Technical Articles

The Pros and Cons of Using an Amp with QRP Radios

Less is more. QRP (low power operation) is becoming quite popular among hams who take a minimalist approach to amateur radio communications. Some radio amateurs who are licensed to use full legal power often prefer QRP operation. Why? It gives them a sense of satisfaction and provides a whole new set of challenges in terms of radio operating skills. 

So how low is low power operation? QRP means ham radio operation with 5 watts or less output for digital and CW, and 10 watts PEP output or less for SSB. Some hams are known to use even less than 5 watts, sometimes operating with as little as 100 milliwatts. Extremely low power—1 watt and below—is often referred to by hams as QRPp.

But why would anyone except a masochist want to operate with 5 watts output or less? As the ham curmudgeons say, life is too short for QRP, especially at the low end of the solar cycle. These members of the amateur radio community believe it’s more productive to just crank it up to 100 watts (or more) and quickly establish a solid contact. To them, higher power is the way to go.

Fixed vs. Portable Operation

Your choice of operating from a permanent location, such as your house or a temporary/portable site such as a park or campground, will have a huge influence on your QRP vs. QRO (high power) decision. To further complicate things, portable means different things to different people. The amateur who wants to operate from an RV or radio club communications trailer faces a different set of issues than one who wants a radio setup that will fit in a backpack.

SOTA (Summits on the Air) and POTA (Parks on the Air) operations are examples that call for lightweight portable gear that can fit in a backpack. There are portable HF amplifiers available in the 45-100 watt range that are small enough to fit and weigh around 5 pounds.

During Ohio State Parks on the Air several years ago, we used a QRP SDR transceiver running 5 watts on SSB, attached to a half wave end-fed antenna, for an hour. The next hour, we added a 50 watt amplifier to the mix. In our unscientific test, we more than doubled the number of contacts in the log using an amplifier.

However, don’t forget that the amplifier also requires a power supply. The battery you use for your QRP radio won’t power both adequately, meaning you’ll need to bring additional batteries to keep you on the air for several hours. They will take up space and add weight to your backpack. Fortunately, currently available lithium iron phosphate (LiFePO4) batteries are fairly compact and only weigh a few pounds.

For operation from a car, RV or AC power, batteries aren’t an issue. You simply use a 13.7 volt supply or a car battery to operate the complete station.

What Do You Gain?

Common sense tells us that QRP signals can get lost among those from more powerful stations. But they’re not as lost as you might think. The difference between 5 watts and 100 watts is approximately 13 dB. So a signal that is S-9 at 100 watts is S-7 at 5 watts—a difference of slightly more than two S-units. An amplifier can make a difference between being heard or not under marginal conditions.

To summarize:

Amplifier Pros

  • Increase in signal strength, especially helpful on 160/80/40M
  • Better results for contesters
  • Usable base or portable

Amplifier Cons

  • Defeats the purpose of having a QRP rig
  • Additional/larger capacity batteries required for portable use
  • Additional weight/station components for portable use
  • Extra expense

Another consideration we haven’t discussed is the importance of the antenna. For best results you need the best antenna you can put up—it’s as simple as that. A good antenna can make up for the limitations of QRP power levels or enhance the performance of your 100 watts, however you choose to get there.

Also, if your radio has an audio compression control, you can gain up to 3 dB if it is adjusted properly.

An Alternate Approach

By the time you figure out the cost of a decent amplifier and QRP radio, you could end up spending more than you would for a moderately priced 100 watt transceiver. You could actually spend more for the amplifier alone.

There are several mobile transceivers that could be considered for portable use that are relatively lightweight and don’t take up a lot of space. The Yaesu FT-891 is capable of 100 watts of output. If you don’t mind having a separate control head, the ICOM IC-7100 will also give you 100 watts (be sure to check for current pricing and available manufacturer rebates). Of course, you can set the RF output to 5 or 10 watts for QRP operation if you’re up for the challenge–that also goes for most other 100 watt transceivers. Just be sure to measure output with a wattmeter of known accuracy.

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