®®Last updated Sept. 28, 2008 2345 UTC
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K3 Rear I/O Details
The receiver signal flow is as follows.
Incoming RF passes through the TX low pass filters, the T-R switch and to a bank of relay-switched bandpass filters.
Next is a switchable (by relay) 10 dB attenuator followed by a switchable (by relay) high-performance RF preamp.
A unique switching mixer design then accepts the RF signal along with the output from the DDS-steered, PLL-based synthesizer. The synthesizer design took months of effort to create to achieve extremely low phase noise along with fast frequency slewing and stay-on-target for costs.
The mixer post-amp is a high-standing current design which feeds the noise blanker and the IF output buffer amp.
The K3 uses an IF of 8.215 MHz. There is no up conversion involved. At 8.215 MHz we can create high-performance roofing filters for outstanding selectivity before the DSP gets involved.
In fact, the filters are so good that we can go from there directly to the DSP IF of 15 kHz without any intervening 455 kHz IF section. This improves performance -- and lowers costs -- by requiring fewer mixers that can overload and oscillators that contribute phase noise.
The crystal filter (up to five, and up to three of them can be variable-width, another unique K3 feature), feeds an FET IF amplifier which is also AGC controlled.
Next is a second mixer with injection derived from the synthesizer reference oscillator. The output from the mixer is differentially amplified at the 15 kHz IF and fed to the DSP.
There is also a peak detector circuit here which activates at high signal levels to protect the analog-to-digital converter from over- ranging.
At this point, the DSP takes over, accepting the differential 15 kHz IF signal and performing conversion to audio, IF and AF filtering, and myriad other signal processing tasks.
On transmit, the reverse path is taken. Again, there is no intermediate 455 kHz IF stage required. The 15 kHz IF signal is directly converted to 8.215 MHz and then to the desired operating frequency.
A FET-based 10 watt PA (capable of 20 watts in most cases) is used as the output amplifier in the QRP version, and as the driver for the 100W PA in the QRO version.
Initial results indicate the K3 exceeds the K2 in every respect, and most of the specifications of those large, heavy other-brand rigs, too. For the ARRL and Sherwood Test Results see: http://www.elecraft.com/K2_perf.htm
Would the K3 be any less susceptible to 60 Hz hum influences from large sources and ESD failures when an antenna is connected during these incidents compared to our K2?
The K3 includes ESD/lightning protection on all antenna jacks. It will outperform the K2 in terms of 60-Hz hum susceptibility.
Can the K3 be "muted"? If so, is it done via the accessory connector on the rear panel?
PTT switch closure puts it into MUTE mode. You can also do this with a PC command. At present there's no dedicated MUTE-only input, but we could add that if there were a good use for it.
What is the loss through the roofing filters and is it compensated for?
Like other roofing filters, the narrower the passband, the more loss. In general the loss is similar to those shown for the FT-1000 8.215 MHz filters shown on the INRAD web site. Our 5 pole filters in some cases have a little less loss. The loss at this point in the radio (the first IF) has very little impact on MDS or other characteristics, because the noise figure is established in earlier stages.
When you install any roofing filter, you use the menu to tell the firmware what the filter's bandwidth is, any small offset from 8.215 MHz, and what the relative loss of the filter is. The DSP adjusts the 15-kHz IF gain based on the entered loss amount, so all filters have the same overall gain.
Once a filter is installed, you can specify which modes it is available in (or all modes).
How many DSP filters are there?
They're calculated instantly, on demand, so essentially they're unlimited. If you wanted to put a number on it, I'd say 500-1000. But you never have to think of it in those terms; simply adjust the WIDTH, SHIFT, HI-CUT or LO-CUT controls as required.
Are they mode dependent in their selection, or are they selectable independent of mode?
DSP settings are stored per-mode and per-preset. Crystal filters are selected either automatically as you adjust the DSP settings, or manually by tapping XFIL.
Are they adjustable by a single control or are they set using a fixed filter, and using shift controls to change the setting?
We use two knobs that have two functions each. You can treat the knobs as SHIFT and WIDTH, or LO-CUT and HI-CUT, easily toggling between the two representations. The LCD's DSP filter graphic, centered directly between the controls, shows you instantly how you have the passband configured.
What is the frequency variance per filter?
We could set this up as the operator prefers, but at present we're using 50 Hz per step, which provides quite adequate resolution. At 10 Hz it can take too long to change the passband.
How are the RIT and XIT controls used and what are the LEDs for?
When RIT is ON, it is applied to the VFO A display. You can also see the amount of offset as you turn the RIT control (+/- 9.99, shown on the VFO B display). You can check the amount of offset without adjusting the control by holding the DISP OFS switch (below XIT). RIT steps can be set to 1 Hz, 10 Hz, or 50 Hz by holding the RATE switch (below RIT).
If you have RIT or XIT ON, and the offset control is not set at dead center, the yellow LEDs will tell you whether you have a negative or positive offset. When RIT and XIT are both off, the offset control advances VFO A in large steps, defined by the operator on a per-mode basis (e.g. 2.5 kHz for SSB, 5/9/10 kHz for AM, etc.).
How effective is the noise blanker on the K3?
The noise blanker has been totally redesigned and is being tested on a wide variety of noise sources. We studied several different design approaches before starting the KNB3, including the Drake circuit. It is also supplemented by DSP noise blanking, which will work in some situations that would defy IF blanking. The two in combination (not to mention DSP random noise reduction) will really shine.
How does the Noise Reduction work?
NR depends on correlation of the
present input with previous input. The system does not actually provide
Noise Reduction; it provides Signal Selection. In other words, its default
is to pass nothing at all. It has to believe there is a signal present, and
then it builds a filter, or set of filters, around the spectral components
of the signal it thinks is there.
Random noise has no correlation, voice has moderate but not perfect (unless
you whistle a pure tone) and CW has excellent correlation. As a
result, noise is heavily suppressed (no filter is built to pass it), voice
is partially suppressed (hence it needs some additional gain to compensate
for this effect so the same AF level will produce about the same audio level
with a moderate S/N speech signal) and CW is hardly suppressed at all (hence
it does not need any gain boost).
NR is not recommended in Data Mode. Data is already getting a matched
filter in the demodulator. You might lose a few symbols as the NR settles
around the signal, and it might suppress a very weak signal that you could
otherwise copy.
NR in the end is intended for modes you listen to.
Yes. The DSP works in conjunction with hardware AGC to smoothly handle signals like this. In addition the K3's hardware noise blanker would remove such "pops" when enabled. It has a variable threshold, so you could leave it on and set for a high threshold if random pops were an issue on a given band.
Does the AGC toggle between two, or more settings?
Fast or Slow (indicated by AGC-F or AGC-S icons).
Are the settings variable in terms of attack, hang, and decay?
In the menu, you can set the following parameters for AGC: Pulse (noise pulse rejection), Hold (Hang) time, Decay (in dB/sec for Fast and Slow), Threshold, and Slope. Slope sets the compression you get from AGC, whether you like everything above the threshold to be flat (S4 and 40 over S9 are the same level) or some sort of slope (2:1, 10:1 whatever) so stronger signals are somewhat louder.
Will they be mode sensitive?
Not currently. Slow and Fast covers most cases. Settings are saved per operating mode.
What frequency range will the general coverage (GC) receiver have?
0.5 to 30.0 MHz.
With a first IF of around 8 MHz, how can the receiver be general coverage? Will there not at least be hole in the coverage around the IF frequency?
General does not mean continuous in this case. There is a small gap at 8.215 MHz. You may be able to tune to this frequency, or not, depending on the firmware. There is a trap circuit to suppress response at this frequency, so the receiver won't work very well within several kHz of 8.215 MHz if it does allow you to tune there.
Will the K3 be able to tune WWV without the general coverage filter option?
Yes.
The K3 performs very well as a SW broadcast RX. The DSP IF and AF have very low distortion, and you can adjust the passband with our 8-band RX EQ. We have plans to add synchronous AM detection as a future DSP firmware upgrade.
Is there anything special about how the K3's dual VFOs work?
There are dual VFOs (A and B), controlled by separate VFO knobs. You can operate SPLIT, as usual, whether there's a subreceiver or not. The K3's VFOs can be set to different modes and even different bands. Each VFO also keeps track of its own filter presets (I and II), on a per-mode basis. A "preset" in K3-land is a combination of a crystal filter (selected automatically by the DSP controls) and the DSP settings (SHIFT/WIDTH or HI-CUT/LO-CUT, which can be used interchangeably). Having two presets per-mode/per-VFO allows you to set up the two XFIL/DSP combinations you use most often and quickly toggle between them using the I/II button.
There will be an option to link the VFOs (frequency and/or mode and/or band), or make them fully independent. For example, if you allow VFO B to be completely independent of A, you can set it to a different band, perhaps to monitor a calling frequency, while using VFO A for normal ham-band RX/TX.
VFO B has its own frequency display, LOCK icon, and (if the sub is installed), its own AF GAIN control. To set up other VFO B/subreceiver parameters, you can either set up VFO A first and swap it with B, set up VFO A and copy it to B, or use the BSET switch to directly set up all VFO B parameters. When BSET is in effect, all of the DSP controls, S-meter, etc. pertain to VFO B/sub.
Of course an external computer control program could present two entire sets of controls, S-meter, etc. for the two receivers. This is left as an exercise for the reader :)
Is the K3 capable of dual receive with just VFO A and B ?
No. You need the subreceiver option to hear two signals at once.
Please consider providing these 3 functions, especially useful for stereo diversity reception:
1. Option for the subreceiver settings (mode, BW, PBT/shift, AGC) as well as the VFO to automatically track the main receiver settings. AF/RF gain would remain independent.
These are already either supported or on the list.
2. Option for RIT to change both the main RX and sub RX frequency.
Added to the future feature list.
3. Single button press that would "push the context" of the main receiver to the subreceiver if the receivers are otherwise acting independently.
Already present. There's also a menu function B>A to push VFO B settings to VFO A. This is something you can store to one of the programmable PFx buttons.
Is the K3's S-meter calibrated, or is there some provision for storing an S-meter calibration table?
There are S-meter ZERO and SCALE menu entries, although the default settings will usually result in 50 microvolts = "S9", the most widely-accepted standard. Whether the S-meter compensates for the preamp and attenuator is an interesting subject. We support both modes of operation, selectable via a menu option.
How does the K3 passband tuning work?
The K3 includes passband tuning. It's designed to take maximum advantage of its large number of crystal roofing filters and IF DSP in combination. There are two sets of controls: SHIFT/width, and hi-cut/lo-cut. Tapping a single button switches between the two. An optimized DSP graphic on the LCD sits just above the knobs, and shows you at a glance whether the passband has been shifted or narrowed as a result of using these controls.
The most appropriate roofing filter is selected automatically as these controls are rotated. If you have one of our [pending] variable-passband crystal roofing filters installed, then the 1st IF bandwidth (crystal filter) will closely track the 2nd IF bandwidth (DSP). This is far superior to receivers that have only wide roofing filters and try to do the whole job at the DSP, as well as receivers that simply shift one filter against another at two different IFs.
While similar in function, Elecraft refers to this function as Per-Band-Memories. The M1-M4 memories will work on a per-band basis allowing the user to store his favorite 4 band segments for each band and include mode, filter and tuning rate settings in addition to the frequency. In addition, memories 01-09 (not per band) can be recalled without the leading zero, eliminating an extra button press. Tapping M>V and #1-9 will get you to that memory location. Great for quick access to your favorite band.
Each
memory holds
VFO
A and B frequencies, modes, and filter settings, and can have a text label of up
to 5 characters. Memories 01-04 are Quick
Memories,
accessible with just two switch presses. To store / recall Quick
Memories
(01
– 04), tap
V
M
or
M
V
,
then tap
M1
-
M4
. The memory number and label will flash briefly.
Are they saved across power cycling?
Yes, stored in flash.
How many memories are there altogether?
There are 100 general purpose memories in addition to the 4 Quick Memories per band. That's a total of 144 memories!
How do the DSP filter controls work? (upper two knobs to the left of the main tuning knob)
Each DSP control has an integral pushbutton switch. Tapping the control alternates between its two primary functions, for example HI-CUT and WIDTH. This is reflected by the two LEDs above each control. Holding a control activates its secondary function -- NORM or I/II.
Holding NORM matches the DSP bandwidth to the crystal IF filter. It also removes any SHIFT offset.
Each operating mode provides two filter presets, I and II, which store crystal filter selections and DSP settings. Hold I/II to alternate between them. This is very useful if you have preferred narrow and wide DSP/crystal filter setups for each mode.
What are the K3's binaural effects?
The K3 AFX (audio effects) creates the illusion of added space, similar to stereo, and has user adjustable settings. The binaural mode is similar to binaural I-Q (please see March 99 QST).
Please elaborate/detail the Advanced Noise Reduction.
LMS algorithm-based denoiser and autonotch.
All antenna ports have gas-discharge tubes, and the RX-only ports also have carrier-operated relays.
We also monitor the SWR bridge in receive mode (forward/reflected power). If a signal large enough to cause front-end damage appears in the main T-R path (a "reverse transmit" condition), we quickly open the PIN diode path to the receiver, typically in less than 1 ms. The path will recover equally fast when the huge external signal disappears. Obviously this situation is to be avoided, which is why such stations often use external band-pass filters.
At a certain power level the RX path will be opened (and the audio muted) to avoid exposing the preamp, mixer, and down-stream stages to multi-watt signals.
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QRP operations - How low is low?
Power levels can go down to 100 mW even with the 100-W option installed. If you have the RF I/O option (the KXV3), which has the transverter interface, you can adjust power output from about -15 to +3 dBm (about 2 milliwatts!). Just connect your antenna to the transverter jack.
How does the DSP IF speech processor compare to a true RF processor?
The K3 RF processor works at IF. Essentially you create an SSB signal, using AGC/compression to keep the average signal level reasonably constant. You then apply additional gain to the IF SSB signal which drives the clipper. This gives you "RF clipping" with an adjustable amount of clipping. You then re-filter the resulting signal and convert it to the output frequency. Thus, the K3 has a true RF speech processor. It also has audio compression ("ALC") and an 8-band TX EQ to tailor the overall response.
The K3
will be capable of ESSB, with an upper passband of around 4 kHz, provided the optional 6 kHz
filter is installed.
12/3/07: ESSB is not yet enabled. Firmware will be released soon to
enable this feature via download from the software page.
What filters are used in determining TX bandwidth?
Only the filters on the MAIN RX board are used during transmit. Filters on the subreceiver have no effect during transmit.
The KAT3 is internal and very tightly coupled to the 10-W or 100-W stage.
While you could in theory interpose an external amplifier between the 10-W stage
and the KAT3, we haven't tried it, and it would require special firmware
support. I really wouldn't recommend this. The KPA3 is a high-performance 160-6m 100-W
module with excellent heat sinking, monitoring circuitry, two fans, and its own
circuit breaker. This results in very smooth high-power operation, while an
ad-hoc solution external to the radio might not.
We also don't plan to support the KAT100, for [very good] reasons I outlined in
my earlier posting on the auxbus.
If I purchase the K3 10W version is there an open space in the rear of the case where the KPA3 with fans would go; or are the Fans an integral part of the case regardless of the power version?
The fans and 20A breaker come with the KPA3 option. The 10-W stage uses a large portion of the bottom cover as its heatsink, like the K2. This works quite well.
Will the K3 have a low-power TUN setting for adjusting amplifiers or external manual tuners?
Yes. This can be set up in the K3 menu.
Does the standard K3 include 60m transceive (or maybe it is limited to the USA channels?).
The K3 includes 60 meters and works on most international 60M allocations. (Some minor retuning of the 60M bandpass filters may be required for some international 60M bands.)
Operation down to 500 kHz does present challenges. The K3's receiver sensitivity drops quickly as you tune below the AM broadcast band. We'll post performance numbers for the low range when we have them. At present there is no way to transmit below 1.8 MHz. However, it is possible that we could provide a special band-pass filter array, since the the KBPF3 is a plug-in module. This has been added this to the future features discussion list.
The K2 has an 8-bit DAC. The K3's DAC has more than 16 bits. You'll never see the power jump! The SWR/power bridge is also built-in, so you'll have it without or without the KAT3 option. The knob is a shaft encoder, without detents, but it's very easy to dial in the power you like. You could also assign one of the programmable function buttons to turn the PA on/off.
What is the microphone pin-out on the K3?
The K3 8-pin microphone connector is wired the same as the K2, which is generally compatible with the Kenwood dynamic microphone pin-out. Plus we added a lot more mic pre-amp gain (adjustable) in the K3. There's also a 1/8-inch mono mic connector on the rear panel which can also be directly used with Heil headset microphones like our Proset-K2. . This helps with keeping the clutter down during the heat of a contest. The mic source is set from a menu option. Diagram
Immediately after a band change, how long do you have to transmit in order to get 100W output?
Transmit gain constants are stored each time you adjust power. If you change bands and hit the key, power will come up instantly to the previous level, unless the SWR changed drastically.
Does the KPA3 have plenty of power to allow for 100-W full duty cycle operation in all modes?
We may limit power level or maximum TX time for 100% duty-cycle modes (AM/FM/FSK). I can't say for certain, because we're still doing extended transmit tests. We used two fairly large, standard-size fans so they'd run at slow speed in most operating situations. But fans in this size are readily available with higher CFM ratings, so we could offer an extended-duty-cycle upgrade if that were warranted. This would only increase the depth of the fans; you wouldn't have to add fans to the top of the cabinet.
The fans have 4 speeds, are temperature controlled, and they turn off when not needed. They're large and quiet.
In fact the entire fan panel is an upgradeable module -- we wanted to make sure the K3 could adapt to specialized requirements.
So far our feedback from RTTY contesters is that they were able to operate a whole contest without getting the K3's heatsink too hot. The fans rarely went to full speed.
Will the K3 have a menu setting for "carrier offset" or something equivalent?
Shifting the IF in relation to the crystal filter during TX mode in order to may be a feature included in a future firmware release.
In TX, the S-meter bargraph breaks into two segments; SWR and RF output. In SSB, it can optionally display ALC and compression.
In addition to the SWR bargraph, which is available at all times when transmitting, the SWR is shown numerically on the VFO A display during TUNE (up to 99.9:1). Power in watts is shown on the VFO B display. The only time SWR is not shown during TUNE is when you're using the 0-dBm transverter I/O (on the KXV3 module). In this case, we assume that the device you're driving (a transverter) has low enough SWR. The VFO A display shows the power level in dBm, and VFO B shows the power in milliwatts (with .01 mW resolution). The transverter's power output detector can be calibrated using a menu entry, as can the RF detector in the main RF path.
SSB Power control and ALC metering
MIC GAIN SETTING: Adjust MIC gain for an ALC meter peak at around 5 to 7 bars during normal speech (rev. D owner's manual, page 28). This applies even to TX TEST mode, meaning you can set it off-air. This indication does not mean that you're "hitting the ALC really hard." When you get to around 5 bars, you'll be "tickling" the DSP's ALC. More on this below.
ALC METERING: The K3's ALC meter is a bar graph, not an analog meter, and we felt that 5 bars would provide the right granularity at the target ALC level. The 5th bar of the ALC scale is heavier than the others, serving as a reminder of the this level.
ALC DESIGN GOAL: The K3 was designed to minimize transmit splatter and other effects that plague some rigs. To achieve this, we apply all ALC before the crystal filter, and minimize the application of ALC in general. The levels have been carefully calibrated to that 5-to-7-bar level mentioned above. The result is that the crystal and DSP filters remove the types of artifacts that in many other rigs end up as transmitted wideband noise or clicks. I believe this is why we continue to hear excellent reports from K3 users regarding their on-the-air SSB signals. (We've also heard, from some experts in the subject, that the K3's compression is among the most effective they've ever measured.)
PER-BAND POWER CONTROL: With some vocalizations, speech energy may build up within a narrow crystal filter to produce a slight peaking effect. Because of this, the user must set the K3's power output level such that it peaks at or below the safe level for any external amplifier under all speech conditions. To facilitate this, you can use per-band power control (refer to the PWR SET configuration menu entry). We have many customers using this method. It compensates for per-band gain variation in the external amp or the K3 itself, again reducing the need for ALC. For example, all crystal filters have a small amount of ripple (typ. +/- 0.5 to 1.0 dB) that can result in a slight difference in average power output between LSB and USB with some voice characteristics. But since you typically use only one of the two sidebands on a given ham band, per-band power control can conveniently compensate for small variations.
TX GAIN COMPENSATION FOR VOICE MODES (TXG VCE): If you find that your speech peaks are routinely above the desired level (i.e., higher than CW power output using TUNE), you can adjust the TXG VCE menu parameter downward in 0.5 dB steps. Conversely, if your normal speech characteristics result in lower power output compared to CW TUNE, you can increase TXG VCE above the 0.0 dB level.
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With the internal keyer running at an indicated 50 WPM, you can hear band activity between dits while using the narrowest filters.
How effective are the K3's filters for copying CW?
With the K3, you can narrow down both the 1st IF (crystal roofing filter) and the DSP (2nd IF). This makes for very nice CW copy, even if there are humongous signals outside the passband. You simply won't hear them.
We also have a CW decoder built in that will either copy and display the characters on the LCD. The decoder also works for PSK31 and RTTY, and you can transmit in these modes just by sending CW with the keyer paddle. This eliminates the computer entirely, should you be so inclined.
Can the user adjust the rise and fall time on CW? If yes, what are the steps?
The CW settings have been optimized at the factory and will not be adjustable. IF a need presents itself to make them adjustable it can be done in a future firmware revision.
Does the K3 provide a pleasant, pure sine wave sidetone for CW?
The DSP-generated sidetone could in theory be any desired waveform, but at present it's a very pure sine wave. Pitch range is 300 to 1000 Hz. The crystal and DSP filter passbands automatically center on your selected pitch. The sidetone is adjustable down to 300 Hz.
Speaking of CW .. is there a method for spotting?
There are two methods.
The first is the normal spotting tone that you tune for zero beat. TAP the SPOT switch to toggle the tone on and off.
There is also a feature called CWT. You press this button and the right half of the S Meter display becomes a zero-center tuning meter. You tune the signal in according to this bar graph. When you are close (within a hundred Hz or so either way) you can either finish tuning yourself, or TAP the SPOT button and voila -- the K3 will tune itself to zero beat. The same feature works in data modes. This is great for tuning in PSK31 and TTY signals.
There's a front-panel knob that controls the volume level of the spotting tone.
Yes. There are separate connectors for PTT in, handkey/keyer/computer, paddle, and keying out (to amps or transverters). There's also digital band data out (4 lines) and various other signals on the ACC jack. When VOX is asserted with QSK or Semi break-in transmit will occur when the key is used or when keyed from a computer. When VOX is OFF, transmission will only take place when PTT is purposely asserted, either by footswitch, or computer PTT.
Will the tuning direction change between high bands and low bands, as it does on the K2?
No.
Will clockwise tuning always make the CW pitch and the displayed frequency go up, regardless of band? That is, can you select LSB-CW consistently, regardless of band?
Yes.
Does the K3 act the same as the K2 regarding tuning direction and CW passband (LSB/USB) inconsistency between bands?
No. A common reference oscillator is used for all signal sources, and as long as it's calibrated, you'll be dead on frequency and have no pitch shift.
How does the K3 handle data modes?
In addition to the use of an external PC for data modes, the K3 includes both encode and decode for popular data modes built in!
The initial release of the K3 includes decoders for CW, TTY, and PSK31. There is a tuning indicator to assist in accurately tuning these signals. The VFO B area is a 7-character alphanumeric display that is sunlight readable, unlike the screen of most laptop PCs. Seven characters are enough to easily capture the context of the QSO.
For transmit, you can simply use your keyer paddle to send CW. The K3 automatically decodes the CW character and encodes it to the chosen data mode. You'll hear your normal sidetone at the normal level, along with reduced level audio of the outgoing data. You can also use the message memories for the supported modes.
K3 data modes are currently broken down to FSK-D (direct), AFSK-A (audio), PSK-D and Data-A. Data-A is an audio mode that can be used for various digital modes via soundcard such as PSK (audio), MFSK, SSTV, etc.
The K3 makes field operation using data modes not just possible, but fun!
Will it be possible to receive/transmit MFSK on the K3 without using an external PC?
In theory, this is just a small matter of programming. It's on the list for future consideration.
Does the K3 support FSK for RTTY?
Yes, as well as AFSK. The K3 is a great FSK radio. There are options for numbers-letters shift, inverting tones, adjustable pitch for mark and space and the frequency is based on the Mark tone instead of the suppressed carrier. In addition to computer keying the FSK via pin-1 of the ACCY connector, you can also operate true FSK without the aide of a computer using your CW paddles.
The K3 transmits AM in fully modulated double
sideband. But remember, you must have the optional 6 kHz filter installed
on the main receive board.
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Are there any options that must be installed simultaneously or can they all be added later?
Options can be added in any order. Options that must be combined are usually supplied combined. For example, the subreceiver option includes the subreceiver itself, as well as a second DSP board. These two items are only available as a single option. Each module purchased for customer installation will come with instructions. No special equipment will be needed.
How good is the K3's optional subreceiver?
The subreceiver in the K3 is full performance, not a lower-performance add-in. It uses the same circuitry as the main receiver, accommodates the same options, and has a dedicated DSP of exactly the same type. Because it is a clone of the main receiver, it covers HF+6m. It does not cover 2m, or other VHF/UHF bands.
With the subreceiver installed, will I be able to hear both VFO-A and B simultaneously thru the headsets?
Yes. We also have stereo speaker outputs and stereo PC soundcard outputs.
Is it possible to phase lock the two K3 receivers?
They run off the same reference oscillator and are phase locked.
I'm still not clear on the general-coverage (GC) receive option -- if it is indeed "optional" or available by default in a minimally configured radio.
The basic radio, as well as the subreceiver, has a full array of ham-band-only filters at the front end. This is to ensure excellent performance in the ham bands. These filters are switched in by means of relays.
The KBPF3 option is a small plug-in module that sits above the ham-band filters. It, too, has a number of filters switched in by relays. The difference is that these are wider filters, covering all of the area between the ham bands. But they share the same input/output path as the ham-band filters. When not selected, the GC filters have absolutely no effect on performance, thanks to a very careful layout that minimizes trace lengths. When you tune the radio well outside the ham bands, an appropriate GC filter is automatically selected by firmware.
Is there a panadaptor available?
The K3 does not include a built-in bandscope or panadaptor feature. We feel that in a compact, high-performance radio, optimal placement of controls should be the highest priority. A panadaptor would displace several important controls, forcing the use of "soft keys," which greatly reduce operating efficiency. However, it does include a buffered, wide-band IF output at 8.215 MHz.
Elecraft plans to offer a matching bandscope accessory after the K3 is out and the engineers get a chance to recover from the intense three-year program to develop the K3.
Will it be possible to sync the internal clock with a 10 MHz reference, WWV (or another time standard) using on-the-air pulses?
Maybe. But not at time of first shipments.
With the IF DSP in the K3, the issues that are of concern in a fully analog radio are less important. As long as the crystal filter, which is being used as a roofing filter, has reasonably good skirts and ultimate rejection, the DSP will take care of the rest. The first 30 dB or so of skirt selectivity, the passband ripple, and the ultimate rejection at the DSP IF image frequency are the most critical factors.
How many variable-bandwidth filters can be used in the K3?
Up to three of the filters can be variable-bandwidth. These filters have an additional 4-pin connector for bandwidth control. If you have the subreceiver installed, you can install three there as well. We have plans for at least two different types. The variable filters will not be available until some time after initial shipments.
Why would I use narrow roofing filters?
Let's suppose the only crystal roofing filter you have installed is 2.8 kHz wide. You put the rig into CW (or data) mode, then dial the DSP bandwidth down to 400 Hz. Everything will be fine -- unless an extremely strong signal appears "outside" the DSP's passband but still "inside" the crystal filter passband. This can cause what's called "pumping," meaning activation of the AGC or desensing. Many transceivers with IF DSP don't have the ability to do anything about this, so they get "trashed" on receive. Such transceivers typically have only a 3 kHz (or wider) roofing filter, allowing strong signals to cause trouble. The K3 has roofing filter bandwidths as low as 200 Hz, giving you a means to completely eliminating problems with nearby signals. If installed, these will be automatically selected as you narrow the DSP's bandwidth using the shift/width/hi-cut/lo-cut controls. Or you can select them manually.
As you adjust the DSP's WIDTH control (or hi-cut/lo-cut), firmware automatically selects that crystal filter which is closest to your selected DSP passband. This means you don't have to worry about manual crystal filter selection at all, normally -- let the K3 do the work. The five filter icons (FL1-FL5) will indicate which crystal filter it has selected. You can continue to narrow the DSP bandwidth all the way down to 50 Hz in every mode, and the K3 will dutifully select the best installed crystal filter. Slight differences in filter passband loss are taken into account as well.
If you have a number of roofing filters, you'll have a three-point filtering system with ultimate rejection that's basically infinite (roofing filter, DSP IF, DSP AF). Anyone who has suffered AGC pumping, desense or other problems when using wide roofing filters will notice the different the first time they use the K3 in crowded band conditions. You can select crystal filters manually if you wish using the XFIL button. When you do this, the DSP passband is set to match the selected crystal filter's passband. You can then alter it with WIDTH or HI-CUT/LO-CUT from there.
There are two other controls of interest that really simplify operation:
NORM -- This normalizes the overall system passband (crystal filter and DSP filtering) to a per-mode value, e.g. 2.7 or 2.8 kHz on SSB. This is a quick way to get back to initial conditions; it also removes any SHIFT.
I/II -- This toggles between two "presets", i.e. two previously-established combinations of DSP control settings and crystal filter selection. If you have two settings you typically use (wide/narrow for CW tuning), toggling between the two presets makes it very fast and easy. In CW mode, I usually have preset I set for 400 Hz, and II set for 100 Hz.
All of the DSP/filter settings are per-mode and per-VFO. So if you have the subreceiver installed, you can for example listen to CW at two separate bandwidths in the two receivers. The audio can be mixed, or one receiver's audio routed to the left earpiece/speaker and the other to the right. This is why we wanted two high-performance receivers with identical filter complements: versatility.
The future optional variable filters will in effect give you 4 to 8 filters in a single slot. Since crystal filters are selected automatically as you adjust the DSP controls, you can think of the variable-passband filters as DSP-tracking crystal filters -- unique to the K3.
he K3's DSP subsystem has extremely high fidelity and low IMD. Until signals reach a fairly high level, the DSP's own filtering could handle the entire job. The roofing filters, if installed, will remove very strong signals outside the communications bandwidth being used. There's also pre-DSP hardware AGC that comes in at a high level to protect the A to D converter when very strong signals are present in the crystal filter passband.
What if I want to transmit SSB via the 2.8 kHz filter but receive via the 1.8 kHz filter? Answer for main RX only and for both RXs.
You specify which filter to use for TX (one of the filters on the main RX/TX board) independently of which filters to use in RX mode. This applies whether you have a sub installed or not, and whether you're doing split or not. When you hit PTT, the TX path (on the main RX/TX board) takes over. When you release it, whatever RX-mode filters you had selected for each receiver is then in effect.
Am I right in assuming that the roofing filters listed as options are not cascaded and that you are selecting just one of the five?
Yes. Cascading increases loss and isn't really necessary since the DSP provides incredible ultimate attenuation.
If we substitute the 2.8 kHz 8 pole filter for the 2.7 kHz 5 pole filter will we get a slightly cleaner transmit signal too?
If the 2.8 kHz filter had any advantage over 2.7 kHz in a given mode, that advantage would be realized in both transmit and receive mode, if the filter were installed in the main filter bank (rather than in the subreceiver). The 2.8 kHz filter will have sharper skirts, which may be an advantage. Ultimate attenuation will be the same with either 5- or 8-pole filters because of the IF DSP.
The basic receiver comes with a 2.7 kHz filter. If the alternate 2.8 kHz 8 pole filter is ordered does that automatically mean that the stock filter will not be mounted?
Probably. I'm not sure if you would then be given the 2.7 kHz filter anyway. Check with Lisa (sales@elecraft.com).
Will Elecraft consider offering the INRAD 1.8 kHz 8-pole filter 8.215Mhz IF (711-B) for the K3, or even something narrower, for SSB contesting?
The INRAD 1.8 kHz filter for the K3 is available through Elecraft.
Will the K3 will be able to transmit through the stock 2.7 kHz (or optional 2.8 kHz) filter and switch in a narrower filter when receiving?
Yes.
Will the roofing filters be easily removable and re-locatable?
Yes. The filters are held in from below by a single screw in the middle of the filter board. You can't see the screw in the case of an 8 pole filter.
Pushing the XFIL button will allow one to toggle through the filters. Is the toggle sequence tied to the physical position of the filters mounted on the receiver board?
Yes. For this reason, we suggest putting the widest filter at FL1, etc. However, when rotating the DSP controls, the optimal crystal filter is selected strictly based on the bandwidths you've entered for each filter in the menu, so you can place them out of order if desired. You can also specify which filters are available in each mode.
Can the 12 kHz FM filter be used on AM?
Unlike most DSP-based radios, the K3 converts from the main IF (8.215 MHz) to the 15 kHz DSP IF without an intervening 455 kHz IF. This helps give the K3 a cleaner sound and better dynamic range since there are fewer conversions. However, this also means the IF crystal filter must have exceptional skirt selectivity to prevent the 15 kHz "image" from getting through. In FM mode, capture effect helps suppress the effect of "image" leakage.
AM and (E)SSB modes have far more dynamic range and the 15 kHz IF image must
be suppressed by some 10s of dB more than is required for excellent FM
operation. It is for this reason that the FM filter is recommended
only for FM use. It may also be used for AM receive, but is not
recommended for AM transmit. The 6 kHz filter has the necessary 15 kHz IF
image rejection to be suitable for use with either AM or ESSB.
With the subreceiver in the K3, can I operate split FM with only one FM filter in the main RX?
You can operate split with just one FM filter installed (on the main RX). Just turn the subreceiver off. VFO B then controls the transmit frequency in split mode, as usual. If you want to operate split with the sub RX on, a.k.a. "dual watch" in FM mode, you'll need an FM filter on the subreceiver, too.
Why does "dual watch" only apply to having the sub on? From an operational standpoint, can't I have dual watch with just the main RX? That's how the Icom 756Pro series works.
They do this by adding a second synthesizer and mixer, plus a -3 dB splitter and a following combiner, to put the two signals into a single IF I don't know of any other radios that do this, and we rejected this idea early on in favor of a higher performance, fully-independent subreceiver.
How is the KBPF3 bandpass filter used?
The KBPF3 option is a bandpass filter used to optimize the K3's SWL performance outside the ham bands. Specific bandpass filters are employed within the ham bands, once you tune outside ham frequencies, these filters are no longer active. With this option installed, users will have excellent RX performance for SWL. Also keep in mind, as stated above, any of the optional crystal IF filters can still be used at any frequency and in any mode.
Does the automatic antenna tuner work with the 10W QRP version of the K3?
Yes. Additionally, the K3 firmware does NOT support the KAT100 or the KPA100. The second antenna on the KAT3 can also be set as an RX antenna in the menu configuration.
Will the KAT3 have similar specs as the KAT100? Specifically, will it match 10:1 SWR loads?
The K3's KAT3 ATU will match a range approaching 10:1 through 100W on most bands.
Yes to both, recorded messages can also be played through the PC audio-out jack and can be saved using third-party software. The DVR will not be available until some time after initial shipping.
How long is the recording buffer in the DVR for incoming and outgoing audio?
Best answer for now is several minutes. Some buffer space will be designated to functional feedback for sight-challenged operators. How much space available for the DVR will depend on how much space this takes. Specs will be posted when testing is complete.
Can the K3's optional Digital Voice Recorder be used as a phone contest voice keyer? If so, is there a repeat feature with variable rate?
Yes to both; at least this is planned. There may be some missing DVR functionality at initial ship time, but upgrades will be fast and furious (and with a single-click). The DVR will also do general audio recording, as well as voice button feedback for blind ops.
Please refer to the antenna switching diagram for possible antenna combinations.
You can connect a dummy load to the main antenna jack (for safe TX tests at high power), but connect a real antenna to RX ANT IN, and simulate how full QSK will sound without actually putting out an on-the-air signal.
If you connect an antenna to the main antenna jack, and connect RX ANT OUT to a second receiver/transceiver, you can A/B test the two rigs just by tapping RX ANT on the front panel. With RX ANT OFF (normal), the K3 will get the antenna; with RX ANT ON, the other rig will get the antenna. (The main antenna signal appears on RX ANT OUT in RX mode if you have RX ANT ON.)
What is the isolation between the RX antenna and the primary antennas?
The latest numbers for RX ANT to ANT1/2 isolation below 10 meters are 55-60 dB typical; 10 and 6 meters is 45 dB typical.
It's our own custom-designed version of the MH2. The MH2 is identical to our old one, except much better internal mic element mounting mechanics.It is identical to the original version in both frequency response and mechanical design. We allow you to decide if you want a microphone when ordering the K3 - The MH2 is listed as an option on the order form.
Will there be any problem using the Heil HC4 or HC5 elements with the K3?
Absolutely not. We added a ton of Mic gain that can be dialed in form the front panel. ALL the Heil mics will work well. We also added 8 bands of RX and TX EQ to the K3. A user can tailor any mic's response to mimic their mic of choice (HC4/5 etc.)
I assume the K3 will continue to use Kenwood dynamic mic wiring, and I seem to remember the K3 has mic gain controlled by an encoder. Is that right?
Yes to all.
5-ppm.
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What is the accessory connector used for?
The K3 has a rich set of I/O connections. In addition to the usual key jack, paddle jack, etc., there is a 15-pin D-series connector. It includes: band data, two configurable 5V logic inputs (e.g., for FSK) and two configurable 5V logic outputs, remote power switch input, PTT, key and auxbus (e.g., for a KRC2 or transverter). While this connector looks like a VGA video connector, it is not. The K3 does not provide any sort of video output. You can get a clear idea of the rest of the K3 I/O by looking at the rear panel drawing located on the back side (where else?) of the K3 data sheet.
What is the pin-out for the DE-15 Accessory connector?
1 - DIG0 software definable TTL digital input (5V MAX!)
Used for FSK keying and possibly other uses in the future.
2 - AUXBUS
3 - BAND 1 Output (TTL)
4 - PTT input (in parallel with MIC jack PTT )
5 - COMMON (via 100 uH choke)
6 - DIG Out 0 (software definable TTL digital output)
7 - XVTR-ON (Power on signal for Elecraft XV series
transverters / TX INHIBIT
8 - POWER (pull to ground with open collector or switch to turn K3 ON)
9 - BAND 2 Output (TTL)
10 - KEYOUT-LP (Same purpose as KEY-OUT on rear panel but lower current
rating. Suitable for accessories such as sequencers.)
11 - DIG Out 1 (software definable TTL digital output)
12 - COMMON (via 100 uH choke)
13 - BAND 0 Output (TTL)
14 - BAND 3 Output (TTL)
15 - ALC input (0 to +5V MAX)
Transmit power control via the ALC input (AUX I/O
pin 15) is planned, but not finalized. We're mindful of the negative
impact ALC can have on transmit signal purity, a subject of recent debate
within testing organizations. External amplifiers vary widely in their
loop gain, causing problems with distortion. Many amplifiers, like the Alpha
87a, specifically say not to use external ALC. A properly operating,
internally ALC controlled rig like the K3 does not need external ALC
input to connect to an external amp. In general, external ALC should -not-
be used as a way to control rig power.
As for the voltage range, this is not a typo: the ALC input handles 0
to +5 V. Once ALC is working to our satisfaction, we'll provide simple
interfacing information that will allow the use of negative control voltages
(probably a resistive divider pulled up to a positive supply, or at most an
op-amp circuit).
Meanwhile, the K3's DSP-based early-stage ALC is very effective at
preventing amplifier overdrive, and should suffice in nearly all cases.
Is the K3's Inhibit input compatible with +12V? The documentation calls for a pull-up to +5V but Yaesu is using +12V in both the Quadra and the FL-7000.
No. The digital inputs to the K3 have a series 220 ohm resistor. They go directly to the PIC controller I/O pins which are rated at 5V.
What is the K3 coding for the parallel band data on the ACC connector?
The default K3 band data outputs match the Unified Microsystems plan.
160-10 m are mapped sequentially starting at 0001. 60 m is not mapped and will show up as 0000 and 6 m is above 10 m. The outputs are open-drain and thus may require pull-ups to an external supply in some applications.
What are the front panel mic wiring connections?
Does the K3 support the K2 auxbus?
Yes, the Accessory Connector provides an auxbus signal for standard, external K2 accessories. The list at present includes the KRC2 decoder and the various VHF and UHF transverters.
The KAT100 and KPA100 in an EC2 enclosure is NOT supported. The KPA100 was designed as an integral part of the K2, and specifically not as a general purpose HF amplifier. In addition, the KPA100 does not include coverage of 6 meters. The KAT100 requires considerable bi-directional traffic on the auxbus, and could lead to RFI and other issues.
What computer connections does the K3 have?
The K3 has the features of most high-end "sound card interfaces" built in. Transformer-coupled stereo line out is included. This enables you to have the main receiver and the subreceiver feed into your computer for various data modes. Transformer-coupled line input is provided, for various digital modes or other external audio sources for transmit.
The RS232 serial interface supports RTS and DTR inputs. These can be configured by use of a set up menu so either signal can be PTT, KEY or both. This meets the needs of most data mode and logging programs. We used RS232 to support users of still-popular DOS mode logging and other utility programs, as well as computers with legacy ports. Elecraft also sells a USB-to-RS232 cable that has been tested with the K3 to allow users of more modern computers complete access to the interface.
The serial port is also the means by which you can remotely control the K3. The port supports all standard data rates up to 38,400 bits per second. Firmware updates for the DSP and control processor, as well as the flash-based programmable logic, are supported via the K3 firmware update utility. It only takes a few minutes to completely reload the entire radio's firmware.
Unlike the K2, the K3 uses a standard RS-232 cable for control. We're not planning on offering extra cables at this time since these are so common.
The word is that anything that can be done from the front panel can be done from the computer interface. Is this correct?
Yes. But our remote control interface also allows the computer to send low-level signal processing and control commands directly to both the main and sub receiver DSPs, bypassing the main micro-controller. There are on the order of 100 specialized DSP commands, including those for setting up arbitrary filter bandwidths and center frequencies. I don't know if any other transceiver gives you this level of control. It'll be a lot of fun for software developers! For example, you could create your own DSP filter profiles for specialized applications.
One other tidbit: Once we've caught up with other firmware commitments, we hope to add stored macro capability, with supplemental commands for timing intervals in seconds. This would allow you to, in effect, write little applications that run on the K3 unattended, doing multi-band/-mode frequency hopping, complex beacons, hunting/scanning for "CQs" from specific prefixes in CW/data modes, etc. You'd be able to run/stop a number of individual macro sequences via the front panel.
A guy can dream, right? We'll be seeking input on all this when the time comes. Not yet :)
Can the K3 be turned on and off remotely?
The accessory jack has a contact closure input for remote on/off, and
the internal alarm clock can wake the radio up as well.
We're looking into some sort of "wake on serial port activity" but
that's not certain at this time.
Can two K3s be synchronized instead of using one K3 with the subreceiver option?
To synch two K3s together (or control two of them simultaneously in any way) will require a computer with two RS232 or USB ports, one per K3. I believe some ham control software already supports this. Over coming months we'll be adding many remote-control commands to the K3 to facilitate very sophisticated control applications.
I understand that if I short two pins from the ACC connector on the back I can turn the rig on. When shorting those two pins is it momentary or constant?
Momentary (at least 0.5 second). Or you can leave it on permanently, at least until you want to turn the rig off.
I would rather the rig could be turned on with a software command or the wake on serial suggestion made earlier.
I can't guarantee this right now, but it's on the list.
Lets talk satellite work -- can the TX freq be changed while transmitting (Doppler)?
Yes, manually. If some kind of auto tracking is desirable, it'll have to wait awhile.
Can the sub receiver be receiving at the same time as the main transmitter is transmitting?
When using the transverter ports -- maybe. Even at 0 dBm this presents a challenge, but we may be able to do it with shielding. It may also depend on the bands being used.
Can the VFOs be set to track each other?
Yes.
Will the K3 work in FM with transverters?
Yes, you'll be able to use FM with transverters.
Will the K3 display be changeable like the K2 so you get 144.xxx 50.xxx 222.xxx etc.?
The K3 will provide 9 transverter band displays. It will support all of the K2's transverter setup menu entries, but will add a number of additional control capabilities. Details are pending.
If you purchase a K3, you will definitely need to have a PC (or possibly other types of computers--we're working on that) in order to obtain firmware upgrades. The firmware is upgraded via a connection from the radio to your computer, not by installing a new IC, as with our other transceivers. This is important for two reasons:
1. The firmware will be improved over time, with new features, etc.
2. Option modules that you install "after" taking delivery of the K3 may require a firmware upgrade. For example, the subreceiver may not be ready at the time of initial shipment (it would be ready shortly thereafter). Once you install it, you may need to upgrade the firmware to use it. Upgrading the firmware is easy (typically just one mouse click). Virtually any internet connection speed will suffice for downloading the files from our web site. This is all done without operator intervention.
Is there a firmware backup utility for the K3?
A basic backup application is built into our K3 Utility program.
Yes.
At least initially. We may provide other popular control protocols later.
Yes; it has its own connector (KEY OUT) on the rear panel. The KEY OUT line is a MOSFET, open-drain (equivalent to open collector in a BJT device). The keying device is rated at 200 volts, 6 amps.
Does the K3 have a variable delay (0-20ms) to control older amp TX relays (i.e., SB-220, L4B, etc.)?
Yes. This delay is provided to prevent hot-switching of amplifiers and the adjustment range will cover any likely need.
What is the voltage and current limit to control TX amp relays?
The keying device is rated at 200 volts, 6 amps.
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What are the dimensions of the K3?
The K3 is 10W x 10D x 4H (inches). The 100W version is 8-pounds.
Is there a tilt stand included?
Yes. It's directly in-between the short and tall K2 tilt stands, at 2.0". This is exactly the right height. Trust me, we tried a few :) It's about 6.3" wide, measured between the left and right legs. This is quite a bit wider than the K2 stand. It's a custom size, using exactly the same materials as our other stands.
Our KXPD1-K2 keyer paddle adapter will work with it too, if you want a really compact keyer paddle solution for tight operating positions. It's great for picnic tables and sailboats.
The K3 definitely provides excellent audio quality on TX and RX thanks to its IF DSP, with variable bandwidths on transmit as well as an 8-band TX EQ. If you have the 6 kHz filter installed (or other widths 2.8 kHz, TBD), you can do ESSB (4 kHz) when firmware for that mode is released.
How do the transmit and receive equalizers work?
There are 8-band equalizers for both transmit and receive with a range of +/- 16 dB. When activated, a graphical display of all 8-band settings is shown on the VFO A display. The selected band for adjustment is shown on the VFO B display. And of course, you can adjust the TX settings on the fly while transmitting.
You can also set the K3 to the TX-Test mode. This allows you to make any adjustments to your transmitted signal and monitor the results....without having to transmit over the air.
What are the band ranges in terms of AF frequency?
The bands are centered at 200, 400, 600, 800, 1200, 1600, 2400, and 3200 Hz. We can easily change these if something else turns out to make sense. Also note that TX EQ will be adjustable while in TX mode.
Being a 6m operator I have a few specific questions:
Are the 6m TX and RX circuits different from the HF?
No.
What is the noise figure on 6M?
MDS is -136 dBm typical.
The K3 is optimized for high dynamic range, which requires a high-intercept preamp and mixer as well as the narrowest possible band-pass filters (consistent with good return loss). We also used PIN diode T-R switching to eliminate relays during QSK. There are small fro
