to the same antenna. RF leakage from one switch port to the other can overload and even damage other radios in the system. As long as the ports are well isolated from each other, that problem is controlled.

Insertion loss reduces your received signal and creates heat (resistive loss) in your transmitted signal. Normally, a few tenths of a dB is easily tolerated. As frequency increases, insertion loss usually does, too. A switch with 0.2 dB insertion loss at 3.5 MHz may be well over 1 dB on two meters! It’s important to look at the full specs.

Switch SWR is also important. We all want our antennas to operate at maximum efficiency. That usually means watching our SWR. A good switch will have an SWR of less than 1.2:1. This rating goes back to insertion loss; the lower the SWR the lower the insertion loss will be, and vice versa. Again, SWR normally increases with frequency.

Mechanical design is also very important. You want the switch to feel solid and to have crisp motion when the switch is used. Avoid lightweight switches with sloppy switch mechanisms. Robust mechanical feel is usually a good indicator of internal construction.

Coax switches have limitations on maximum RF frequency and power. DON’T rely on engineering fudge factors here. Exceeding these ratings can cause outright switch failure and damage to your gear!

 


Tinned-copper braid has been around for a long, long time. It’s been used in many grounding applications because of its flexibility and ease of soldering. It’s great for grounding radio chassis to radio chassis (DXE-TCB05-RT01) or from your equipment to a single-point ground. Good stuff. (DXE-TCB-050)

Copper strap is better than wire because it reduces RF skin effect with the very large surface area it presents.

There is a problem with braid: it retains water. The fact that it will hold water causes corrosion to the tinning material and, eventually, the copper. This may not be a problem in New Mexico but it is in many parts of the US and the World. Tinned-copper corrosion is evident when the braid begins to turn green.

That’s where copper strap comes in! For grounding connections that go outside the building and into the weather, the better choice is copper strap. Copper strap (GCL-1220-025) dries quickly, its oxidation actually protects the strap, and it will far outlast copper braid when used for the same outdoor application. Copper strap also reduces RF skin-effect resistance over the use of wire.

So, which is best? Both! Use convenient and flexible braid in the shack to accomplish your equipment grounding needs. Then transition to copper strap to go outside the shack and into the weather.

 


Q: If RF is a high frequency AC signal, why are there plus and minus signs on a balun?

A: Keep in mind that we are usually connecting a ‘BALanced’ antenna to the ‘UN-balanced’ coaxial cable, hence the term BALUN. So, for most regular applications on a single antenna that is ground independent, such as a beam, dipole and many other wire antennas, the balun polarity doesn’t matter. However, polarity markings on baluns become very important for matching phase on multiple antennas in a phased array, such as stacked Yagis. Also, on most 1:1 baluns, the minus side is connected to the coax shield. So, for an antenna that is ground dependent, such as a vertical, Inverted-L or long wire that uses a ground radial system, the positive terminal must be connected to the radiating element and the negative terminal must be connected to the radial system.