A Range of Dual Directional Couplers For VHF / UHF

This range of dual directional couplers was designed using Microwave Office to be used with the " Pic Based Power meter " and other test gear . The coupling factor was designed to allow the power meter to read up to 100 Watts as per the " Tap" attenuator described in the ARRL handbook ie about 40dB , the couplers were then optimised for each of the VHF / UHF amateur radio bands ( 2m , 70cm & 23cm ) they have been designed to fit in to a " standardised " housing to keep manufacturing costs down . The housing is machined from an Aluminium block to ensure rugged & reliable performance for many years use.

145 MHz 40dB Dual Coupler

The Schematic of the Dual coupler as modelled with Microwave Office

Schematic of 145MHz Dual Coupler

The frequency response of the Dual coupler as modelled in Microwave Office

Frequecy Respose of 145MHz Dual Coupler

The completed artwork from Microwave Office

PCB Artwork as Exported from Microwave Office

Plot of the Coupler

435 MHz 40 dB Coupler

The Schematic of the Dual coupler as modelled with Microwave Office

Schematic Circuit of the 435 MHz dual coupler as modelled using Microwave Office

The frequency response of the Dual coupler as modelled in Microwave Office

Graph of Frequency Response for the 435 MHz Dual Coupler

The completed artwork from Microwave Office

The Artwork for the 435MHz Duyal coupler as output from Microwave Office

1296 MHz 40dB Coupler

The Schematic of the Dual coupler as modelled with Microwave Office

Schematic of 1296MHz Dual Coupler

The frequency response of the Dual coupler as modelled in Microwave Office

Frequency Response of 1296 MHz Dual Coupler

The completed artwork from Microwave Office

Artwork from Microwave office

Mirrored Artwork for both 145 MHz Coupler , 435MHz Coupler & 1296 MHz Coupler

435MHz 40dB Coupler Artwork

The Dual coupler housings are detailed below

The General Assembly Drawing , housing & cover drawings are common to 145 & 435MHz frequency variants, only the PCB is changed to suit each band variant however the 1296 MHz version the line length was becoming a significant part of the wave length so a shorter box is required to go with the shorter coupled line lengths.

General Assembly Drawing for the Dual Coupler

The Coupler body ( Low frequency variant )

The Dual Directional Coupler Body

The Coupler cover (Low frequency variant )

Dual Coupler Cover

View of the completed 145MHz Dual Coupler

{short description of image}View of completed Dual Directional coupler

The frequency response of the coupler as plotted using an FSH3 spectrum analyser

Response plotted using an FSH3 Spectrum Analyser

The parts listing for ALL coupler variants only one PCB is used per coupler

Item Manufacturer Part No. Supplier Supplier's Part No QTY

PCB

 Homemade 145MHz Dual Coupler Homemade  To suit band Chosen 1

 

 Homemade 435 MHz Dual Coupler Homemade To suit band Chosen 1

 

 Homemade 1296MHz Dual Coupler Homemade To suit band Chosen 1

Housing

 Homemade   Homemade   1

Cover

 Homemade   Homemade   1

100R "0805" 

Various

        4

SMA Socket

 Various   FEC

 105 - 6376

4

M2.0 x 6 mm " A2"

 Various  

FEC

  142 - 0028 22

M2.5 x 6 mm "A2"

 Various   FEC  142 - 0030 12

M2.0 Crinkle " A2"

 Various   FEC  161 - 4000 6

FEC is

Farnell Electronic Components      

After making these couplers I found their directivity to be poor only about 10 - 12 db , not much use if you are trying to measure return losses greater than15 dB so a redesign in the light of experience will follow shortly these will use STRIPLINE techniques not Microstrip , the reason for the lack of directivity being due to the inherent differential speeds of propagation on the transmission & coupled lines caused by the different dieletric above & below the transmission lines .

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This page last updated 17/03/2014