Connections And Controls - K1EL K45 Manual

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User manual (37 pages)

Table of Contents

Figure 10 — The upper board contains the display and controls.

When this photo was taken, the 16-pin connectors to join the two

PC boards had not been installed, and the protective film was still

in place on the OLED display. The microcontroller will be plugged

into the empty socket in one of the final steps.

flush with the board, some are bent over, and others

require closely trimmed leads.

The lower board carries most of the receiver and trans-

mitter RF circuitry (see Figure 11). The IRF510 final

amplifier is mounted with a small heatsink, mica insu-

lator, and plastic washer. Mounting the final amplifier and

heatsink requires some care. The IRF510 leads have to

be bent correctly before soldering so that the insulating

material lines up. There are seven toroid inductors and a

bifilar wound transformer, and these are all supplied pre-

wound with tinned leads. They install just like any other

part. A crystal filter following the mixer uses four matched

crystals in series. The crystals are labeled 1 – 4 and are

installed in the corresponding spot on the PC board.

One of the things I really like about this kit is that all of

the connections between the upper and lower boards

are made using two 16-pin connectors. All of the

switches and controls mount to the boards, so there are

no interconnecting wires at all. The upper and lower

boards simply plug together using the two connectors

and are secured with machine screws and spacers.

Adjustments and Final Assembly

At this point, the radio is fully assembled but not placed

in the case until you perform some checks and adjust-

ments. Before applying power to the boards, the instruc-

tions show a few simple ohmmeter checks for power bus

shorts. Then connect an antenna and speaker or head-

phones, apply power, and listen for signals on the four

bands while checking operation of the display and

controls. At this point, the receiver sounded deaf, so I

stopped there to recheck my work. Because of the way

the board interconnections are done with the two 16-pin

connectors, it was easy to pop the boards apart and

inspect everything with a magnifier, revealing a bad

solder joint on the filter switch. With that fixed, the

December 2022

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Figure 11 — The lower board has the RF and audio components.

The final amplifier FET is on its heatsink in the center of the board.

All of the toroids are pre-wound with tinned leads. The instructions

clearly indicate the core color and number of turns, so you can

double-check that you have the right part. The numbered and

matched crystals for the narrow CW filter are along the bottom edge.

receiver sounded fine on all bands, so I moved on to the

final adjustments with the radio connected to a watt-

meter and dummy load.

Several trimmer potentiometers need to be adjusted. The

first trimmer is set to just barely light the blue

with no signal present. It glows brightly with strong

received signals. The next step requires a multimeter in

series with the power supply that can measure current of

around 100 mA with a resolution of a few milliamps (most

digital multimeters will work here). In this multistep pro-

cess, watch the current draw while adjusting the

trimmer to set the operating point for the final amplifier

FET. This should be a set-and-forget adjustment. Next,

adjust the sidetone level trimmer for comfortable lis-

tening.

Now adjust the low-voltage alarm trimmer to light the red

LED when the power supply voltage drops

LOW BATT

too low, helping to keep your battery from excessive dis-

charge. The alarm range is about 9 – 11 V. I set mine

with an adjustable power supply. This isn't a critical

adjustment — it's just an alarm to warn you that your

battery is getting low, and it doesn't affect operation of

the radio.

The final trimmer centers the audio band-pass filter fre-

quency at 700 Hz. The instructions suggest using an

oscilloscope or audio meter to adjust for maximum

signal, but it's easy enough to do it by ear.

With the trimmers adjusted, it's time to put the radio in

the case and get on the air.