It is possible to use many forms of equipment for QRP operation. It is often possible to use the main station rig in a QRP mode, but for many people QRP operation means a little more - operating with equipment they have built themselves.
As a large number of people enjoy QRP amateur radio, there is a large variety of equipment, ready built, in kit form or circuits that can be built relatively easily.
Transmitters, receivers, antennas and also ancillary equipment like antenna tuners, SWR metes and the like are often simpler, lower cost and easier to use than some of the top end high power equipment.
QRP transmitters & transceivers
There are several options for people wanting to use QRP equipment, each has its own characteristics and will be right for some people rather than others.
- Use existing transceiver: It is possible on many HF transceivers to turn the output power level right down. Some give a reading of the output power, but if not, then many SWR meters also have a power measurement capability, so it is possible to check that the output power is limited to the QRP maximum, or possibly lower if that is needed.
The advantage of taking this approach is that if an HF transceiver is already available, then no further equipment is needed and no changes need to be made within the shack.
- Buy a purpose built QRP transceiver: There are a number of purpose built transceivers that are available and thee can be bought and put to good use. Ten Tec make a number of QRP HF transceivers for which at least some offer excellent performance and some have possibly the best CW break-in or QSK capability - you can hear between the dots at 25 words a minute and more.Tec Tec is not the only manufacturer of QRP equipment by a long way. Other famous names like MFJ and many others offer ready built equipment that performs well. However like any purchase, it is necessary to check out the data sheets and reviews
- Build a kit: One of the joys of QRP is that equipment can be very simple and this makes it ideal for home constructing. There are many kits available from a variety of sources for transmitter and transceiver kits.
These kits can reduce the costs and also give a real sense of achievement when they are built and working. It is for this reason that amateur radio QRP operation is very popular. A variety of kits are even available via Amazon.
However beware, some of these kits do not come with instructions, so it is necessary to do some research on the Internet to find out even the basics like the component numbering and placement on the board. Fortunately these kits are so cheap, and the instructions are normally available elsewhere so it is not an insurmountable problem, but it is necessary to be aware of this issue.
- Build from scratch: There are also many circuits available for which he components can be bought separately and then the circuit can be built. There are circuits for both QRP transmitters and transceivers. With the focus generally being on Morse or CW operation, this means circuits can be very much simpler than would otherwise be the case.
The fact that the focus is generally on CW / Morse operation means that circuits and equipment are very much simpler than would be the case if SSB was used for example. This reduces both the cost and complexity, bring amateur radio into he reach of many more people.
Receivers for QRP
Although QRP transmitters are also transceivers, this is not always the case by a long way. Some simple QRP transmitters may only act as transmitters and in this case a station receiver will also be needed as part of the QRP equipment line-up.
Again there are several options:
- Use receiver from existing station transceiver: One of the options open to many people will be the use of an existing station receiver included within the main station transceiver. If this is done, then the antenna switching will need to be accommodated in the transmitter, although this is normally the case. Using equipment that is already available, not only reduces the cost, but also means that it is faster to get up and running.
- Use a separate receiver: Some QRP stations may use a separate receiver. It may be an older receiver sued as a second receiver for the station, or possibly bought for the purpose. There are several options open:
- Modern receiver / scanner: There are several HF receivers that are available on the market that are available to buy new or second hand. Some scanners also cover the HF bands and can be used, but check they can operate satisfactorily for this purpose.
- Old war surplus receivers: Some QRP stations like to use old vintage valve communications receivers. Although less widely seen these days, they can still provide good service.
- Build a kit receiver: There are some receiver kits tat are available - often from the same companies that manufacture QRP transmitter kits. There are two main types of receiver that are used:
- Superheterodyne receiver: The superhet radio is the form of radio receiver that is most widely used for communications applications. It requires the incoming signal is converted down to a fixed frequency intermediate stage where the majority of gain and filtering is provided. To achieve the frequency conversion a mixer and variable frequency oscillator are used. To prove the adjacent channel selectivity, sharp filters are required. IN top performance receivers high performance crystal filters are used, or alternatively digital signal processing techniques are employed. These are costly and therefore the performance of any entry level kit receiver will not meet that of more costly sets. That said adequate performance is often achievable.
- Direct conversion receiver: A direct conversion or DC receiver adopts the approach of converting the signal down to audio without the need for an intermediate frequency stage. This type of receiver is ideal for CW (Morse) reception and single sideband, but it is not normally used for AM or FM, etc.
Audio filtering usia simple op-amp audio filters can be incorporated, but even without a specific audio filter, signals are not heard outside the audio bandwidth
The direct conversion receiver does have some drawbacks - one being the image response. As a signal is tuned in the beat note is heard between the signal and the receiver local oscillator - as the receiver is tuned further into e same direction, the beat note goes to zero and then starts to rise up again. In this way there are two positions where the signal is heard. In many instances this is not an issue, but if interference levels are high then it can make copy more difficult. Another issue is that strong off-channel signals can overload the mixer and early audio stages.Otherwise this form of receiver offers a very simple and effective approach for home construction.
- Build from scratch: This option tends to be used less these days. Although there are some good designs available, any advanced designs require a large investment in time and effort. The more basic designs can still be covered relatively easily, but may good kits are available.
Antennas for QRP
The antenna is an important part of any station. Using low power it is essential that an efficient antenna system is used, if lower power levels are being used, then it means that the performance oft he antenna is even more important. Loss in signal strength from the lower power being used can be compensated by the use of a highly efficient antenna. Accordingly beams on high towers are the ideal solution for QRP stations.
However, iIn keeping with the spirit of QRP many people like to make and erect their own wire antennas. Dipoles and end fed wires are very popular, and there is a great amount of scope for experimentation and improvement of the performance of these antennas.
To obtain the optimum performance, these wire antennas should be as high as reasonably possible, in the clear, i.e. not close to obstacles that might detune them or absorb the signal, and if possible in a good high location.
A typical dipole antenna might be a dipole like the one below:
As height is a key issue, the centre section of the dipole, that normally has the highest current and hence radiates most can be raised and the ends sloped away. This form of antenna known as an inverted V has many advantages for the typical QRP station.
There are many antenna options that can be considered. Horizontal antennas tend to work the best. Verticals have a much lower angle of radiation and are used for much longer distance contacts. For QRP operation the path loss incurred for long distances may be too high for the power levels used and therefore they may not be as good.