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QRP Equipment

FT817 R4020 QRP rig

There is a wide range of equipment available for the QRPer. This includes 100 watt transceivers than can be wound down to QRP, purpose built QRP and portable radios, build-it-yourself kits and building gear from scratch. Keep reading if you want to know what to buy or build and get results with QRP.

QRO equipment wound back to QRP

Today's 100-watt transceivers can often be wound back to deliver QRP power levels. Their multimode multiband coverage and other features make them attractive to the operator who wishes to try QRP but also retain QRO capabilities.

A particular benefit is their impressive array of interference-beating features, such as noise blankers, notch filters, variable tuning rates, IF shift and digital signal processing. For this reason, this gear provides excellent results when trying to receive marginal signals from distant QRP stations. If you are only going to have one HF transceiver there's a strong case to make it a 100 watt unit as these deliver superior value on a watts per dollar basis.

What are the disadvantages of using 100 watt transceivers? Compared to dedicated QRP radios they are bulky, heavy and draw high currents on receive. It is not uncommon for a modern HF rig to draw 1 to 2 amps just on receive, ie more than what most QRP radios use on transmit. While not a problem for home use, this last factor alone makes large transceivers a poor choice for portable work due to the weight of batteries required.

I briefly compare the features of current model 100 watt transceivers here.

R4020

Commercially-available QRP equipment

Today's main choices include the Yaesu FT-818ND, the Icom IC-705 and the Elecraft KX3. All three are multiband and all mode. But transistorised QRP gear started in a more modest way. I'll fill you in on some history before discussing the latest stuff.

When QRP first took off in the late 1960s, spurred by the increasing availability of solid state RF devices and the rediscovery of direct conversion receivers, a number of American manufacturers produced equipment specifically for QRPers.

Heathkit produced the HW7/8/9 series of CW only transceiver kits during the 1970s and 1980s. Of these the HW7 drifted and had a poor receiver, the HW8 was a much improved design and is still usable while the HW9 had more bands and mixed reviews.

SSB QRPers of that era could buy Ten Tec's Argonaut 505, 509 and 515 models. Though lacking today's refinements, they performed well and are still sought after despite their large (and not particularly rugged) enclosure, crude tuning dial and odd choice of power and antenna connectors. $200 to $250 is a fair price on the used market for a working Argonaut 509.

Japanese QRP rigs, designed for their 10 watt novice licence, were imported into Australia in big numbers and frequently appear secondhand. Examples included the Yaesu FT-7, Yaesu FT-77S and Kenwood TS-120V. These rigs are still good performers, but lack 160 metres, some HF bands, and digital signal processing found on newer transceivers. By today's standards they are bulky and are best suited for home or car use.

Less well known QRP rigs of the 1980s include models by Shimizu Denshi, MFJ, Mizuho and the ironically-named Tokyo Hy-Power. These may only cover a single band and be CW or SSB only. They also had analogue VFOs and dials. They were available for only a short time and/or were rarely available outside Japan.

The first 'modern' QRP radios, with all-HF coverage, digital dials and CW/SSB modes were the 'cube' Index Labs QRP Plus and the rugged SGC-2020 transceivers. These came out in the 1990s. There was also a blossoming of QRP kits from various US QRP clubs, including from designers who would later form Elecraft (discussed later).

Mainstream ham manufacturers reentered the QRP field from the early 2000s. Possibly the longest running and most successful QRP transceiver ever is the Yaesu FT-817 (pictured above). Unlike previous QRP rigs, the '817 operates on all bands between 1.8 and 450 MHz and has a compartment for optional internal batteries. It provides 'big rig' performance in a tiny package and has provoked renewed interest in back-pack and pedestrian mobile operation. The FT-817 came out in 2001. The FT-817ND was a minor update a few years later with more robust final amplifier stage. That was in production for the better part of 15 years. It was only stopped when the FT-818ND came out in 2018. The difference between that and the FT-817ND are not worth mentioning; if you have an FT-817ND you wouldn't bother updating to the '818. "If you're on a good thing stick to it" seems Yaesu's motto and they've certainly earned it with the 817ND/818ND series as you've seen in many of my videos.

Icom took a different tack. They came along with the IC-703 in 2003. Maybe they saw the success that Yaesu was having with the '817 and wanted to join the party. It's HF-50 MHz only and cosmetically looks like the hugely successful '90s era IC-706 mobile rig. The IC-703 served a slightly different market to the Yaesu. It was chunkier but ran 10 watts with what some considered a better receiver. And its display wasn't so tiny. A SOTA operator or VHF freak would pick the smaller Yaesu while a drive-in portable operator, or someone who wanted a low power HF rig for home, might opt for the less fiddly Icom.

The FT-817 became the 817ND and continued to sell. Even though it was by now a 15-year old design there was nothing comparable, especially on a bands per dollar ratio. Kenwood's best years were behind it, with it being a very distant third of the 'big 3'. Ten Tec in the States was like a classic hits radio station, with its big numbers from the '70s, '80s and '90s. It did however offer economical rebadged Chinese gear like the nice little R4020 40 & 20m CW transceiver for a while. Icom stood by, concentrating on its DSTAR offerings on VHF and UHF. However, as you'll see later, it would return to the portable QRP market after attending to some unfinished business with SDRs in the lower to middle price point.

The favourite choice, amongst those with the money, was something from Elecraft. Elecraft replaced Ten Tec as the main US-based maker of HF ham gear. Elecraft started before the turn of (this) century with the K2 kit radio. Inititially low power CW only you could get upgrades for SSB and 100 watts. It was highly regarded for its performance particularly on receive. Two years later came the K1, a smaller CW-only rig for 2 to 4 bands. From there Elecraft branched in two directions with the KX series. The KX1 was low drain CW-only for the backpacker/summits crowd while the KX3 was getting more modes, more bands with a better receiver and higher output power than the FT-817ND. Shaped more like a brick, it had a bigger display than the Yaesu but wasn't cheap, and in my view was less robust. Elecraft later released a cheaper KX3 lookalike called the KX2 with a smaller case and fewer bands. That did everything most portable operators needed. Especially when imported into Australia its price was high so many either stuck with the long-in-the-tooth but versatile FT-817ND or tried some of the cheaper Chinese QRP rigs coming out (eg the Xiegu series). If small size and low drain are top considerations the LNR CW-only MTR series is something else to consider.

What was Icom doing? They were developing what was to become the IC-7300 SDR-based home station transceiver. Situated at the lower-middle price range, this proved a sales sensation from its release in 2016. With that sorted they returned to the QRP market with the new IC-705. That's an HF/50/144/432 MHz portable SDR QRP rig with the same touch-screen as the '7300. Its main competitor is the Elecraft KX3, with a similar 'house brick' shape and battery arrangement. The '705 runs 10 watts output and has a lot of features the Yaesu lacks. On the other hand it's much more expensive and lacks the dual antenna sockets. And I like the Yaesu's robustness and shape for pedestrian mobile use. Early indications are that the IC-705 is popular but it doesn't replace the FT-818ND as the smallest QRP rig with the most bands with the least money. More about the FT817/818 here.

Quality, reliability, finish and customer service varies, especially from the newer manufacturers. Then there's overall value for money. It's always a good idea to to read reviews on sites such as eHam.net before purchasing.

 

 

Disclosure: I receive a small commission from items purchased through links on this site.
Items were chosen for likely usefulness and a satisfaction rating of 4/5 or better.

 

qrp kit

QRP kits

QRP constructors have a variety of kits from which to choose. These range from no-frills crystal-controlled transmitters to multiband CW/SSB transceivers. QRP kits can be club projects for members or be available on the commercial market. Some are even designed and produced here in Australia. The results obtained from a good kit on the right band make this choice worthwhile, especially if less experienced or time-poor.

Things to think about when choosing a kit include:

* Modes and bands provided
* Whether the output power and receiver performance are sufficient for routine communications
* Whether it is fixed frequency or frequency agile
* Whether it is complete or short-form (ie board and parts only)
* Whether it is transmitter only, receiver only or transceiver
* Complexity of construction and experience required, including use of surface-mount parts
* Whether you think you can build it (see supplier websites for instructions)
* Reputation of manufacturer and reviews by others who have built the kit

Avoid both extremely simple and extremely complex kits unless you're experienced and know what to expect. Most people find there is a 'sweet spot' where kits are neither too expensive nor complex yet achieve many contacts.

Bare bones 'minimalist' kits (such as the well-known Pixie series) have rudimentary receivers, weak transmitters and a fixed operating frequency. Getting contacts is frustrating because other stations must find you rather than you find them. They may use only three or four transistors and only put out a few hundred milliwatts. Transmit output filtering, keying quality and receiver selectivity may also be compromised.

Only attempt this type of kit if you are looking for a novelty project or are willing to call for long periods between contacts. Alternatively build the circuit from scratch, not using a printed circuit board. That gives flexibilty to add improvements. If your heart is still set on buying a kit, pay that little bit extra and get one that will be a pleasure to operate for years to come.

Good candidates for a first-up QRP kit

Single band is preferred as more bands means more complexity. Select a popular band that will be open throughout the solar cycle and produce contacts at the times you plan operating. VKs shouldn't rely on reports from overseas - activity locally is less, and a minimalist rig that will get contacts in more populated countries may not as much here.

40 metres is my recommendation, providing easy and regular communication up to approximately 1000 kilometres. 20 metres has the added excitement of working DX but contacts are much harder to get and there are fewer conversations between VK stations. 80 metres is good if most of your operating is at night, though voice is preferred over CW due to higher activity.

Higher HF bands like 17 to 10 metres offer great DX opportunities but do not open frequently enough for them to be your only band. Even 20 metres can be a struggle. It can get busy during good conditions (and contests!) but there is less chat and less local working than 80 and 40 metres. Its DX culture can make 20m contacts harder than on the lower HF bands.

Transmitter output power should exceed 1 or 2 watts. Anything less is frustrating. A kit with a BD139 or IRF510 final transistor should put out enough power whereas one with a 2N2222 will be too weak.

A degree of frequency agility is essential. The better kits will have a DDS VFO will cover all the band. If a kit has a digital frequency display the chance is it also has a DDS.

A second and simpler choice is a well built ceramic resonator or wide swing VXO with two crystals and a good variable capacitor. This can cover a worthwhile section of band. A ceramic resonator can span 100 to 200 kHz while a wide swing VXO should cover 15 - 50 kHz. Kits that use varactor diodes and potentiometers for VXO tuning may cover a lesser range than those with air spaced variable capacitors.

Check that supplied crystals or resonators suit local activity before buying kits that only cover a band segment. For instance US CW QRPers generally use higher frequencies than those in most of the rest of the world on 80 and 40 metres. A 7040 kHz crystal, for example is fine for various digital modes but not necessarily for CW. CW transceiver kits are available from some of the suppliers listed below. Any of these would be an ideal for trips and draw less current than prebuilt commercial rigs.

DSB kits are simple and and fun. An SSB kit is a step up and more advanced. That is unless the board is pre-assembled like with the Bitx and uBitx. There you just need to find a case and connect the off-boards parts. You get much of the kit building experience without putting as many hours into construction. More on the uBitx here.

Multiband QRP transceiver kits represent another advance. Unless largely pre-assembled (like the uBitx) they are recommended for more advanced constructors only. They have become more prevalent thanks to wide-range DDS VFOs and put the assembly of multiband gear within reach of more.

If a kit radio appeals but you don't want to build it check to see if the manufacturer offers a pre-built version. This option would also suit Australian Foundation Licence amateurs who cannot legally make their own transmitter.

Another option is to scour the hamfests and second hand ads. Brands to look out for include Heathkit, Small Wonder Labs, Hendricks, Oak Hills Research, Elecraft and OzQRP. Information on these is widely available on the web.

You'll also find reviews of prebuilt and kit QRP rigs on eHam, while some have their own email list that discuss their features, quirks and modifications in detail.

Current QRP kit suppliers

The following are known suppliers of QRP kits a step or more up from the cheap Pixies and their variants. Listing here does not imply endorsement.

Bliss Radio (SSB/CW transceiver)

Breadboard Radio

CR Kits

Four State QRP Group

HF Signals (Bitx/uBitx)

Kanga Products

Kits and Parts (VXO kits)

LZ2JR (RGO One)

mcHF QRP transceiver

Minikits (mainly VHF & up)

OzQRP (MDT/MST series)

QHR kits by EA3GCY (Iler and others)

QRP Guys

QRP Kits

QRP Labs (QCX and WSPR kits)

QRPver

QRVTronics

Walfords (Variety available)

WA3RNC (40m QRP CW)


beach 40 dsb txcvr

Homebrew QRP equipment

QRPers also have the option of building their own rigs. And a surprising number do. Homebrewing is the way to go if you want a rig that is personalised to your interests and preferences. For example, you may require a particular band combination and an unusual ability to switch audio bandpass and notch filters for best reception. A homebrew rig may also be a platform for development of a high performance receiver, or novel transmitter arrangement, for example.

Some general components for homebrew transmitters and transceivers can be obtained from the usual parts suppliers, while the more specialised parts (toroids, variable capacitors, NE602s, etc) can be found at amateur hamfests, junk sales, eBay or purchased by mail from QRP clubs or specialist online suppliers.

Transmitter or Transceiver?

A key decision for the constructor is whether to construct a transmitter or transceiver. A transceiver is easier to operate and less bulky - major advantages for portable operating. However a transceiver is more complex, especially where many stages are common to both the transmitter and the receiver.

A transmitter is recommended over a transceiver for the beginner as it uses fewer parts and is easier to troubleshoot. In many QRP transceivers, the receiver may account for two-thirds of all components used. Leaving out the receiver makes for a simpler and quicker project that is more likely to work first time. Also, the use of an outboard receiver means that the transmitter/receive frequency offset circuit can be dispensed with, further simplifying circuitry. Another point in favour of the separate transmitter/receiver approach is that most QRPers will already have a suitable communications receiver available. The performance and ease of use obtained will typically be better than that from a simple homebrew receiver.

A good plan is to build the transmitter in an oversize box. Once the transmitter has been got working, it can be expanded. For instance, a direct conversion receiver can be added. Or an extra band. Or, maybe even the parts required to generate a DSB or SSB signal.

Choosing a design

What type of transmitter circuit should you start with? Sure, it's very easy to build a simple 80 metre QRP Morse Code rig. Just one or two transistors and a 3.58 MHz TV colourburst crystal, and you're on the air. But will the rig sound OK? Will you get contacts? Or will the rig cause you to give up QRP because no one is responding to your CQs?

This website is devoted to practical QRP. QRP that works. QRP that's fun. And to get the most enjoyment from QRP, you need to know something about the capability of your equipment so that you don't expect too much and become disappointed when your hopes do not materialise.

Be selective about the type of QRP rigs you build. It must be fairly simple and not require too many hard to get parts. Secondly, it must be put out enough power to be heard on the air. Thirdly, it should be frequency agile over at least a segment of the band. The following sections explore these points in depth. The author's minimum standards for homebrew rigs should also assist the builder to cull the good from the useless in the hundreds of circuits available.

Power

What is sufficient power? Though this depends on the distances you wish to work, I would say that an inexperienced amateur aiming to make regular contacts with powers of less than one or two watts on any HF band is going to be disappointed. Sure those milliwatt rigs you see described in foreign magazines and on the web do work, but remember that Europe and the USA have far more amateurs per square kilometre than we have in Australia. As it's so easy to build one or two watt transmitters that there is little sense in settling for less unless you specifically want to do experiments in milliwatt communications.

I would recommend powers of 1-2 watts as a practical minimum assuming you are using a reasonably efficient antenna (eg a full-sized dipole). Though there will be times when more power than this will be required (eg when static is bad), you should be rewarded by reasonably frequent contacts up to several hundred kilometres, and the occasional two or three thousand kilometre contact with 1-2 watts. On 40 metres 1 - 2 watts is again sufficient for distances of up to about 1000km, and the proportion of Q5 signal reports tends to be higher than on 80.

On 20m and up, Europeans and Americans can be worked from Australia at the 5-watt power level, especially if portable overlooking water. Don't expect reliable DX contacts from home with this level with low dipole or vertical antennas, however.

FT8 is a highly effective mode, and contact up to about 3000 km are possible almost every day with QRP power levels. JS8 is less active but is recommended as a more personalised alternative. WSPR isn't a contact mode as such but is highly efficient. If you get a buzz from a 20 milliwatt signal being detected on the other side of the world then it could be the QRP mode for you.

SSB requires more power for comparable results, but even so 5 or 10 watts can be rewarding, even in the middle of the 20 metre 'kilowatt alley' when conditions are favourable. Otherwise you might only be able to work as far as 2000 - 3000km. Very low output powers can be very successful on the higher bands, but you need to be there at the right time - the kilowatters may enjoy DX for hours, but the QRPer must be there when the band is optimum.

Frequency agility

Then there's frequency agility - being able to move around the band, rather than being stuck on a single frequency. Many home brew QRP transmitters are crystal-controlled. Most of them also sit on the shelf gathering dust and are seldom used. Why? Being locked on one frequency severely hampers your operating success. You could be calling CQ, but not be getting any replies. Then 5 kHz up the band, you hear another station also calling CQ. If you were frequency agile, you could move to the other station's frequency and most likely obtain a contact. Instead, you remain on your frequency, hoping that the other station will not get a reply, stop calling, tune around and eventually find you. A lot of people build simple rigs, have one or two contacts, and not use them again because getting contacts is sheer hard work.

The disadvantages of crystal control are greatest with QRP. Unless someone happens to start calling on 'your' frequency, the only way to get contacts is to call CQ yourself. As many people tend to reply to CQs from stronger stations only, your chances of getting a reply are reduced if your signal is weaker. The successful way to get contacts with QRP is to 'search and pounce'. Either reply to CQ calls from other stations (you know at least someone is listening for your call), or 'tail-end' contacts that are concluding. Both of these techniques are only really possible if you can move frequency. And, if there is not much activity around, and you do wish to call CQ, chances are better if the call can be made on a perfectly clear frequency. The probability of finding such a frequency is of course much greater if you can operate everywhere in the band.

Another limitation of crystal control is that your crystal may not be in the most active part of the band. For example, 3.58 MHz TV colourburst crystals are conveniently in the middle of the 80 metre Novice allocation. However, most CW activity is below 3.550 MHz. Operators seeking CW contacts will not often be tuning across 3.58 MHz. So, the chances of getting a response are reduced as you are not where most potential contacts will be listening.

Even crystal-control on the so-called International QRP Frequencies (eg 7.030 & 14.060 MHz) can be very limiting, at least in VK/ZL. These frequencies are sometimes clogged by strong digital mode QRM, and are made useless as a result. This disadvantages the constructor who has built a rockbound 'OXO' or 'Cubic Incher' rig that is stuck on the single frequency. Though authors describing such projects invariably report great success with their one or two transistor creation, bear in mind that they in Europe or North America, where the amateur population is at least 20 times Australia's. Attempts by Australian amateurs to operate such transmitters often lead to fruitless CQs, followed by grave disappointment with the lack of contacts achieved.

To summarise, because 'search and pounce' (answering calls and tail-ending) is the best way to get contacts, frequency agility is essential for the QRPer. Use nothing less than a VFO, good VXO, or stable variable frequency ceramic resonator oscillator to succeed with QRP.

Mode

Morse transmitters are the simplest to build. A simple VXO CW transmitter can be built in an afternoon and work stations near and far. Watt for watt they are more efficient for longer distance communication, especially on crowded HF bands like 20 metres.

If you are building a voice rig, should you choose AM, double sideband suppressed carrier (DSB) or SSB? An SSB rig is a challenging project, and is not recommended unless you've already built CW and DSB transmitters. So, for the newcomer (and even for many experienced amateurs), the choice is between AM and DSB.

AM was used prior to the advent of SSB, and still has a following on some bands (especially 160 metres, to a lesser extent on 80 and 40). However, many SSB rigs do not have AM and it may not always be easy to resolve a weak AM signal on an SSB transceiver. Because AM signals include a carrier that does not contribute to the intelligibility of the signal, AM is less efficient than SSB, and more transmitting power is required to make oneself heard. However, AM still has its uses. The speech quality of AM is generally better than DSB or SSB. Where you have a small group interested in local contacts only (such as within a country town or small city), a homebrew AM rig would be a fun project, particularly on 160 or 10 metres where there is plenty of band space. Ranges of up to about 5km can be achieved with powers of under a watt.

DSB has an equivalent bandwidth to AM, but has no carrier. Thus it is a more efficient mode. As well, DSB is fully compatible with modern SSB equipment, and unless you tell them, many SSB stations will not know that you are using DSB. The combination of a direct conversion receiver and DSB transmitter is highly recommended for the Novice wanting to build an HF voice station, and because of the similarity of DSB and SSB. Also, DSB transmitters can later be upgraded to SSB by adding extra circuitry. DSB is particularly recommended for bands such as 160, 80, 40 and 10 metres due to the ample space on these bands.

For the experienced homebrew constructor, SSB is undoubtedly the most rewarding voice mode as it's the hardest to build a transmitter for. The builder is entitled to take personally the reports of outstanding audio that accrue as the transmitter is all his own work. Also transmitting your voice (and not just dots and dashes) over 20 000 kilometres with a transmitter you built yourself is a thrill hard to describe.

A few people build digital modes transceivers. The key requirement is good frequency stability. This is possible with either a crystal or a DDS-controlled oscillator. The latter has a crystal as a frequency reference but provides often useful frequency agility. But if you're lucky you may be able to find specially cut crystals for digital mode frequencies. Unlike with CW or phone you are not at a disdadvantage as activity on each digital mode is normally confined in a 2 kHz slot and you can do the fine tuning needed via your computer.

Key digital modes to consider for QRP include WSPR, FT8 and JS8. A very simple direct conversion receiver and computer can decode their signals provided the local oscillator is stable enough. Add a few extra stages to make it a DSB transceiver. This has limitations, for instance it transmits signals on two frequencies instead of one. And the receiver may suffer from interference on the 'audio image'. However there are ways around it including using the phasing method to null out the unwanted sideband. I have done videos demonstrating homebrew digital mode receivers and transceivers. Also some kits are available if you prefer that to building from scratch.

Some top picks for QRP transmitter and transceiver projects here.

bitx

Minimum standards for homebrew rigs

The following are sensible minimum standards for any homebrew or kit QRP rig you build. My experience is that all must be followed to have successful and enjoyable results with QRP.

1. Power output at least 1-2 watts

2. At least some frequency agility in a popular part of the band

3. CW and/or DSB/SSB and/or digital modes operation.

If you see any design or kit that does not meet the above, have second thought about building it, even if it appears cheap and simple. Even if it works according to the book, you will soon become disappointed with is limitations.

Meeting the minimum standards for homebrew rigs

1. Power output

Look for a design with a reasonable power output transistor. A BFY51, 2N3053, 2N3866 or 2N4427 in the transmit final stage should have an output close to 1 watt. 2N3553, BD139, IRF510 or IRF511s are all capable of power outputs between 2 and 4 watts. Two lower power transistors can be wired in parallel (with suitable emitter resistors) to produce more output. A 2N2222, 2N3904 or BC548 as the final amplifier is a sure sign that the rig is nowhere near powerful enough.

2. Frequency agility

A free-running VFO or synthesised VFO usually provides full band coverage, but can be difficult for the newcomer to get going properly (unless you get a DDS VFO kit). It is not always easy to obtain good frequency stability in a free-running VFO on the higher HF bands, and synthesisers tend to be somewhat complex to build. Nevertheless, a free-running VFO is a good choice for an 80 metre rig provided that care is exercised in its construction.

Cheap ceramic resonators are a good choice on the lower HF bands due to their handy frequencies. A resonator for 3.58 MHz can be swung over 100kHz while a 7.2 MHz resonator can cover 200 kHz. Both tuning ranges span active portions of the voice parts of 80 and 40 metres. This makes them particularly suitable for DSB transceivers, and on 80 metres, CW rigs as well.

Quartz crystals are not recommended on 80 metres as they cannot be shifted very far in frequency. However, at 7 MHz and above, crystal oscillators (VXOs) can be pulled to provide worthwhile coverage of frequencies immediately below the crystal's nominal frequency. Ranges of 5 to 15 kilohertz can be achieved, depending on the crystal type and the operating frequency. Connecting two crystals in parallal can double pulling range. VXOs are particularly useful for CW/DSB equipment on 40, 30, 20, 17 and 15 metres. However frequency multipliers are required on 12 and 10 metres because of the inability to shift crystals very far when used in their overtone mode.

Unless you are after very low current consumption or 'bare bones' simplicity, modern DDS units are a good choice. A kit unit can simplify construction of an otherwise homebrew transceiver. They offer excellent frequency stability, a wide tuning range and (usually) a frequency offset suitable for superhet or direct conversion transceiver designs. Some are Arduino based, meaning that you can customise things like frequency ranges and tuning steps.

3. Mode

Watts are precious so it pays to use an efficient mode. Contrary to views expressed by many northern hemisphere QRPers this definition need not be confined to Morse or digital modes.

With perseverence good results are possible on SSB at QRP power levels. And DSB can be practical on QRP friendly bands such as 40 metres.

You can recognise a DSB or SSB design by the presence of a balanced modulator stage in the circuit. This is required to null out the carrier that would otherwise be transmitted (as it is on an AM signal). Devices such as the NE602 (also used in direct conversion receivers) can be used. Older designs use other ICs (CA3028 and MC1496) which are less available now. More recently there has been a swing back to two or four diode balanced mixers due to their good performance and low cost.

Like in an SSB rig, power amplifiers used in DSB rigs have to be linear. This means that a power amplifier circuit used in a CW transmitter is normally unsuitable for DSB unless its operation is made linear. Luckily the same output transistors as in CW rigs can be used but efficiency will be lower.

Digital modes have opened up a new world of transceiver design for QRP builders. For example WSPR provides an ability to set up a low power beacon that can be heard worldwide. FT8 allows 'contacts' with compromised antenna systems. And, JS8 has similarities with FT8 but has a more conversational capability. All these modes are possible with very simple DSB/direct conversion gear though SSB is preferred to lessen potential interference on both transmit and receive.

 

 

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