Elecraft K2VCOSHLDKT User Manual download pdf

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Elecraft K2 VC O Sh ielding Inst ructions

Rev. E, Oct. 6, 2005

The K2’s VCO (voltage-controlled oscillator) may be susceptible to low-frequency modulation by nearby large power transformers,

such as those found in high-current linear power supplies and antenna rotator controllers. Since the magnetic field from a

transformer falls off rapidly with distance, such modulation can usually be eliminated by simply moving the equipment away from

the transceiver (or moving it to the right side of the transceiver, farther from the VCO circuitry). In difficult cases, magnetic

shielding can be used, alone or in combination with repositioning of equipment.

These instructions describe how magnetic shielding can be added to the K2. Toroidal transformer T5 must be replaced with a

smaller iron-powder core that can be shielded by a high-permeability ferrite sleeve. In addition, slug-tuned inductor L30 must be

electrically disabled since it, too, is affected by magnetic fields. With L30 out of the circuit, the VCO inductance can still be

adjusted, if necessary, by squeezing or spreading the turns of T5. A DMM (digital multimeter) is used during this adjustment.

Parts Inventory (Order #K2VCOSHLDKT)

(1) E680013 T37-6 toroid core (yellow)

(1) E680024 Ferrite toroidal sleeve (dark gray), 16 mm OD, 12 mm ID, 8 mm tall (0.63 x 0.50 x 0.32”)

(1) E500003 470 ohm, 1/4-watt resistor

(2) E700021 4-40 nylon hex nut

(1) E700107 4-40 x 5/8” (16 mm) nylon machine screw

(1) E700108 Nylon flat washer, 5/8" (16 mm) diameter

(1) E700109 Paper flat washer, 5/8" (16 mm) diameter

(2 ft.) E760002 #26 red enamel wire

(1 ft.) E760004 #26 green enamel wire

Modification Instructions

 Turn off the K2 (or K2/100) and disconnect all external equipment.

 Remove the top cover, disconnecting all cables.

 Remove the bottom cover (flat part only — not the heatsink/rear panel).

 Locate slug-tuned inductor L30, which is near the left side panel and adjacent to toroidal transformer T5. In the next step, L30

will be isolated from the VCO, so it can no longer be used to adjust the VCO frequency. The new method is explained later.

 Find L30’s pads on the bottom side of the RF board. Cut the trace identified in Figure 1 that connects L30 to pin 2 of T5. Use

the tip of an Xacto knife or other sharp tool. Inspect the trace using a magnifying glass to ensure that it is cut.

Figure 1

 Locate R10 (top side of the RF board, near L30). Remove R10, being careful not to damage the pads. Re-install R10 on the

bottom side of the RF board, using the same pads. (If R10 is damaged, use the 470-ohm resistor supplied with this kit.)

 Locate T5 (near L30). Remove the nylon hardware holding T5 to the RF board.

 Unsolder all four leads of T5 and remove it, being very careful not to damage the pads or traces. One method is to hold a lead

with long-nose pliers, heat the joint completely, then pull the lead out slowly.

 Clean T5’s four holes out completely using solder wick or a vacuum desoldering tool.

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Summary of Contents

Page 1 - Figure 1

Page 1Elecraft K2 VC O Sh ielding Inst ructionsRev. E, Oct. 6, 2005The K2’s VCO (voltage-controlled oscillator) may be susceptible to low-frequency

Page 2 - Figure 2

Page 2 Locate the T37-6 core (yellow), which is smaller than the original T50-6 core. It will be used to wind a new T5. As shown inFigure 2, T5 wil

Page 3 - Figure 5

Page 3 Look closely at T5’s leads where they exit the holes on the bottom side. The leads must have no enamel residue, and should betinned so that

Page 4 - Figure 6

Page 4 Place the ferrite sleeve over T5, aligning both the ferrite sleeve and paper washer with T5’s component outline. Place the 5/8” (16 mm) di

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Elecraft K2VCOSHLDKT User Manual

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