Elecraft K4 – New Product

Q:  What are the K4’s basic capabilities?

A:  The K4 is our new top-of-the-line transceiver, a direct-sampling SDR with a user interface that incorporates a large color LCD. It covers all ham bands from 160-6 meters, with planned coverage of 2 m and 70 cm as a future option. Main and sub receivers each cover 100 kHz to 54 MHz. It operates in all modes (SSB, CW, AM, FM, and DATA), and includes built-in text decode/encode (CW, PSK31/63, RTTY). Power output is nominally 100 W (10 W for the QRP version). The KAT4 antenna tuner has 3 jacks, and there up to 5 receive antenna sources. I/O is extensive, including HDMI video output, Ethernet, 4 USB ports, and a superset of K3S analog and control connections. 

Q:  All that and it’s still easily transportable?

A:  Yes. Elecraft is committed to providing dual-use transceivers, even at the high end, in support of Field Day, DXpeditions, RV travel, etc. At 4.5 x 13.5 x 11.0” (less projections) the K4 is larger than a K3S, but it still weighs only about 10 pounds. It’s also very power-efficient for a radio in its class (2 A typical on RX), and can run from as low as 11 V, e.g. from a vehicle battery.

Q:  Are there other products in the “new” K-Line?

A:  Yes. There’s the K4’s companion amplifier, the KPA1500, as well as the new SP4 speaker, one or two of which can be directly connected to the K4. Both the amp and speaker are the same height as the K4 and have the same styling. The K4 is also compatible with our K-Pod station controller and MH4 microphone, as well as other K-Line gear such as the KPA500 amp and KAT500 ATU.

Q:  How do K4 owners benefit from its modularity?

A:  In two ways. First, you can tailor the K4 to your own requirements at initial purchase, adding advanced options or upgrading to a K4D or K4HD at any time. (The three models and other options are discussed below.) Second, modularity allows Elecraft to quickly take advantage of new technology in the future by upgrading only the affected modules.

Q:  Are there different models of the K4?

A:  Yes: The K4, K4D, and K4HD. In most ways the three are identical. The K4D adds a second A-to-D converter and a second set of bandpass filters, allowing the radio to work in diversity mode or other situations where it’s beneficial to use separate antennas for the two receivers. (Thanks to direct sampling, neither the K4 nor K4D require crystal filters.) The K4HD adds a dual superhet module (discussed below), improving blocking dynamic range for high-signal conditions. Each of its two superhet sections has two crystal filters, one for SSB/DATA bandwidths and one for CW. Since each section has a high-dynamic-range I.F., no additional crystals are necessary. Note that a K4 can be easily upgraded by the user to a K4D, or a K4D upgraded to a K4HD, at any time. No soldering or alignment is required.

Q:  How does the K4 compare, overall, to a K3S and P3?

A:  The K4 retains virtually all of the operational features of the K3S and P3, while adding direct-sampling technology, wide-range dual receive as a standard feature, advanced I/O, and a large (7”) display with touch capability. With its high level of system integration, the K4 takes up about 4” less desk space (horizontally) than a K3S + P3. Despite this, the K4 is still easy to operate, thanks to optimal use of its display and context-sensitive controls. Most of the “hard” controls are similar or identical to those of the K3S, making them immediately familiar to anyone who has used a K3 or K3S. And unlike most transceivers in its class, the K4 has separate optical encoders for VFO A,VFO B, and RIT/XIT offset.

Q:  Can a K4 be remote-controlled?

A:  Yes. You can control a K4 from another K4, or from tablet/notebook/tablet computers, directly via the Ethernet. No USB to Ethernet adapter is required. Panadapter signals are displayed on all remote-control devices.

Q:  How does the K4’s CW performance compare to that of other direct-sampling SDRs?

A:  Elecraft may be unique in the number of CW ops we have among our engineering staff. Nothing gets out of the Elecraft lab until it has silent T/R switching (PIN diodes, not relays) and fast, clean QSK. Some SDRs and direct-sampling radios have serious compromises in CW mode due to the use of T/R switching relays and long signal processing delays that make QSK impossible. The K4 uses fast parallel processing of digital signals to ensure low latency during T/R switching. In addition there are many features for CW operation, including our high-resolution mini-pan tuning aid, dedicated one-touch message play switches, text decode/encode, top-level controls for setting pitch and code speed, adjustable keying weight, and an audio peaking filter (APF) that works like magic on weak signals buried in noise.

Q:  Are there provisions for running software applications inside the K4?

A:  Yes. The K4 incorporates a powerful, fast-booting, Linux-based computing module. This module manages the LCD and streaming I/O, including HDMI, Ethernet, etc. But it is also a general-purpose computer that can accommodate future in-box applications such as logging, external equipment control, even advanced data modes. Elecraft will seek input from the user community regarding such applications, then tailor them to the K4.

Q:  Does this mean that the K4’s software is “open-source”?

A:  No. But we’ll be providing an API (application programming interface) to allow selected developers access to internal resources. Any applications or other software contributed by third parties will be thoroughly vetted by our team prior to becoming available.

Q:  How do superhet transceivers, like the K3S, differ architecturally from a direct-sampling radio like the K4?

A:  A superhet depends on crystal filters to provide selectivity in both transmit and receive modes. The K4 uses true direct-sampling at the RF input and achieves its selectivity through digital signal processing. In this scheme, a high-speed analog-to-digital (A-to-D) converter digitizes signals coming in from the antenna jack (we digitize at a rate of about 122 MHz). Signals in this form can be filtered, displayed and demodulated using DSP techniques. This allows radio designers to add new operating modes, etc., without updating the hardware.

Q: Are there performance differences?

A: In most circumstances, superhet and direct-sampling transceivers can both provide excellent performance and versatility. That said, here are the two most important differences: (1) In a direct-sampling radio like the K4, the DSP can “see” a wider bandwidth in its signal chain, allowing it to provide higher-performance noise reduction, noise blanking, advanced filtering, automatic signal tuning, and other advanced signal processing features. In contrast, a superhet’s DSP sees only the narrow bandwidth available at the output of its crystal filters, limiting it to audio-bandwidth signal processing. (2) The K3S, a superhet, has among the highest receive blocking dynamic range figures of any radio. The K4 can be outfitted with a dual superhet module that provides essential the same performance if required. (See K4HD model, described below.) This level of dynamic range is required only for stations that experience extreme signal levels, such as might be encountered in a high-power multi-transmitter installation without supplemental RF filtering, or if you’re next-door to an AM or SW broadcast station. Direct-sampling-only radios like the K4 and K4D can easily handle signals encountered by most operators during typical home or field use.

Q:  I’ve heard the term “slice receiver” used in conjunction with direct sampling SDRs. Does the K4 use these?

A:  Yes, but in the K4 this technology is strictly “under the hood,” implemented in a way that is transparent to the operator. Instead, you can just think in terms of the main receiver (VFO A), sub receiver (VFO B), and panadapter, as you would for a K3S and P3. But since you asked: A “slice receiver” is a digitized receive signal stream. With direct sampling, a single A-to-D converter can in theory provide any number of such digitized streams, simultaneously. The trick is using them wisely! In the basic K4, which has one high-performance 16-bit A-to-D, we extract three such streams. One is wide bandwidth, used for the panadapter. The other two are for the main and sub receiver streams, which are demodulated by a high-speed DSP. These are the streams you listen to. In the K4D or K4HD there are two A-to-Ds, providing more independence for the receive signal streams. We can use the second ADC’s panadapter stream to improve performance for dual-pan mode, and use one of the second ADC’s demodulation streams to allow diversity operation, which requires two separate antennas. You can think of these as “slices” if you like (as will be explained in the theory of operation). But you won’t see this term on the radio itself or in the operating instructions.

Q:  What are the K4’s DSP features?

A:  DSP features include easy-to-adjust, per-mode RX/TX EQ; clean, punchy RF speech processing; full DVR capabilities; and several built-in data decode/encode modes. Direct-sampling technology results in an ultra-flat passband response for clean RX and TX audio. Since the signal chain is software-defined, the DSP can be field upgraded to add new algorithms and operating modes.

Q:  What are the features of the KAT4 ATU?

A:  The KAT4 ATU has a nominal 10:1 matching range. It includes 3 antenna jacks, any one of which can be selected as a receive input at a given time (bypassing the ATU’s L network). This selected antenna can then be used by either or both receivers, in addition to the other receive antenna sources (RX ANT 1 and RX ANT 2). The KAT4 stores up to 32 LC settings per ham band, recalling them instantly based on VFO frequency (recalled on transmit). In most home stations, ATU setup can be done one time for all bands/antennas.

Q:  Is it possible to use two independent receive antennas while using a third antenna for transmit?

A:  This is possible with the K4D or K4HD. (A basic K4 can be upgraded to a K4D at any time by adding the KDIV4 option.) For example, the main receiver could use RX ANT 1, while the sub receiver uses RX ANT 2, or either could use one of the KAT4’s 3 antennas. The transmitter can also use any of KAT4’s antennas. Transmit, main RX, and sub RX antenna selections are all clearly indicated on the display at all times

Q:  What are features of the planned internal VHF/UHF module?

A:  This internal module is intended to cover the 2 m and 70 cm bands, though other bands may be a possibility. The target power level is about 15 W. The module will function in all operating modes. Controls for FM and repeater setup are included in the K4’s software. The ANT 4 jack on the rear panel is reserved for use with this module. If separate VHF and UHF antenna jacks are preferred, one of the 3 KAT4 antenna jacks could be repurposed for this.

Q:  Will there be a kit version of the K4?

A:  A kit version is planned for later release, though no specific date has been set. This will be a no-soldering kit, like the K3S and P3. Builders will learn about advanced radio technology as they proceed. All modules will be pre-aligned and tested.