QRP Australia
QRP Australia
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Suggested QRP Projects
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So you want to build a QRP rig? It doesn't matter what band it operates on, but you want it to provide the most fun for the least outlay (and fruitless CQ calls). You are not worried whether you work DX or local stations, but your signal should be strong enough at the other end to have a ragchew should this be desired. It needs to be stable yet frequency-agile, fairly simple and have a reasonable receiver. The parts to build it must be readily available and not cost a bundle.
If the foregoing is your idea of the ideal first QRP rig, the following "best projects" will be of interest. The first two are single band CW rigs suitable for the beginner, while the last two operate on several bands or have voice capabilities. Construction costs range from about $30 (for an 80m QRP CW transmitter) to $100 or more for a multiband and/or multimode transceiver. However, these costs can be reduced if you use salvaged components and home made enclosures. Best Project #1 If you live in SE Australia, and can operate during daylight hours, 40 metres is probably the best band for QRP, particularly if you do not have room for an efficient 80 metre antenna. A VXO CW rig for this band is all that is required for good results.
Choose your crystal frequency carefully - 7.030 MHz (though the international QRP frequency) is too high for Australian conditions. Order your crystal in an HC6/U holder for maximum frequency shift. A 7.026 MHz HC6/U crystal ($19 from J&A Crystals, 20 Delville Ave Mentone, Vic, 3194) allows coverage of the 7.025 MHz CW Net and is a good choice.
The transmitter section could use a simple transistor VXO circuit (capable of up to 15 kHz coverage) followed by a buffer, then a driver and finally a power amplifier. A 2N3053 or BFY51 would give close to 1 watt output. However, 2-4 watts may be available if a BD139, IRF510 or 2N3553 PA is used instead. A medium sized PNP transistor can be used to key the rig by switching the PA transistor's collector or drain supply.
This simple transmitter could be used alongside a "black box" receiver or transceiver to get on air quickly. A direct conversion receiver section could be added later. You can't go past the NE602 for simplicity and ease of use, so use this as the product detector. A 741 audio preamp and a NPN transistor audio amplifier to drive a pair of high impedance phones complete the project. However, an LM386 or HEF4007 (biased to linear operation) may be a better proposition if you need to drive either a speaker or low impedance phones. One stage of op- amp audio filtering (700-800Hz) will suffice for local operating during the day, while a second stage is essential for night time operating and DXing.
Regular daytime contacts between 300 and 800 km are common, with the occasional 3000 km contact possible at dusk or during the evening. A transmitter very similar to the one described was featured in the WIA's Amateur Radio magazine (January 1996 issue). Best Project #2 Those unable to operate during the day would be better off constructing equipment for 80 rather than 40 metres. While night time QRP contacts are possible on 40m, they are often difficult to make.
Though designs abound for crystal-controlled equipment, and a two or three transistor crystal controlled transmitter on 3.530 MHz can be fun to use, the availability of 3.58 MHz ceramic resonators puts frequency agility within everyone's reach. A pulling range of approximately 100 KHz, neatly covering the VK Novice portion of 80 metres is possible with a ceramic resonator. However, for ease of tuning (especially without a vernier reduction drive) it is best to restrict the coverage to the CW portion of the band only.
A CMOS IC, a VMOS FET (eg VN10KM) and a PNP keying transistor can form a practical 1-2 watt 80m CW QRP transmitter. For full details, see Amateur Radio magazine for July 1995, page 4 (note the polarity of the zener diode is incorrect on the schematic). A suitable receiver could be along the lines of that described earlier for the 40m transceiver. Best Project #3 Maybe you already have a QRP rig for 80 metres, but want QRP capabilities on the higher bands. If so, a two or three band QRP transmitter or transceiver is a good project, particularly if QRP DXing is your aim. I'd suggest you start with a stable VXO on 7 MHz. Use a 7.020 MHz HC6/U crystal and experiment with various VXO circuits until you get one that gives you at least 10 kHz frequency shift. Then build a buffer stage for the VXO. Experiment with various multiplier circuits to get output on 14 and 21 MHz (in addition to 7 MHz). Band switching is the hardest thing to arrange here, and three or four bands is appreciably harder than two band coverage. A keying circuit, a power amplifier (possibly preceded by a driver stage) and a set of pi networks for the appropriate bands complete the project. Refer to the G-QRP Club Circuit Handbook or Solid State Design for the Radio Amateur for examples of designs that you could use. Best Project #4 Those wanting something for voice operation could try a simple ceramic resonator-controlled DSB direct conversion transceiver for 80 metres. Such a rig could include a bipolar transistor Pierce variable ceramic resonator oscillator, a NE602 balanced modulator and a 741 speech amplifier. The receiver could use similar components. The design would look a lot like some of Drew Diamond's recent designs ("TCF80", "Simplex", etc), but would be DSB and not SSB. The 40 metre version could be crystal-controlled, but its best to use some sort of circuit for frequency agility - ie a VXO, a ceramic resonator oscillator doubled from 3.5 MHz or a a free-running VFO. DSB rigs are exceptionally rewarding projects, but require a little more constructional experience than the aforementioned CW rigs. It is suggested that you build a CW rig before tackling a voice transmitter. Best Project #5 If you're in Melbourne or anywhere where there's regular 160m AM activity, a small AM rig for 160 metres can be a lot of fun. You could modify an ex-marine 2 MHz transceiver or build a transmitter yourself. Such a rig may use a commonly-available (and cheap!) 1843 kHz crystal, have two or three RF stages in the transmitter and use a modulator such as an LM386. For a receiver, a modified pocket transistor radio could be put into the same case as the tranmitter, making a nice compact transceiver.
Any of the above projects form the basis of a practical QRP installation, ideal for home or portable use. More information on what to look for when building or buying QRP equipment can be found by clicking here. If you want to know more about home construction, click here. For examples of projects you can build, click here.
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