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Pa0nhc directional couplers.
MASKS for home made double sided PCBs.
199909 / 2013 / 20171229

(C) The use, copy and modification of all info on this site is only permitted for non-commercial purposes, and
thereby explicitly mentioning my radio amateur call sign "pa0nhc" as the original writer / designer / photographer / publisher.

DIY masks for directional couplers with DC and RF output.

Directional couplers with RF-output.
For measuring return losses using very low power.
Shown are PCB's for different connectors and casings.

BNC receptacles are of screw-nut-type with PTFE (Teflon (R))  dielectric. 

Casings used are TEKO type 371 or 372.

N receptacles are of flat flange-type with PTFE dielectric.

PTFE insulation enables soldering of the outside of the bus to the PCB and/or steel enclosure, due to the high melting temperature of the material.

The flanges of N busses are soldered onto the copper bottom lane of the PCB.

Solder the  the mass-connections of the PCB to the nuts of the BNC receptacles
not to the box itself.

All  PCB tracks are soldered directly under the center-pins of all BNC's.
Before installing the BNC busses, lay the PCB into the enclosure FIRST.

The "50 ohms" terminating resistors comprises each of 3 SMD resistors 150 ohms in parallel. 

IMPORTANT: The back plane is full copper.
The little holes must be filled with copper rivets or pieces of thick wire, and then soldered on both sides of the PCB
These are interconnections between mass planes on both sides of the PCB.

Reverse the diodes if negative DC output is wanted.

There are NO Gerber files for the following masks.
They were simply drawn using Paint Shop Pro in 1999.
Open the PDF versions in Adobe Reader, and print them in size "100%".

RF currenst should flow through the back plane of the PCB, NOT through the metal screening of the box.
Leave the PCB free from the box.

The PCB mass planes must ONLY be soldered to the nuts or thread of the connectors.
The mass connections to be soldered, are marked with a "ground" sign.
The signal tracks (RF and DC) are soldered directly under the center-pins of connectors.

 

PCB 78mmx44mm, BNC receptacles on sides.
Download this mask as PDF.

 


PCB 48x44mm, with BNC receptacles on two sides,
and two N receptacles screwed to the outside of the back.
Per N receptacle, use two short screws with their heads inside.
Further use two longer screws with the heads outside.
Then place inside on each some nuts as spacer.
Fix the PCB to the long screws with a nut and a teeth washer.
Then install the BNC's and solder the PCB to all receptacles.
Download this mask as PDF.

 

Universal PCB 48x44mm, BNC receptacles on all sides,
or N-receptacles on the on the back.

Download this mask as PDF.

 


Directional couplers with DC-output.
For use in SWR / power meters.
Read also the instructions above about mass connection.

      The components for DC output :
The RF-filters in the DC-outputs are SMD-components :
    - At the diode (BAT85) : 100pF to mass,
    - From diode to output 150 ohms ,
    - Output connections "X" are bridged with 10nF.

X= The DC output connection to
    - BNC receptacles   or
    - Feed-through-Cs and external screened wires.


Parts locations

Parts locations for DCout couplers.
Left to rigth : BNCpin, filterR (= 150 Ohms or higher), filterC=100p
The "50 ohms" terminating resistors comprises each of 3 SMD resistors 150 ohms,
soldered on top of each other (in parallel). 

 

PCB 48x44mm, BNC receptacles on sides.
Download this mask as PDF.

 

PCB 48x44mm, BNC receptacles on sides.
Download this mask as PDF.

 

PCB 48x44mm, with BNC receptacles on two sides for DC output,
and two N receptacles for RF screwed to the outside of the back.
Per N receptacle, use two short screws with their heads inside.
Further use two longer screws with heads outside,
and place inside each some nuts as spacer.
Fix the PCB to the long screws with a nut and a teeth washer
Then install the BNC's and solder the PCB to all receptacles.

Download this mask as PDF.

 

Universal PCB 48x44mm, BNC receptacles on all sides, or N- receptacles on the back.
Download this mask as PDF.

 


Pictures of prototypes:

Directional coupler with HF-output, -30.5dB at 145 MHz, -20 dB at 435 MHz.
This unit is very useful for weak coupling of HF-sources,
and return loss measurements with very low, to high power.
The housing is a TEKO 371 box.
Directional coupler with detectors and DC-output in a TEKO 371 enclosure.
This unit can be used as power meter and SWR meter for 28MHz to 435MHz.
A/B port 25W 2,5W 0,25W

145MHz:

(V) (V) (V)
A fwd. 1,91 0,520 0,070
B fwd. 1,90 0,52 0,065
A refl. 0,039 0,0038 0,0001

435MHz:

     
A fwd. 5,28 1,475 0,33
B refl. 0,300 0,0485 0,0043
A refl. 0,361 0,057 0,005

 

Directional coupler PCB with detectors and DC-output.
Replacing the very poor detector circuit in a cheap citizens band "power/SWR meter".

It now can be used to measure on 28MHz, 145MHz and 435MHz.
Sensitivity of the SWR-metering is: 145MHz/5W, 435MHz/1W.
Full Scale Deflection for power measurements was adjusted to 10W.
Read remarks below.

As shown here, a simple but accurate PCB works, with receptacles soldered on the mass side (back), screwed to the housing.
"Forward" and "Reflected" DC outputs are connected to separate meters.
A switch is used to calibrate the "Forward" meter for full scale deflection on 145MHz or 435MHz when used as a power meter.
When used as an SWR meter, the double potentiometer adjusts the forward meter for Full Scale Deflection.

To prevent HF radiation, a better solution is to put the PCB in a dedicated, RF-tight box.
The DC-outputs should be RF filtered before they are connected to the outside if this box, and to the meters. 

REM: do NOT leave these instruments connected during daily use, as the diodes will inject some distortion to the power line.
Causing radiation of harmonics.