EQUIPMENT FOR YOUR HF SHACK
Last week we discussed the essential component required to build your first HF station, the base radio or Transceiver. Tonight I’ll discuss a few other key items our HF Station list and go into a little detail on each. They will be The Power Supply, the Antenna Tuner, the Dummy Load, and the SWR Meter.
Let’s start with The Power Supply
So, for a power source, some radios have built in AC power supplies that will let you plug them into a wall socket for power, while others require a 12v power source like a 12v power supply or battery pack. Once you have your radio you’ll want to mak sure you know the max draw from your radio when transmitting at full power so that amperage is covered by your power supplies max output.
For radios with built in AC power supplies this is easy since the manufacturer took care of that for you. For 12V DC radios you’ll need to review the specs for the radio and take into consideration what other 12 volt equipment that you may wish to power simultaneously, this might include meters, and tuners.
Having purchased a few older radios I’ve noticed two patterns in 12 volt power supplies. You can either purchase a power supply from the radio manufacturer, or from a third party manufacturer. Both of the older HF radios that I’ve purchased came with used power supplies from the same manufacturer, and from the same model series of products.
For example when someone went out in years past to purchase an Icom IC-746 radio new, Icom would have had matching options like the PS-85 20 amp power supply and the SP-21 external speaker. In fact if you look up the Icom IC-746 today you’ll see that they had as many as 22 optional components and add-on’s for that radio. Optional components include power supplies, microphones, speakers, tuners, and amplifiers. Finding a used radio set that includes many of these optional extra components makes for a very nice matched set, and takes the guess work out of compatibility with your radio.
Third party power supplies from the brands like Astron, Pyramid, and MFG can range the full spectrum from ok to great if we’re considering the build quality, and remember to purchase something a little larger than your calculated requirements since often a power supply rated at say 20 amps is actually rated for 15 or 16 amps of continuous duty with 20 amps as a peak level only.
A typical 100 watt transceiver will likely need a 20 – 30amp power supply with a little room to grow your shack and enough power for continuous duty.
[QUESTIONS – BREAK]
ANTENNA TUNERS
An antenna tuner, or antenna tuning unit (ATU), is a device inside your transceiver as an option, or it’s an external component connected between your radio and its antenna. It’s designed to improve power transfer between radio and antenna by matching the impedance of the radio to the antenna's feedline. Antenna tuners are particularly important for use with multi-band antenna’s that often work on multiple HF bands, but don’t always have the lowest SWR on each and every band.
In a perfect world you don’t need a tuner if your antenna or antennas already have the lowest SWR possible, meaning they are perfectly tuned already. But since many of us don’t have the room for many antennas, we often go the route of a multi-band solution that often comes with the caveat that an antenna tuner is also required.
Transmitters feed power into a resistive load, very often 50 ohms, for which the transmitter is optimally designed for that power output, efficiency, and low distortion.
If the load seen by the transmitter departs from this due to improper tuning from high SWR of the antenna/feedline combination the power output will change, transmitted energy will be reflected back into the transmitter, distortion may occur, and the transmitter may overheat or be damaged.
Today antenna tuners are available in three basic options.
Option 1 is Automatic Antenna Tuners built into radios. This is a great radio option or feature and typically it’s the most automatic method available. Typically it’s one press of a button a few moments of work on the tuners behalf, and your good to go. However, internal tuners are often small and they won’t always tune a higher SWR into something useable, your antenna should already be fairly low SWR and this option will work fine for you.
Option 2 is an External Manual Tuner. Manual tuners are great since all the control is in the hands of the operator. Typically you’ll tune the antenna while listening to noise on a empty space on the HF band. Hearing the noise increase or decreased helps you dial in a rough tuning. Then you transmit on low power with a continuous tone and keep fine tuning your output for the lowest SWR on the antenna tuners meters. Finally you power up to your intended full output and make one more quick adjustment and you’re ready to go. You can imagine this process take a few minutes for a beginner, but with time and experience you’ll get fairly quick at it.
Option 3 is an External Auto Tuner. Brand names like LDG make fantastic auto tuners often designed for generic use with all radios, or models specifically made for certain radios. My Yaesu FT-847 came with a Yaesu matching tuner when I first bought it. Later I sold that tuner and upgrade to an LDG YT-847 that was made to perfectly match the FT-847 and offer more capability and the ability to add even more components to the radio.
[QUESTIONS – BREAK]
DUMMY LOAD
In radio this device is also known as a dummy antenna or a radio frequency termination. Is a device, usually a resistor, used in place of an antenna to aid in testing of radio transmitter. It is substituted for the antenna while adjusting the transmitter, so that no radio waves are radiated, or at least minimal radio waves are radiated. This is so the transmitter does not interfere with other radio transmitters during the adjustments or experimentation. If a transmitter is tested without a load attached to its output terminals such as an antenna or a dummy load, the power will be reflected back into the transmitter, often overheating and damaging it. Also, if a transmitter is adjusted without a load attached, it will operate differently as compared with a load, and any adjustments you make may be incorrect.
The dummy load ordinarily should be a pure resistance; the amount of resistance should be the same as the impedance of the antenna or transmission line that is used with the transmitter (which in Amateur Radio is usually 50 Ω). The radio energy that is absorbed by the dummy load is converted to just heat. A dummy load must be chosen or designed to tolerate the amount of power that can be delivered by the transmitter. Typically it consists of a resistor attached to some type of heat sink to dissipate the power from the transmitter.
The ideal dummy load provides a standing wave ratio (SWR) of 1:1 at the given impedance of 50 Ohms.
Smaller Dummy loads often just look like a medium to large heatsink with a coax connector on one end or at the back. Larger dummy loads may handle 2-3 times the legal limit in Amateur Radio transmission output and will feature SWR meters, cooling fans, and likely will require their own power source.
Veterinarian-grade mineral oil, an inexpensive source for mineral oil, is frequently used by amateur radio operators as coolant in RF dummy loads called Cantenna’s which are manufacturer repurposed metal one gallon paint cans filled with the oil. You typically purchase these types of dummy loads as the empty can with all the appropriate wiring and connections already built in, then when you get it home you fill it up.
Lots of option in Dummy Loads are available in the price range of $50 - $150 dollars.
And just a suggestion, make sure your are confident your dummy load is working correctly, before you transmit the full output power of your radio into it. Treat is like an antenna, test and verify it’s doing the job BEFORE you trust it’s going to operate as expected.
[QUESTIONS - BREAK]
SWR Meter
The SWR meter measures the standing wave ratio in a transmission line. The meter can be used to indicate the degree of mismatch between a transmission line and its load (usually an antenna or dummy load), or evaluate the effectiveness of your impedance matching efforts from a tuner or other factors.
An SWR meter does not measure the actual impedance of a load, but only the mismatch ratio. To measure the actual impedance, an antenna analyzer or other RF measuring device is required. For accurate readings, the SWR meter must be matched to the line impedance, once again in Amateur Radio that’s 50 ohms. To accommodate multiple impedances, some SWR meters have switches on the rear, to select the resistance appropriate for the sense lines.
SWR meters sometimes have two separate meters, one for power output measured in Watts and another for the SWR reflected power. More often now we see single meter designs that feature cross needle designs, that’s two needles on a single meter one rising from the right side of the display, and the other rising from the left side, as they both rise they cross each other and display the output power and the swr reflected power at the same time, all you need to do is watch both sides of the meter.
I personally have a Daiwa single display meter with the cross needle design that works on the HF bands at three different levels. Level one is 20 Watts max for doing your initial low power testing, level two at 200 watts for full transmission on my 100 watts transceiver, and level 3 which can handle up to 2000 watts or 2 kilowatts if I ever upgrade and purchase an amp.
Read up on the specs on any meter that your considering purchasing, they are made for various bands so you can purchase meters for the HF bands, or VHF, or UHF, and ranges of frequencies in between. Just keep an eye out that the meter your using must be intended for the power output and the frequency ranges that you intended to transmit on with your equipment. In the case of this discussion, the HF bands from 1.8 MHz up to 50MHz or so would be typical.
Apologies, I had intended to cover some of the discussion this evening on Coax cable as well, but I didn’t have the time to do the prep and write up the notes in time for this evenings net.
I’ll cover Coax in a future net and we’ll take the time to discuss connectors as well during that session since both topics go so well together.
So that’s our HF Station Components for this evening. Does anyone have any questions before I start to wind up the net?