Elecraft CP1 User Manual download pdf

ELECRAFT CP1 DUAL DIRECTIONAL COUPLER

R e v B , J u n e 7 , 2 0 0 6

The Elecraft CP1 is a dual directional coupler that provides high directivity, can be internally or externally

terminated and can be constructed with a coupling loss of either 20 dB or 30 dB. It can be used to sample a

transmitter’s forward and reflected power output. For example, it can be used as tap point for IMD

measurements in conjunction with the Elecraft 2T-gen (2-tone generator).

Specifications

Frequency Range 1 MHz to 30 MHz

Coupling Loss 20 dB or 30 dB (29.8) +/- 0.25 dB

Directivity 30 dB typical

Power Rating 30 dB coupler, 250 watts; 20 dB coupler, 25 watts

Parts List

(1) CP1 Printed Circuit Board E100191

R1, R2 (2) Resistor, 51-ohm, 3W Resistor E500178

S1, S2 (2) Miniature slide switch E640009

J1-J4 (4) BNC Connector E620020

See text (2) Toroid Cores, FT50-43 E680008

(2) Toroid Cores, FT50A-61 E680025

(4) Self-adhesive mounting feet E700024

(10 ft.) #26 red magnet wire E760002

(3 in.) #18 gray insulated wire E760021

Assembly

 Before winding the toroid inductors, decide whether you want to construct the CP1 as a 20 dB

coupler or a 30 dB coupler. For power levels of 25 watts or less, a 20 dB coupler will result in greater

useful measurement range with commonly-used detectors. With power levels higher than 25 watts, a

30 dB coupler will be more useful.

 Use a permanent marker to write the coupling loss in the space provided on the printed circuit board.

See the photographs on page 3.

 If you are constructing a 20 dB coupler, 10 turns will be wound on each toroid core. If the coupling is

to be 30 dB, then 31 turns will be used. For 10-turn windings, cut two 12 inch (36 cm) lengths of

magnet wire. For 31-turn windings, cut two 40 inch (102 cm) lengths of magnet wire. Note that two

types of cores are supplied. The thicker core, E680025 is used for the 30 dB coupler and the thinner

core, E680008 is used for the 20 dB coupler.

 Using the photograph as a guide, wind the required number of turns onto the toroid cores. Make sure

that the direction of the winding is the same as in the photograph. Turns are counted by the number

of times the red enamel wire passes through the inside of the toroid. The photograph shows a 10-turn

inductor; the 31 turn inductor is identical except for the number of turns. The wire should be evenly

spaced around the core and will occupy about 90% of the core.

 Remove the enamel insulation from the ends of the wires. A hot soldering iron, can be used or

sandpaper can be used. When the insulation is removed, the ends of the wire should be tinned with a

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Summary of Contents

Page 1 - R e v B , J u n e 7 , 2 0 0 6

1ELECRAFT CP1 DUAL DIRECTIONAL COUPLERR e v B , J u n e 7 , 2 0 0 6The Elecraft CP1 is a dual directional coupler that provides high directivity, can

Page 2

2light coating of solder. The insulation should be removed to within about 1/8 inch (3.2mm) of thecore. Mount each inductor in its indicated position

Page 3 - Installation of Mounting Feet

3Completed CP1 (20 dB version shown)CP1 Schematic, rev. AToroid Wound With 10 turns.Installation of Mounting Feet

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Elecraft CP1 User Manual

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