Better Music Builder DX-211 Specifikace stáhnout pdf (Strana 6)

From March 2000 QST © ARRL

A Few Circuit Details

The K2 uses a modular design that

allows flexibility and opportunities for

future expansion. The display board

provides the user interface, including the

display and all the controls. The control

board contains the main microprocessor, the

dc control signal circuits, the AGC circuit

and the audio amplifier. The RF board

serves as a “motherboard” for these two

boards and any optional boards. In addition

to all the RF circuitry, this board contains

the I/O controller and the latching relays

that select the operating band.

The receiver is a single-conversion

superheterodyne that employs double-tuned

band-pass filters for each band. It uses a

down-conversion scheme with an IF of

4.915 MHz. The individual band-pass

filters provide superior IMD performance

when compared to up-converting designs

that often use a single low-pass filter to

remove image products. Because the BFO

is microprocessor controlled, its frequency

is reset for USB and LSB reception as well

as CW on either side of the carrier.

In transmit, the signal flow reverses,

with the output signal going through the

band-pass and low-pass filters. The RF

amplifier can produce over 10 W and is

designed to provide good immunity to high

SWR. PIN-diode T-R switching results in

silent QSK operation.

The microprocessor firmware controls

just about every aspect of the K2’s

operation. There are many routines that run

behind the scenes. For example, the PLL

reference oscillator is linearized on each

band by an auto-calibration routine. The

results of this routine are stored in

EEPROM tables for use each time you turn

on the radio. The firmware also supports

features like built-in test equipment, a

memory keyer, dual VFOs with split

operation and frequency and band stacking

memories. Provisions are included for a

variety of optional modules, such as the

SSB adapter, the noise blanker, the

automatic antenna tuner and so on. With

just 8 kilobytes of memory in the PIC

16C77 microcontroller, it’s readily apparent

that the control program code has been

highly optimized!

The I/O controller is a coprocessor IC.

The SSB adapter board carries its own co-

processor, as do some of the other optional

modules. This has several effects. It

simplifies the primary control circuitry and

allows the accessory coprocessors to “go

to sleep” when they aren’t needed, saving

valuable current for battery operation. It

also reduces the amount of digital noise on

the RF board that might cause receiver

interference.

Speaking of saving battery current,

several other power saving features are

worth mention. The S meter/RF output

meter LED bargraph can be set to bar, dot

or off. The LCD display backlighting can

be turned off. With the LCD set for

nighttime operation, the LED bargraph

brightness is reduced slightly and when the

LCD is set for daytime operation the LED

bargraph is brighter to make it easier to see.

Latching relays are used for all filter, VCO

and option switching, so there is no relay

current drain during normal operation. By

careful power management, the total

receive current requirement can be as low

as about 150 mA. This is an order of

magnitude lower than typical HF

transceivers.

The K2 uses a PLL synthesizer IC and a

wide-range, band-switched voltage

controlled oscillator. A 12-bit DAC gives

the fine-tuning steps on the VCO, which is

the PLL reference oscillator. Three DPDT

latching relays select one of eight VCO

ranges for the synthesizer.

A 5-pole variable bandwidth crystal

filter is used in front of the IF stage. (With

the SSB adapter, a separate fixed filter is

switched in.) This filter is optimized for

narrow bandwidths of about 200 to 500 Hz,

but it can be adjusted wider or narrower if

desired. A second two-pole crystal filter

follows the IF amplifier. This filter can also

be tuned, but over a smaller bandwidth

range. The AGC signal is derived from the

IF amp output using an auxiliary low

frequency IF of about 150 kHz.

The Finished Product

The completed K2 is an HF transceiver

with many of the features that we have

come to expect on the ready-built

commercial rigs. The small-sized front

panel has a nice ergonomic design that

allows my big clumsy fingers to find the

right controls without knocking all the other

settings out of whack. The well-thought-out

layout results in very intuitive operation.

The main tuning knob, in the center of

the front panel, enjoys plenty of space

around its perimeter. Four control knobs to

the left side of the front panel adjust the

keyer speed, the output power, the audio

gain and the RF gain. One knob to the right

of the main tuning knob controls transmit

and receive incremental tuning.

The rest of the control operations are

handled by push-buttons. Each button

serves two purposes—one when you tap it

briefly and another when you hold it in for

a second. Labels above and below each

button indicate these functions.

With these buttons you can step up or

down through the bands, directly punch in

frequencies, store and recall memories (ten

memories are available), select the mode,

choose VOX or PTT operation, switch

between VFO A and B, equalize the VFO

settings, select split frequency operation,

reverse the transmit/receive frequencies

momentarily and automatically scan for

CW signals over a programmable frequency

range. You can also activate the pream-

plifier and RF attenuator, select the fast or

slow AGC (and even turn the AGC off!),

cycle through the filter options and enable

RIT and/or XIT. The SPOT key turns on the

sidetone oscillator during receive so that

you can match the received tone of a CW

signal to your sidetone oscillator to ensure

that you are tuned to zero beat. CW RV lets

you listen on the opposite side of a signal.

The

MSG

REC

button provides access to

the 9 message memories in the built-in

electronic keyer. Hold this button to begin

the memory record, then tap a number button

and send the message you would like to store.

When you pause for more than a few seconds

(or if you tap the

MSG

REC

button again)

recording stops. You play the memory

contents by tapping

MSG

REC

and then the

appropriate number button. Messages can

also be repeated at a programmable internal.

Figure 6—An internal view with the top cover removed. The display and control

board plug into the RF board along its front edge. Note the almost total absence

of point-to-point wiring. The rear apron is pre-punched for a wide variety of

available and proposed optional accessories.

1 2 3 4 5 6 7 8 9

Komentáře k této Příručce

Žádné komentáře

Better Music Builder DX-211 Specifikace Strana 6

Komentáře k této Příručce

Související produkty a manuály pro Audio zesilovače Better Music Builder DX-211