(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.

        Possible uses.

A directional coupler with HF-output can be used to measure the match of filters. Conveniently using only microwatt-power, from a simple signal generator. A powerful generator is not needed to measure filters (see "Band pass filters for 145MHz").

It also showed to be ideal in use for sensitivity measurements on our Rotterdam repeaters, which were working in full duplex mode on a dummy load or an antenna. The coupler was inserted between the antenna and the duplex filter, with the signal generator connected to the "return" port, via variable 50 Ohms attenuators. 

Tests on the older prototype directional couplers with HF-output, clearly showed differences in reflection damping, between different types of low power 50/51 ohms terminating resistors and dummy loads. Good terminators showed over 20dB return loss.

          Technical data.
These directional couplers have 20mm log coupling tracks. At the 90 degr. track corners, the outsides of the tracks are angled at 45 degr. to prevent reflections ban into the track. The 45 degr sides should act as mirrors, reflecting waves in the 90degr. direction.

The measured coupling loss at 145 MHz is ca. 32 dB.
This value ensures negligible influence from the output ports to the impedance of the 50 Ohms thru-line, or generating IMD, and less chance of damage to connected signal generators, due to high power output. 

At 435 MHz the measured coupling loss is abt. 23 dB. 

At 29 MHz the measured coupling loss is abt 46 dB.

At still lower frequencies the coupling loss rises with 6 dB / oktave, Making it to insensitive for most uses. But it could act as a very good 64dB attenuator on 3.5 MHz. Suitable for monitoring a transmitter output.

The new developed PCB versions with DC output use modern SMD Skottky diodes with very low signal threshold, and 50 Ohms 2W (or 2x 100Ohm 1W in parallel) SMD terminating resistors. This indicates a maximal continues power handling of abt. 1500 W (not tested). The DC outputs have an internal resistance of abt. 100 kOhms. 

When the FWD or REFL DC outputs are loaded with a hi-Z digital DC meter (>= 10 Mohm), and the main line is connected to a source of 1W @ 145 MHz, a highZ meter should indicate at least 100mV DC output. With 800W input 9.4Vdc output could be expected.

        New PCB versions.
The old 2003 versions of 200DPI DIY PCB masks were drawn with a drawing program, so no Gerber files of them exist.
The PCB top copper drawings of these old designs are plublished HERE.

To be able to order professional PCBs, i designed new versions, using PCB design software "FREEPCB", They have the same track dimensions, but newer type SMD components,  

One small PCB with DC output, but without BNC busses, enables installment inside equipment, connect by on-soldered coax cables.

        Connections.
I advise you to use PTFE (Teflon (R)) insulated BNC busses. They can withstand temperatures up to 400C, so you can solder their rim directly onto the steel housing, without damaging the position of their central pins. To be sure, place a PTFE BNC plug on the bus before soldering.

Use two long ground lugs at each BNC, to connect them to the "ground" surfaces of the PCBs.

The whole PCB should make NO electrical contact to the steel housing, exept at the BNC busses.