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Monday, May 6, 2013

9M2PJU Playing With Elecraft K3 Transceiver




Elecraft’s state-of-the-art K3 transceiver offers a unique combination of ultra-high performance and affordability.

Both 100-watt and 10-watt (upgradeable) models are available. No-soldering kit; also available fully assembled and tested, the K3 is comparable in both features and performance to transceivers listing at up to six times its price.

In a first for the industry, the K3’s identical main receiver and subreceiver each feature a high-dynamic-range, down-conversion analog architecture. This allows Elecraft to provide roofing filters with bandwidths as narrow as 200 Hz, while up-conversion designs have roofing filters typically 3,000 to 15,000 Hz in width. Unlike some competing down-conversion designs, the K3 also provides 6-meter coverage, as well as continuous tuning from 0.5 to 30 MHz. Each receiver has its own bus-switching mixer, narrow ham-band front-end filters, 32-bit I.F. DSP, low-noise synthesizer, and up to five crystal roofing filters.

The K3 is the only deluxe transceiver that is targeted at both home and field use. Weighing just 8 pounds and having dimensions of 4” x 10” x 10” HWD (10 x 25 x 25 cm), it’s well-suited to demanding DXpedition or Field Day operations. Its receive-mode current drain of less than 1 amp greatly facilitates battery or solar-powered mobile/RV/marine installations. But unlike smaller portable transceivers, the K3’s user interface is optimized for ease of use, and its feature set rivals units many times its size and weight.

The transceiver is offered both factory-assembled and as a modular, no-soldering kit. Either way, K3 owners can start with a basic version of the transceiver, at lower cost, then easily add modules later, such as the internal subreceiver, ATU, and 100-W stage. To ensure identical performance of both pre-built units and modular kits, modules are 100% assembled and tested at the factory. Builders learn the radio theory behind each of the modules during assembly, and acquire skills that will enable them to easily add future modules or upgrades.

Two 32-bit digital signal processors provide true software-defined features, along with expansion memory to handle future signal processing tasks and operating modes. The operator will have full control over any operating situation, with 8-band receive and transmit EQ, stereo speaker/soundcard outputs, binaural effects, and advanced noise reduction. Also included is built-in PSK31, CW, and TTY decode/encode, so the operator can enjoy the excitement of data communications with or without a computer. The rig’s rich I/O complement includes an isolated sound card interface, front/rear mic/phone jacks, dedicated serial I/O, and band data. An optional module provides transverter in/out and RX antenna in/out jacks. The latter allow the use of RX-only, in-line filters for extreme operating environments.

Available options include: built-in 100-W automatic antenna tuner with two antenna jacks (KAT3), subreceiver (KRX3), general-coverage front end band-pass filter module (KBPF3), 100-W stage (KPA3), RF I/O unit for RX antenna, IF Out and transverter interfacing (KXV3A), digital voice recorder (KDVR3) and our all mode 2-m (144-148 MHz) all mode internal option (K144XV).

What "Roofing Filter" means to Elecraft

K3 Filters and Dynamic Range

There's been so much discussion about this topic that I'd thought I'd better try to clarify why we used the term when announcing the K3.
A "Roofing filter" is simply a filter in the radio's first IF through which all signals must pass before they will be "seen" by later receiver stages. The narrower this filter is, the less exposure later stages will have. Thus a "narrow" roofing filter is desirable -- but "narrow" is relative, as I'll explain.

The term "roofing filter" has most often been used in relation to triple- or quadruple-conversion receivers. Such receivers have an  IF above the highest RF band covered; it's typically something in the range of 30 to 70 MHz or higher. But "roofing" as a term should be interpreted as "protective," not "high in frequency." A roofing filter protects later stages, including amplifiers, mixers, narrower filters, and DSP subsystems, just as the roof on your house keeps rain out of all of the rooms. But a roofing filter can be equally at home at a low first IF, if that is how the radio is designed. It still provides the same protective function.

When we released the K2 in 1999, we never described our 1st IF crystal filters as roofing filters. We had only one IF, so the receiver model was simpler; there were no narrow filters at later stages that required protection.

But in 2007, we find that the term is in widespread use. Average hams now think of roofing filter bandwidths as the standard of comparison between receivers. This is why manufacturers have jumped through hoops to try to provide the narrowest possible roofing filters. Many operators have an understanding (justified) that a roofing filter that is wider than the communications bandwidth will not best protect the receiver's later stages. So the term now seems appropriate to use even in a radio such as the K2, K3, or Orion, all of which use low-frequency IFs (5 to 9 MHz).

In recent years, the roofing filter has become the centerpiece of receiver redesign:
Suppose that manufacturer "A" initially designed their receiver to use a 15- or 20-kHz roofing filter. Yes, this allows the receiver to handle NBFM and other wide modulation modes; it may also be selected to constrain the signal bandwidth ahead of a noise blanker or spectrum scope. But it comes at a price. If you're using CW mode, you'll have much narrower filters selected at the radio's 2nd and 3rd IFs. Yet the 1st IF roofing filter allows a broad swath of signals into the earlier stages. You don't need this energy in your passband. It can cause trouble.

Manufacturer "A," realizing they have a problem with dynamic range at close spacing, then announces that they've had a breakthrough: they can now offer a 6-kHz, or more recently 3-kHz roofing filter. This will certainly improve the situation for SSB and AM operation, but it still opens the barn door in CW or DATA modes, because the bandwidth is a factor of 10 wider than needed for communications.

So why don't they offer much narrower roofing filters that can be switched in for CW and data modes, or at times when adjacent-channel SSB QRM is very high? It's because they can't make filters any narrower at such a high IF.

Enter the "down-conversion" rig (K2, K3, Orion, etc.). By converting to a low first IF, the designer can easily create narrow filters that are compatible with the required communications bandwidth. This is why we are offering filters with bandwidths as low as 200 Hz.

And yes, these are still "roofing" filters, because they limit exposure (bandwidth), thus protecting later stages (in the K3 case, the IF amp, 2nd mixer, and DSP).

http://www.elecraft.com/K3/Roofing_Filters.htm


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 net overall IF gain.
Once a filter is installed, you can specify which modes it is available in (or all modes).

http://www.elecraft.com/K3/K3FAQ.htm#roofing filter loss

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.

http://www.elecraft.com/K3/K3FAQ.htm#noise blanker

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.

http://www.elecraft.com/K3/K3FAQ.htm#NR

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.

http://www.elecraft.com/K3/K3FAQ.htm#pbt

For more info please visit http://www.elecraft.com/K3/K3.htm






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