Better Music Builder DX-211 Specifikace stáhnout pdf (Strana 5)

From March 2000 QST © ARRL

quite informative. Someone mentioned that

they really missed not having a dimple on

the main tuning knob. Someone else noticed

that the knob on their Yaesu FT-100 was

about the same size. Subsequent postings

indicated that the parts sales staff at Yaesu

quickly learned that all these knobs were

being ordered for Elecraft K2 radios—not

Yaesu FT-100s. Within two days they had

sold out their entire stock of replacements!

In another posting, a European builder

circulated a question regarding degraded

receiver performance after installing the

noise blanker option. After several

questions about measurements and hearing

from a few others who had noticed a similar

effect, Wayne and Eric went to work

tracking down the problem. Their response?

A change in the design of the noise blanker

and an upgrade kit for the earlier version.

The optional noise blanker that we

received with our initial K2 shipment

several months ago was the “original”

version. With it installed, our lab tests

revealed reduced intermodulation distortion

dynamic range and blocking dynamic range

and a degraded third-order intercept

point—even with the noise blanker

deactivated. Elecraft provided us with the

upgrade. Table 1 reflects the performance

that we measured with the latest version of

the noise blanker installed.

If you have Internet access, once you’ve

ordered your kit, I highly recommend that

you subscribe to the reflector. Send an e-

mail to [email protected] with

subscribe elecraft in the body of the

message. You can also view the list archives

at http://www.elecraft.com.

Back to Building

After completing the first-stage

alignment and testing, the boards are

removed from the partially completed

enclosure and the remainder of the

components are installed on the RF board.

Most of your efforts will be in assembling

the receiver section. Here you will wind

your first toroidal inductors and

transformers. The K2 contains a total of 14

toroidal inductors and six toroidal

transformers. In addition, there is one

transformer wound on a binocular core.

Because time was running short to

complete this review for this special QRP

issue, once I’d finished up the receiver

section, I turned the kit over to Zack Lau,

W1VT, for completion of the transmitter

section and the final alignment. Zack

reported no major difficulties, except that

I had installed RFC3 in L16’s spot and vice

versa. This caused some problems with the

receiver on 40 and 80 meters. Once Zack

located and corrected my error, everything

was fine. In my defense, the label for RFC3

is directly between the locations for these

two inductors. Don’t let this happen to you!

Be careful to identify the correct location

for every part before you install it, and

recheck before soldering.

Alignment and Testing

The alignment steps involve adjusting a

few tuned inductors and variable capacitors

to set the voltage controlled oscillator and

the various tuned circuits. The control

software performs a procedure to linearize

the VFO operation across the tuning range.

You also adjust the crystal filter settings and

the BFO settings for each mode and band.

The filter scheme is especially interest-

ing. Most commercial transceivers come

with a “stock” filter for sideband and a

narrower filter for CW operation. In

addition to these there is usually room to

add one or two additional optional filters.

The K2 uses a scheme of diode switching

and software control to provide four crystal

filter settings for each mode. These are ad-

justable, so you can tailor the bandwidths

to suit your operating style. The factory

default settings for CW are 1.5 kHz and

700, 400 and 100 Hz.

You also set up four filter bandwidths

for SSB reception. The defaults are 2.2, 2.0,

1.8 and 1.6 kHz. (You can still receive SSB,

RTTY and the data modes even with a basic

“CW Only” K2).

If you should decide to add the SSB

adapter, there is yet another filter—

optimized for SSB operation at about

2.3 kHz. In that case, filter 1 is optimized

for SSB transmit and filter 2 is optimized

for SSB receive. Filter 3 can be set as a

narrow bandwidth SSB filter. The default

is 1.6 kHz. Filter 4 can even be set at a

narrower bandwidth—useful for the data

modes.

Some builders have reported confusion

about the procedures for aligning the filters

and BFO settings. When we followed the

steps in the Owner’s Manual we came close,

but the settings were not “perfect.” There

have been several discussions about this on

the e-mail reflector, including postings

about programs to download that will allow

you to use your computer’s sound card as

an audio spectrum analyzer. Elecraft has

indicated that they will be changing some

of the procedures in the manual.

The K2’s control software includes

extensive diagnostics. If you turn on the

radio and the display shows “LOW BATT,”

the software is telling you that the battery

or power supply voltage is too low, a

display of “HI-CUR” on transmit indicates

that the user-programmable current level

was exceeded, and so on. Troubleshooting

charts are provided. This could be es-

pecially helpful if you run into difficulties

getting the radio working initially.

Figure 5—A closer look at the completed control board. The glass epoxy boards

have plated through holes and the component identifications and locations are

clearly silk-screened on the boards.

How Did It Do in the Lab?

The technical performance of radios comes out during lab testing. Usually, the transmit IMD

and receiver dynamic range results separate the toys from the big boys. Usually!

On SSB, this radio is clean. As seen in Figure 1, the high-order intermodulation products

are quite good. The CW keying is nice, too, as shown in Figure 3. No key clicks from this baby!

But where the K2 really shines is in its receiver performance. On average, transceivers

positioned in the upper tiers of the popular HF product lines (in the $2

000

to $35

price class)

exhibit blocking dynamic range measurements somewhere in the vicinity of 13

dB and a two-

tone, third-order dynamic range near 95 dB. The K2’s receiver performance compares very

favorably to that of the samples of the high-end radios we’ve recently examined, turning in

impressive 136/97 dB figures for these parameters.

The fact that a radio in this price class—and a home-built one at that—can stand proudly

in such company is a remarkable accomplishment. This is the first-generation radio that Elecraft

has produced. I can’t wait to see the next one!—

Ed Hare, W1RFI/QRP, ARRL Laboratory

Supervisor

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