Directional Coupler(s)

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This page last updated 07/17/2019

If you are interested in the theory, you want Michael Ellis's page and his software mentioned below,
you will find that the pages have been revised from my original design.
The links below along with the spreadsheets will allow you to have the complete design information.
Note: the software was written in VB3 and requires a 32 bit OS like XP
[You knew there was a good reason to keep that old box !] or in PDF format

Description of software:


Actual Software

Note: for some reason the link above does not yield a download but an error about not available.

Copy the link and past into the URL line on your browser and the download works !


Some Supplementary spreadsheets that I used

Coupler Loss Tables.xls

Power levels at input and ports on Directional Couplers.xls


If all you want is a simple circuit, Kits & Parts still sells their kit SWR Bridge Kit



Alex Directional Coupler for Hermes-Lite 2 and other applications

The Circuit below provides a buffered low impedance output
that is compatible with software that is used with openHPSDR
hardware and Hermes-Lite 2.  The board can also be used stand alone
with meters on the outputs or with an Arduino and your own display system.

See below for analysis file and spreadsheet


Alex Directional Coupler for HL2 - Others



Documentation Alex Directional Coupler HL2 Others.pdf

Gerbers Alex Dir Cplr 4 HL2


Link to OSH Park - 3@ $9.45


Analysis of the Alex power sensing circuit and expected output vs input power

Theoretical Analysis of the openHPSDR ALEX Power Sense Circuit.pdf

and the spreadsheet for the calculations

Perfect Theoretical analysis of Alex Directional Coupler.xls



New Directional Coupler For Test, Watt meter, Pure Signal etc.


This is a revised version of the original design below using SMT parts.

The circuit below assumes a 100 Watt transmitter and the use of the Dual AD8307 board

found on my RF_Power_Meter page to make a SWR Power meter.



Documentation New Directional Coupler.pdf

Gerbers New_DC_


Link to OSH Park - 3@ $6.80




Low Power Directional Coupler

This was made to work with my dual AD8307 board or an AD8302 Module like this ebay part.

The Dual AD8307 info can be found on my RF_Power_Meter page.



Schematic Directional Coupler and Detector.pdf

Gerbers AA Directional There are no OSH Park link for this board.


Original Directional Coupler Design


I originally up this board to be a piece of test equipment to be used with the

RF_Power_Meter, but it is also useable for Pure Signal

Later found out it is very similar to the Elcraft CP-1 Coupler.

If you are interested in the theory you want Michael Ellis's page and his Excel spreadsheet

Note that the turns ratios are independent of power levels.

The core size, spacing and insulation determine the max power level.

For higher power a larger PCB and cores would be necessary.



Schematic: Directional Coupler.pdf
BOM:  RF Coupler BOM.pdf
Gerbers: Directional

Link to OSH Park:

NOTE:  The link to OSH Park also allow ordering PCBs