High Frequency Ops: A Dedicated QRP Rig vs. Full Power in the Field

High Frequency, or HF, is the method used to communicate over long distances with no infrastructure other than you, your radio, and an antenna. HF signals travel beyond Line of Sight (LOS) where Very High Frequency (VHF) and Ultra High Frequency (UHF) quit working. For a lot of people just getting into the communications arena of preparedness or looking to upgrade their capabilities for regional networking, the most common question that comes my way is justifying the cost of equipment. Usually this revolves around two very different areas- QRP, meaning low power but generally ~5W and QRO, or ~100W rigs. Since the communications in the field is not a one-size-fits-all affair, there’s very different considerations from what an operator expects in a base station to what can be run for a long period of time out of a pack. It’s not only important to know the difference in Signal Strength between the QRP and QRO but to know the basics about the rig itself, specifically power efficiency, and what affects that strength. Each have a purpose, and with knowledge and experience a good field operator can make the same contacts running much less power than many would consider possible. While running a rig in the field for a EMCOMM, summer or winter Field Day, National Parks On The Air (NPOTA), or Summits On The Air (SOTA) activation, power consumption and antenna efficiency can become the difference between having a successful day or a big waste of time and may mean the difference between passing critical information or becoming part of the problem. Selecting a field rig is a bit different animal from what you’d run in a base station or mobile rig, and there’s a few pointers we’re going to cover to make the selection a bit easier for your needs.

QRO: 100W and a Wire

The first rig you should buy when getting into HF is a QRO, or ~100w transceiver. Why? Because having a higher amount of power available to you can compensate for a less efficient antenna system, poor or dynamic solar conditions, and operator inexperience. Yeah, QRP looks cool but you gotta start somewhere. Making contacts is the important part. With 100w you can always decrease power but having that extra output may make the difference between a solid but readable contact or simply fading into the noise floor. With the generally bad solar conditions we’re currently experiencing on HF, having that extra power in a base of operations comes in handy.

But running a full-powered rig in the field becomes tricky. While it’s possible, and I’ve done it more than a few times, a QRO radio is power hungry and requires large capacity batteries for extended operations. If you’re only out for a short trip, such as a SOTA activation or an afternoon in a park, the needed batteries aren’t that big of an issue. There’s many compact HF rigs that offer 100w also, including the very popular FT-857 among Preppers, so size or weight is not exactly a problem in a pack. But the current draw, 1.2A on receive, is a problem if you’re working out of that same pack for more than a day. 1.2A on receive becomes 4A of consumption for 5w of transmitted power out of that same 857. 5A for 10w, 8A at 25w, and 21A at 100w. So if we’re working with an inexpensive Sealed Lead Acid (SLA) Battery, commonly in a 7 Amp-Hour (Ah) size, our 4A for 5W only gets us 1.75 hours of transmitting time. So while 100w in the field is nice, the power consumption tradeoff forces us to look elsewhere.

Enter QRP

Low powered rigs can be every bit as polarizing among hams as a caliber debate among gun nuts. “Life’s just too short for QRP!” Which is every bit as equivalent a statement to “the only useful calibers begin with a 4 and end with a 5!” or “.223 is a poodle shooter!”. A lot of huff with little fact and in both cases shouted by a curmudgeon. If you’re planning on working off-grid for an extended period of time, power consumption rapidly becomes a QRP operator’s most important number.

Compared to our FT-857 example from above, a dedicated QRP rig really begins to shine with its efficient use of power. The ubiquitous FT-817 consumes a mere 450mA on receive with the backlight on and squelch off, and around 300mA with the light off, squelch up and volume down. On transmit it consumes 2A for 5w output, being twice as efficient at the same power level as the FT-857 with a smaller footprint. Other rigs have similar numbers, like the excellent Icom 703’s 300mA and 3A at 10w or the ideal Elecraft KX2’s 150mA and 2A at 10w.

Aside from power consumption, a QRP rig will allow you t get more use out of your battery.  By design, most are able to run at lower supply voltage. For a 100w rig, almost all of them will stop running at 11v. If they still power up, the audio will sound garbled and those of us who’ve experienced this call it ‘motorboating’. Many of the all-mode QRP rigs on the market run down to at least 10v, with the 703 pictured above bottoming out at 9v. So not only can you run more efficiently, you can run longer off the same batteries, which equates less weight, which means more room for other important stuff if planning on long term field operating.

But what’s the REAL difference where it matters- getting through?

Decibel (dB) levels are the measurement of received signal volume and an indication of signal strength. All things being equal, meaning the same antenna, same transmission line, same ground, same atmosphere conditions, etc, 100w will have 13dB gain in strength over a 5w signal. The general rule of thumb is that 3dB difference is twice the power output and 10dB being ten times the output. Since 6dB is roughly 1 S-Unit, we’d get a little more than twice the signal gain over our 5w QRP signal. Looking at our current consumption figures, it’s starting to look more logical to have that QRP rig over lugging twice the battery capacity to the field, especially if part of our job as RTOs is monitoring.

Conversely we know that not all things are equal. The current solar conditions are pretty rough on average, with occasional great openings on 20 down through 160, and having that extra signal strength could come in handy. Since most of the newer QRP rigs can run up to 10w, giving us 3dB extra with the same superior efficiency, some of the potential problems are overcome. But this leaves other issues to address, such as the transmitting mode itself, the feedline, and the antenna.

Single Side Band (SSB) or more commonly known as “phone” operating is simply talking into the mic while transmitting. While it’s the easiest to copy for beginners, it’s also the most susceptible to interference and signal loss. Continuous Wave (CW), the propagation mode for Morse Code, holds a 13dB gain in strength at the same power level as SSB, meaning that 5w CW signal will be equivalent to a 100w SSB transmission. So while the digital modes also possess quite a bit of signal superiority over SSB, CW only requires a key and your time and patience to learn. Due to its simplicity, its a worthwhile skill to learn as an RTO.

The last piece of the efficiency puzzle is the antenna system itself, with the feedline and radiating elements being of equal importance. On HF, loss figures are not that big of an issue, so you can get away with running cheaper coax such as RG-58 or RG-8X and have little issues. But keeping as short a transmission line as possible IS important, for efficiency’s sake. The radiating element itself should be cut to as close a resonant length as possible providing as close to a 1:1 Standing Wave Ratio (SWR) as you can get. SWR is the measurement of your antenna’s efficiency given in as a ratio between power reflected back and power sent forward, with 1:1 being a perfect 100% efficient and 2:1 being 50% efficient, and so on and so forth. For a basic dipole, where each leg is quarter wavelength long on HF, we can calculate our necessary antenna length for each of the two dipole legs by using the formula:

234 / Frequency= Length in Feet

So since we planned out our transmission schedule and frequencies using our Signals Operating Index (you planned that, right?) we can create the antennas we need as close to resonance as possible and making us that much more efficient, meaning a much higher probability of success.

So where does this leave us? For those new of upgrading their capabilities, 100w is the way to go. It has the least learning curve getting you on the air and overcoming many of the more technical factors that inhibit efficient communications. But if you’re planning on working in the field in any capacity, be it recreational or more of a preparedness stance, a QRP rig provides a level of efficiency that the higher-wattage rigs cannot match. Both are very important, offering regional capability networking other operators in a way no other conventional means can match. While success includes learning quite a bit about the art of communications, its a worthwhile goal going far beyond simply having stuff. Further, simply having the radio or the license is not enough- get the training and get on the air. It’s the only way.