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K3 Review by G4AON

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Basics

The Elecraft K3 follows in the footsteps of the K2, which is a highly successful 12 Volt transceiver. The K3 is available either fully assembled, aligned and tested or as a kit comprising a set of pre-tested and aligned modules. The K3 is more desktop than backpack, measuring 10.7” wide, 10” deep and 4” high with a weight of 9 lbs with all options fitted. The K3 transmits and receives on the amateur bands from 600m to 2m (needs K144XV internal transverter module to cover 2m, needs KXV3 and KBPF3 for 500 KHz transceive), also included is 60 metres. An optional KBPF3 general coverage receive option provides receive from 490 KHz to 30 MHz, with the exception of a gap around the 8 MHz IF frequency. The K3 will only operate at very low power on 500 KHz, it gives approx. 1 mW output from the transverter interface, this can of course be increased via a suitable amplifier. In August 2009 Elecraft announced the P3 panoramic adapter for the K3, this is a stand alone adapter in a similar style case to an external loudspeaker.

Options include internal 100 Watt PA, internal auto ATU, panoramic adapter, true synchronous dual receive, 1ppm TCXO, transverter interface, internal 2m, 10 Watt transverter, digital voice recorder, external frequency standard input and a selection of roofing filters. The K3 is not supplied with a microphone, although Elecraft offer one as an option.

The K3 includes CW, SSB, AM (true double sideband),synchronous AM receive, FM and data. The basic transceiver only includes an SSB filter, in order to use AM or FM additional filters will be needed. There are front and rear panel microphone sockets, the front is configured in a similar manner to Kenwood 8 pin microphones and has a menu selectable gain range of high or low and selectable bias. The rear microphone socket is a 3.5mm jack and again can be configured for gain range and bias.

One feature that endears the K3 to contest operators is the clean synthesiser, which has up to 20 dB less noise on transmit than most other high end transceivers and can allow same site stations to operate much closer in frequency to a K3.

Unlike most amateur transceivers, line in and out sockets are included as standard. They have transformer isolation and are intended for use with a PC for data or sound recording/playback. An inbuilt decoder/encoder for CW, RTTY and PSK displays received signals in a scrolling window on the front display panel, by keying via Morse paddles, RTTY and PSK transmissions can be sent directly from the K3 without needing any additional hardware. Direct data sending and receiving appears to be possible via the RS232 serial cable, using the K3 as both transceiver and data modem.

There is a large and clear LCD display, the backlight is a soothing amber/yellow colour and can be adjusted from off to very bright. The display is easily viewed in complete darkness or full sunlight and can be also adjusted for viewing angle. There are green LED indicators for the multi-function knobs, the intensity of these LEDs can also be adjusted. The image above doesn't do justice to the LCD display and appears a little soft, one of these days I will get a really good image of my K3!

Antenna change over is via PIN diodes for completely silent operation, full break-in is provided together with semi. There are no clicks or thumps when operating full break-in, coupled with the smooth side tone CW operation is very pleasant.

Tuning via the weighted tuning knob offers three main tuning rates and two display resolutions including display resolution to 1 Hz. When RIT/XIT is not in use the RIT knob can double as a coarse tuning control for fast QSY. Friction for the tuning knob is fairly crude and relies on adjusting the knob to rub against a felt washer. Having used the same method on a K2 for six years, I've not found it to be a problem or to need adjusting.

Several useful parameters can be displayed on the VFO B area of the display, these are selected by pressing the display button and rotating the VFO B knob. Available parameters are: supply voltage and current, time in 24 hour format, date in EU or USA format, PA and front panel temperature, phased locked loop voltage and audio output voltage from the rear panel.

There is a cute “centre zero” tuning indicator which can be used on both data and CW, the tuning indicator replaces the dB over S9 part of the “S meter” indicator. I find the tuning indicator very useful for netting CW stations and far better than using a spot tuning beat frequency. Both a spot and auto netting feature are available on the K3, so users have the best of all options and no excuse for not being able to net onto a station very accurately. On RTTY, the K3 DSP filtering operates with two passbands for improved filtering. The tuning indicator shows both tones of a received RTTY signal and is easy to use.

The rear panel has one or two antenna sockets depending on whether the ATU is fitted, these antenna sockets are selectable from the front panel and are protected by static discharge resistors and gas discharge tubes.

1/4” jack sockets are provided on the rear panel for a Morse key and paddles. The internal keyer includes 8 message buffers of 250 characters each, both iambic mode A and mode B are selectable from the menu. Both of the Morse input sockets can be used simultaneously, for example you can have a contest keyer such as the K1EL Winkey connected to the hand/computer key input with a speed set on the computer of 30 wpm and also have your paddles connected to the paddle input with the K3 speed set to 20 wpm. This combination allows you to use 30 wpm for most stations in the contest but swiftly repeat your call or details at a slower speed via the paddles.

Remote control and logging are available via a conventional 9 pin RS232 connector on the rear panel, most of the Kenwood commands can be used for programs that do not include a K3 option. The contest program by N1MM can key the K3 without needing any additional hardware and uses the RTS and DTR lines to operate PTT and keying, these parameters are set in the K3 menu. To use a SteppIR antenna with the K3 it may be necessary to use a serial cable with pin 7 disconnected at the K3 end of the cable and to set the K3 menu item "PTT-KEY" to "OFF-OFF", I don't have one of these antennas but understand it can be frustrating getting one to work with a K3 on CW. There is a USB option mentioned on the Elecraft web site, this is nothing more than a USB to serial converter that can be purchased locally.

Up to 5 roofing filters can be fitted, ranging in bandwidth from 200 Hz to 13 Khz. The additional loss of narrow filters can be compensated for by increasing the IF gain, this adjustment is available via the menu.

The serial number is written in the firmware, while there probably isn't a big market in stolen K3 transceivers, it's reassuring to know the serial number may have been removed from the rear panel but can still be read from the menu.

Design features

The K3 is a double conversion transceiver with intermediate frequencies of 8.215 MHz and 15 KHz. A high level active mixer and strong post mixer amplifier contribute to a dynamic range exceeding 100 dB, even with closely spaced signals. The K3 uses high side oscillator injection on bands up to 10m and low side injection on 6m.

Modulation, demodulation and AGC is accomplished by the DSP board and operates at 15 KHz. On receive signals are digitised in a 24 bit ADC before being processed with the 32 bit floating point DSP processor. After processing another 24 bit ADC converts the signal to audio. On transmit audio is converted with a 24 bit ADC then processed by the DSP. Noise blanking is done both within the DSP and the IF and is configurable to use either DSP, IF or both.

One nice feature of the receiver is the audio effects or “AFX”, when enabled the stereo audio of the K3 gives a delayed signal to one side of the headphones which sounds like the signal originates from a loudspeaker nearby rather than the more usual “middle of your head” source when using headphones. The delay is adjustable and works on both speech and Morse.

On transmit there is a low power amplifier for output levels to 12 Watts and an optional internal high power amplifier for levels above 12 Watts. With power levels below 12 Watts, the PA is bypassed with a relay for improved efficiency.

When the high power amplifier is fitted two quiet fans mount on the rear panel to provide sufficient cooling for a 100 Watts carrier output of up to 10 minutes duration. The fans are almost inaudible even when running at full speed and make a pleasant change from the vacuum cleaner sound of many modern transceivers. PA temperature is constantly monitored by the main processor in the K3, under high temperature conditions the power output is reduced under processor control.

The synthesiser uses a combination of direct digital synthesis and a phase locked loop for low phase noise.

Both on transmit and receive there are 8 band graphic equalisers with +/- 16 dB adjustment at each frequency. There is also a noise gate parameter to shut off the microphone when not speaking, this can eliminate background noise such as computer or external amplifier fan noise.

Assembly

Most buyers will probably choose the modular kit which is a “no solder” kit requiring only a few basic hand tools to assemble. The term “no solder” isn't quite correct as the power lead uses Anderson Power Pole connectors which need to be soldered to the supplied cable, however this only takes the most basic of soldering skills and an ordinary 25 Watt iron.

My K3 comprises the 100 Watt PA, auto ATU, KXV3 transverter interface, general coverage receiver module, 1ppm TCXO, 6 KHz, 2.8 KHz, 400 Hz and 250 Hz filters (all 8 pole).

The modules, panels, instructions and various nuts, bolts and washers arrived very neatly packed in a single large cardboard box. There is no need to do a full inventory check of all the minor hardware items, although it helps to check the basic modules and panels are correctly supplied.

For assembly it is essential to provide an anti-static mat and wrist strap as most of the modules are static sensitive. Good lighting and good screwdrivers are also essential if you are to avoid a slipped screwdriver damaging surface mount components. A basic multi-meter is required to measure resistance to ground when fitting modules, a cheap digital multi-meter is more than adequate for the purpose. A 50 Watt resistive "dummy" load is needed for alignment.

The actual assembly is straightforward and well documented in a step by step manner. The only problem I encountered was mounting the front panel to the main unit which required a ten minute tea break before a second attempt, there are four multi-way sockets to mate together when fitting the panel and they are tedious to fit, however they connected correctly at the second attempt.

Assembly of the basic K3 with the auto ATU, but without the 100 Watt PA, took around 5 hours. The later addition of the PA took a further hour and involved partial dismantling of the transceiver.

Alignment

Alignment of the K3 requires no test equipment except for a 50 Ohm load rated at a minimum of 50 Watts. The alignment and calibration is straightforward and takes about an hour if done manually, or considerably less using the free K3 utility program. The transceiver should be aligned and tested as a ten Watt transceiver before adding the 100 Watt PA. The master oscillator can be easily set to frequency, unlike many other transceivers this can be done from the menu without removing panels or needing tools. The 1ppm TCXO can be improved by entering the calibration table data into the K3 via the K3 Utility program, version 1.2.9.25 or later of that program is needed, which is free from the Elecraft web site.

The first items to configure are the IF filters, these need setting for their position on the main board, bandwidth, loss and frequency offset. The configuration of the filters is mode dependant, so needs doing for every mode. The K3 utility program allows the filter parameters to be set in a matter of moments. The K3 has an automatic VCO alignment feature which takes a couple of minutes to complete. The only other alignment is the optional power meter setting followed by an automatic power gain alignment using the Elecraft utility program which will auto align the TX gain settings on each band, all you need to do is connect a dummy load! Finally the oscillator is set on frequency by setting the display to the known frequency of a reference, e.g. the 5th harmonic of a 10 MHz standard on 50 MHz. A short wave broadcast station will be accurate enough if you don't have a frequency standard. In Europe you can use the Russian RWM frequency and time transmissions on 4996 KHz, 9996 KHz and 14996 KHz. RWM transmits a plain carrier on each hour and half hour for 7 mins 55 seconds.

After initial setting up my CW 8 pole filters, it became apparent the 400 Hz filter seemed to have greater loss than the 250 Hz one. If anything the 250 Hz filter would normally have greater loss. Careful checking with a signal generator as a signal source, the filters were found to require some offset (adjust the offset in the menu while observing the S-meter on a signal around S5, set the offset in the centre of each point where the signal level drops one S-meter "block"). The 400 Hz 8 pole filter now has a menu offset of -0.07 and the 250 Hz an offset of -0.05.

Use

The K3 may take a little getting used to, needing a few references to the manual. Basic operation is straightforward. There can be problems such as not being aware that unless the “Tech mode” is set to “ON” in the menu, some of the extra display items are not displayed on the front panel. The K3 can be driven by the buttons and rotary controls on the front panel without needing to use the menu, except for infrequently used items such as the equalisers. Some features in the manual may not currently be implemented in firmware, however the latest situation on firmware features can be found by looking on the Elecraft web site for the "owner's manual errata" which is often a better source of information than the brief notes included with the firmware updates.

There are no signs of holes being made in the received audio by AGC overshoot from noise pulses as has been reported with other DSP IF transceivers. There is a parameter in the menu for AGC pulse suppression that needs to be set to "nor" (normal) otherwise the receiver momentarily dies every time someone turns a light on in the house.

Various users have reported the receiver in the K3 as sounding hard and fatiguing to listen to for any length of time. Under wide band "hash", or high summertime static conditions, listening to SSB can sound harsh compared to some receivers. Moving the IF shift control to give a centre frequency of 1.3 KHz instead of the normal 1.5 KHz gives a warmer sound to receive audio without needing to fiddle with the receive equaliser...

Synchronous AM works quite well, it needs the 6 KHz "AM" bandwidth filter and operates in a similar manner to extended SSB receive and switches between upper and lower sideband by rotating the SHIFT control. Music transmissions on AM broadcast stations sound natural, however some broadcast stations appear to transmit low frequency data which can be heard with a K3 due to the extended frequency response, this can be reduced by decreasing bandwidth but currently with f/w 3.58 it isn't possible to adjust the LF side of the passband as SHIFT just switches between USB and LSB. The K3 auto tracks/locks up to 2.5 KHz and will work with sync AM on amateur "round table" nets, when used like this the K3 needs to be used in "split" mode otherwise your own transmission will jump around (listen on VFO A, transmit on VFO B).

Transmit signal reports were excellent with no reported issues. The internal keyer works very well, although I appreciate that many prefer their own external keyer. Almost any microphone can be used with the K3, especially if the TX equaliser is carefully adjusted. See microphone choices further down the page for specific information.

6m on the K3 is not the best implementation around, the sensitivity is less than many other transceivers which prompted Elecraft to introduce an external pre-amplifier. The low frequency IF and low side oscillator injection give less than ideal image rejection figures, I could only obtain an image rejection figure of 62 dB on 6m, which is below the specification of 70 dB. Also on 6m there are several low level birdies that sweep through the passband as you tune, there is a "work around" in the firmware to minimise these but it would be preferable if they weren't there to start with.

I have operated with the K3 in several CW contests, using mainly 40 metres during the dark evenings with an Acom 1000 linear and quarter wave vertical antenna. Overloading of the receiver was never an issue and comparisons against other transceivers, including a K2, gave the K3 a clear receive advantage.

Most linear amplifiers require no special configuration settings or additional interfaces, connection being nothing more than a single screened phono lead and a PL259 lead for the RF. There is an ALC input to the K3, but it's use is not recommended. Older linear amplifiers will probably need an external relay to isolate their high Voltage keying and some may change over too slowly for the maximum 20 mS switching time catered for by the K3 menu. There are still hopelessly slow switching linear amplifiers on the market which should be avoided like the plague. The K3 TUNE button can be configured to output any preset RF level from 0.1 to 110 Watts for amplifier or ATU tuning purposes (or the normal power level as set on the "PWR" control), this makes amplifier tuning a breeze. Full QSK is no problem with the K3 and an Acom 1000 linear.

The K3 really works well on data modes used via sound cards, I've tested RTTY with hard wired connections to the 15 pin aux socket using MMTTY (single transistor interface from the MMTTY help files) and also on PSK31, Olivia and MFSK via FLDigi. On audio FSK data modes used via FLDigi the only connections needed are a pair of stereo 3.5mm plug to plug screened leads between your K3 and PC sound card, the isolated line input/output sockets on a K3 really make for easy connections - especially with software such as FLDigi which key the K3 via the RS232 lead as well as displaying the actual frequency of PSK31, Olivia, RTTY and MFSK signals. On mode "FSK D", in addition to being able to externally key the transceiver in the conventional manner, the Morse paddles can also be used for "PC free" RTTY operation.. this takes a little getting used to and seems pointless, but does work.

Contrary to a myth circulated by the "buy my interface" people, a K3 does not need any kind of additional interface to use sound card modes with a PC, ordinary cables such as a RS232 cable and a pair of audio cables from Maplin or similar vendors is all you need. Programs such as FLDigi are "K3 aware" and key the radio via serial command and it's free software too.

Amtor and Pactor work well with a K3. The recommended settings that work well with an SCS PTC-IIex modem on both Amtor and Pactor I/II/III are:

Mode "Data A" (USB), rear panel line sockets. PTT RLS 12 mS, synchronous mode enabled (-s displayed).

The modem should be set for a TX delay of 20 or 25 mS. Typical throughput using Pactor III reaches 3200 bps with few retries.

Operating on RTTY and PSK31, which involves the transmitter operating at a 100% duty cycle, doesn't seem to cause excessive heating of the K3 PA. The cooling fans only run for a short time after returning to receive and only sound to be running at a very quiet quarter or half speed. Being able to monitor the PA temperature via the front panel is very useful and reassuring.

On some transceivers it is possible to rotate a knob and listen on each stored memory frequency in turn, or indeed scan selected memories. The K3 with later firmware (3.36 onwards) offers basic memory switching via the VFO knob and the ability to listen to each as the knob is turned. It is not as good as old Kenwood transceivers (TS570 and 480) which have much more sophisticated memory features.

With the KXV3 transverter interface, the antenna feed can be looped via an external filter or pre-amplifier. I have connected an external antenna splitter to mine, the RX antenna out feeds the input of the antenna splitter, one port of the splitter connects to the RX antenna in, the other to an external receiver. I use a Perseus SDR receiver to give a panoramic display and also to work as a 2nd receiver. I can synchronise the K3 to the Perseus (or vice versa) using Ham Radio Deluxe (HRD). The combination of HRD and the K3/Perseus work perfectly together, both have good frequency accuracy for near perfect matching of frequencies making it very easy to "click and go" with the Perseus and have the K3 jump to the same frequency. While I haven't compared the Perseus to any other SDR such as Softrock or LP-Pan, the very high performance of Perseus is not easily matched. The circuit and measured performance of the splitter are shown below.

Microphone and headphone choices

Unlike most other transceivers, the K3 can accommodate almost any microphone. Some of the cheapest are the best, and some of the more expensive are a waste of money as far as using them on a K3. The Elecraft supplied microphone and headsets offer no advantage over buying lower cost alternatives locally and indeed you may find spare microphones or headsets in the shack which work better.

The best hand microphone is the low cost Kenwood MC-43S as used on the TS-570 and similar transceivers. As at mid June 2012 these are still available from Kenwood dealers (£20.95 from Waters and Stanton in the UK). Even without any transmit equalisation these microphones often sound exceptional on a K3. The only downside is the press to talk lever sometimes "creaks" unless you are careful to not move your thumb while speaking into it.

Computer headsets, especially the more comfortable "gaming" variety often produce really good audio on transmit, I have heard several stations using them and the price in most cases was less then 15 pounds. Heil headsets with the HC-5 insert also sound quite good.

Filter choices

There are basically two main types of roofing filters for the K3, the 5 pole ones by Elecraft and 8 pole ones made for Elecraft by Inrad. I decided from the outset that if I bought the 5 pole types I would eventually replace them with the slightly more expensive 8 pole ones. As the percentage difference in the final cost of a K3 fitted with 5 pole as opposed to 8 pole filters was so small, I didn't even consider the 5 pole types. Most of the time I operate CW in relatively uncrowded, but noisy, parts of the lower frequency bands. The noise is wideband atmospheric and similar "hash" which benefits from narrow filtering. For a long time I operated CW with a 400 Hz filter but usually with the DSP bandwidth set around 150 ~ 300 Hz, eventually I bought a 250 Hz filter and now find it to be my filter of choice for CW operating, it doesn't have additional loss compared to my 400 Hz filter and so there is no disadvantage in using it.

For those using, or contemplating, a second receiver option for the K3 should note that any 5 pole filters must be matched in frequency offset in order to provide proper diversity receive without signals sounding strange. The 8 pole filters are of close enough tolerance to not need offset matching. The ARRL review of the K3, available from the Elecraft web site, covers filter choice too.

Noise reduction (NR)

The subject of how well, or how poorly, the noise reduction in the K3 works has been the subject of much debate on the Elecraft Reflector. Prior to firmware 3.25 (released in mid August 2009) the noise reduction could best be described as poor. However the later firmware provides effective noise reduction which is as good as any other, it is especially useful against wideband summertime "hash" on the lower bands such as 80m. It seems to work better on SSB than on CW, this may be the result of using wider bandwidth on SSB and noise reduction being more effective in wider bandwidths. The auto and manual notch filtering is quite good. The noise blanker has not been tested as I don't suffer from impulse noise and don't have a pulse generator.

AGC

Several users have complained that under "pile up" conditions, the K3 has gone quiet and not delivered signals. Not what you would expect... There has been a beta release of firmware in May 2012 (version 4.51) to address this problem, which it seems to accomplish.

Firmware updating

Some transceivers may appear difficult to update their firmware, indeed some may require returning to the dealer if the firmware update fouls up. Fortunately, the K3 is very robust in that regard and can be recovered easily even if the laptop battery goes flat during an update. The only cable required is a standard RS232 cable available in the high street shops.

There are free "updater" programs available for Microsoft Windows, Macintosh and Linux. The program connects via ftp to the Internet and automatically downloads the latest firmware version to the computer, or in the case of beta versions you have to manually download the "Zip" files to a directory of your choice and extract their contents. Updates were released every couple of weeks in the early days and have fortunately reduced as the K3 has matured. The configuration of the K3 can also be saved to your PC for later re-loading, however, it is not necessary to save and reload the configuration when updating firmware.

Purchasing

The K3 can be purchased in the UK from Waters and Stanton or directly from Elecraft in the USA. Prices from Waters and Stanton are higher than ordering directly if you compare them against the lowest cost delivery option of US Postal Service. However, compared to delivery by UPS Worldwide Express (the fasted but most expensive delivery option from the USA), the prices are almost exactly the same and include a 2 year warranty if bought from W&S.

Direct orders from the USA ship in a couple of days from placing your order and can arrive at your door as soon as 3 days from dispatch when using the more expensive UPS delivery option, or up to 3 weeks later if using the much cheaper US Postal Service. The K3 ordered directly from the USA will be subject to a handling charge by either UPS or ParcelForce - US PS hand over to ParcelForce on arrival in the UK. Handling charges are typically £11 for UPS and either £8.50 or £13.50 for ParcelForce, plus vat at the current rate (20%) which is payable before delivery. There is no duty charged on imports of the K3 in the UK.

Full details of price: http://www.elecraft.com/

Measurements

While I have quite a few items of test equipment, much of it is not officially calibrated and therefore it is not appropriate to be too specific on measurements in many areas. I do have a very accurate GPS derived frequency standard, a calibrated power meter which is better than 5% from 160 to 6m and a calibrated spectrum analyser. My signal generator is reasonably accurate in comparison with the calibrated spectrum analyser, but cannot be confirmed accurate at low signal levels as the analyser will only measure down to around - 90 dBm.

Receive figures are:

The performance using the KBPF3 general coverage receive module hasn't been thoroughly tested, however sensitivity below 1 MHz drops off and is roughly 20 dB less sensitive at 500 KHz than at 1.9 MHz when measured via the main antenna socket(s), there is no drop off if measured via the KXV3 transverter interface. The image rejection when using the KBPF3 is around 8 ~ 10 dB worse outside the amateur bands, the performance within the amateur bands is within specification.

The sensitivity on 50 MHz has been the subject of some debate on the Elecraft Reflector and Elecraft now offer the PR6 external pre-amp to improve the sensitivity. By comparison, my Kenwood TS-480SAT is 8 dBm more sensitive on 50 MHz than a "non pre-amp" K3. Note -126 dBm equals a level of 0.112 uV pd. Whether the above sensitivity makes much difference in the real world may be academic, it depends on your local noise levels. The image rejection figure I measured is some 8 dB below published specification and also a similar amount below the figures measured by others, a re-alignment of the bandpass filters on 6m didn't make any difference to the image rejection or sensitivity figures. Adding a 0.5 dB noise figure external pre-amplifier between the RF out and RF in of a KXV3 interface improved the sensitivity by 10 dBm giving 10 dB SINAD at -136 dBm in 400 Hz bandwidth and a MDS of -146 dBm -which compares to an MDS of -136 dBm without the pre-amp. The pre-amp I am using is an Advanced Receiver Research Inc. model P50VDG (http://www.advancedreceiver.com/) with power derived from the +12 Volt output of the K3. There is no need to add a 10 dB attenuator after the pre-amp as the K3 attenuator works fine to reduce strong signals and in any event the pre-amp can be switched out by pressing the "RX ANT" switch on the K3.

The K3 would normally be calibrated for an S9 signal with an input of 50 uV with the pre-amplifier turned on. As most of my operating is on 80m and 40m where I don't use the pre-amplifier, I set the S-meter for 50 uV without the pre-amplifier. There are easy to use menu settings for S-meter calibration. Above S9, the S-meter tracked signal level increases remarkably. In dBm levels 50 uV = -73 dBm, an input of -53 dBm read S9 +20 dB, -33 dBm indicated S9 + 40dB and -13 dBm indicated S9 + 60 dB. Below S9 the accuracy dropped slightly but was still close to 6 dB/S unit. The results (which in reality are not important) are significantly better than any other S meter I've tested. The S meter can be configured to show the same reading regardless of the pre-amp or attenuator being selected.

Two tone dynamic range testing was only possible on 14 MHz as I only have one signal generator, the other being a well buffered 14 MHz fixed crystal oscillator based on the design for dynamic range testing from the book "Solid state design for the radio amateur". Both these were combined in a hybrid coupler and fed via a variable attenuator to the K3. The factory figures give a 100 dB dynamic range at 5 KHz spacing and 95 dB for a 2 KHz spacing, both using a 400 Hz (8 pole) filter. My measurements give a two tone dynamic range at 2 KHz signal spacing of 100dB with the pre-amp off. These figures are for a 400 Hz bandwidth with the 8 pole 400 Hz roofing filter, similar high dynamic range figures exceeding 100 dB at close signal spacing were also obtained by the ARRL (review in April 2008 QST), two other amateurs and also by Rob Sherwood the well known receiver tester, these tests were independent of each other and on different K3s.

At 100 Watts the power output measured on several bands was lower than expected. The figures at the 5 Watt and 50 Watt calibration levels are very close to the indicated power, the 100 Watt level may be something later firmware could address by including a third calibration level. The lower power output at 28 MHz may be due to the SWR meter indicating reflected power on that band which is something internal to the K3, I've not investigated the matter further at this point.

There were no high power peaks when transmitting on low power CW and the waveform of CW transmissions were smooth and clean. The synthesiser in the K3 is much cleaner than most transceivers, ARRL measurements show the transmitted noise to be around 20 dB less than other top flight transceivers. See the various ARRL reviews of "Spectral display of the xxxxx transmitter output during composite noise testing" and you will see how significantly cleaner the K3 is compared to most of the other transceivers. The reason you can hear your neighbouring amateur keying away at +/- 50 KHz is generally due to their transmitter outputting high levels of synthesiser noise, a 20 to 30 dB reduction would be very welcome! My measurements show the noise floor to be 100 dB down on peak output +/- 5 KHz from the carrier on CW at 50 wpm and at any power level. Click here for an image of the close in spectrum when keying at 50 WPM, 100 Watts output.

Change over times for ARQ modes are approximately 20 mS when using the "Synchronous data mode". This timing is suitable for use on Amtor and Pactor modes.

Power output when operating at low Voltage was also tested. For a supply of 11 Volts measured at the power supply with a power level set at the K3 of 100 Watts, an output power of 85 Watts was measured on the 20m band. At 5 and 50 Watts the power output closely matched the set power on the K3. Operating from batteries should not be an issue with a K3.

The frequency of a K3 fitted with the optional TCXO can be set to within 1 or 2 Hz at 50 MHz. Frequency accuracy was maintained to better than +/-20 Hz at 50 MHz when the transceiver was either warm or cold. The frequency accuracy/stability shown above was obtained with the optional 1ppm TCXO.

The spectral purity within all the amateur bands was within specification, however on 5 MHz the spurious levels failed to reach specification when transmitting below the current lower band limit and was approx -46 dBc at 5.151 MHz.

Two tone 3rd order IMD products are typical of a 12 Volt solid state PA and are of the order of - 30 dB at 100 Watts output, improving by around 10 dB when running at quarter power.

Conclusion

The K3 represents one of the finest transceivers available, and at a lower price than many competing transceivers. It caters for casual operators, contest operators and QRP enthusiasts with genuinely high performance for code and speech modes. The low noise transmissions are particularly neighbour friendly and are a great asset in multi-operator stations, even allowing DXPeditions to operate CW and SSB simultaneously in the same band. Performance on 6m is less than ideal due to the presence of several low level spurious signals, the low sensitivity on six can be overcome with a pre-amp.

Regardless of minor irritations, the K3 is still about as good as it gets for an Amateur HF transceiver and has greater two tone dynamic range on receive than most other transceivers at 2 KHz signal spacing. Rob Sherwood (Sherwood Engineering) currently puts the K3 3rd on his list - http://www.sherweng.com/table.html

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