23cm/1296 MHz high power 90 degree hybrid power combiner (by DJ9BV/SK)

30 years ago I built three copies of Rainers, DJ9BV (SK), 90 degree 23 cm hybrid combiner. The design was originally published in the DUBUS magazine (in 1994). Later on I got some modified dimensions for the coupler from Rainer, these seemed to work really well back then. Fast forward 30 years. I now have the need for some 23cm hybrid couplers again (for my new dish project). The ones I had back then are long gone (in the hands of another ham).

So I decided to try and redo the design from back them, this time using modern CAD and my usual "sub contractor" for milled aluminium and brass (same as I used for my 70cm hybrid combiners).

The original article in the excellent DUBUS magazine is copyrighted material, I got a written permission from Joachim ("Joe") Kraft CT1HZE to use and replicate the material on this page!

According to Joachim, I'm the only person (at all) that has permission to copy and publish the original article!

Original article from DUBUS magazine as a scanned PDF file (Thanks to Joachim/DUBUS!)

Drawing the combiner up in CAD from the dimensions was pretty straightforward and took less than 2 hours. The original design that I built had N connectors on all four ports, this time I wanted to use 7/16 connectors for higher power handling. The choice of connectors was easy, I designed around the same Radiall connectors I used in the 70cm combiner (Radiall order code R185403547).

After the design was done, I sent the design (STEP) files for manufacturing (2 x aluminium parts and 1 x stripline). The surface treatment on the two aluminium parts will be "bead blasted" and the brass stripline "mirror polished".

All production data are available here for download, using these you can have your own combiner produced.

I can also supply ready made and tested units, or complete kits (assembled by you), see below.

Production files

Screws needed:

16 pcs DIN 912 A4 Insex M3x10mm for 7/16 connectors
16 pcs DIN 912 A4 Insex M3x25mm for top/bottom aluminium parts
4 pcs DIN 912 A4 Insex M4x8mm for attaching bottom part to chassis (if needed)

Connectors needed:

4 pcs Radiall R185403547

Before assembly, remember to clean all threaded holes if needed. Sometimes you need to drive a tap into the holes to clear any chips still inside the holes from manufacturing.

I can produce a limited number of the combiner for anyone interested (or you can have your own made from the data linked above).

Completed combiners is sold for €410,- each plus shipping (approximately 1.5 Kg).

Should you be interested in assembling and testing it yourself, the price is €370,- plus shipping (all parts, screws, 7/16 connectors are in the kit, only thing not included is the "Jig")

My original DJ9BV combiners from 30 years ago (1995). Was used for combining multiple 2C39 water cooled cavities on 23 cm for EME, first on my 5 meter dish and later on my 8 meter dish.

CAD model and design

I designed the combiner in Autodesk Inventor. The internal dimensions of the enclosure and the stripline was taken from the original drawings in DUBUS magazine (including updated drawings of the stripline from Rainer DJ9BV (SK)).

The connectors used in the original design was N connectors. I wanted to use 7/16 connectors instead. I chose the same as in my 70 cm combiner from Radiall (order code R185403547). These connectors are not cheap, but quality looks superb.

The center pin on these connectors ends up in a 7 mm diameter "cup" on the back with a 3 mm hole. In order to make it easy to "interface" the stripline to these, I made small protrusions on the stripline that would fit into the "cups" and be soldered in place. I also made the stripline 2 mm thick instead of the original 1 mm, the housing was modified for the added thickness, basically to maintain the defined 9.5 mm air between housing top/bottom and the stripline.

The walls of the milled aluminium box are 5 mm thick, this enables me to use M3 screws for holding the two parts of the housing together. However, this raises a small problem. The 7 mm diameter "cup" of the 7/16 connectors needs a clearance of 16 mm around it to match 50 ohm, As the "cup" does not extend all the way thru the 5 mm thick walls, there is a couple of mm from the end of the cup to the stripline where the impedance is not 50 ohm.

Testing will show if this a problem (my best guess it is not too important). Should it be a problem, an easy fix is to mount a "collar" of 7 mm in diameter and 2 mm long, around the "pin" from the stripline just where it enters the "cup" of the 7/16 connector, effectively extending the "cup" all the way thru the 16 mm opening in the wall.

Jig for mounting the stripline

I made a small "jig" that will help with aligning the stripline, both in "X" direction and the height above the bottom. The stripline is designed so there should be 9.5 mm air above and below the stripline. Using four jigs, you can place the stripline accurately (note, the jig is NOT supplied in the "assemble yourself kit" !

The two jigs that are placed at the same wall as the connectors will make sure the stripline has the same distance to the wall on both the left and right side. All four jigs will also make sure the stripline is placed exactly 9.5 mm above the "floor" of the housing.

The file for the jig is available at the top of this page together with the rest of the design.

The first prototype from production

Parts for the prototype arrived. Everything was as expected, quality as usual very good from the "milling house" I use.

The housing, top and bottom, are both made of 6061 Aluminium, surface was "bead blasted" (don't use anodized!). The stripline are done in brass with "mirror polished" surface. The pictures below is exactly as the parts looked from production, the only thing I did to the brass, was to remove the thin oil the stripline was stored in (in a plastic bag).

Stripline is soldered to the 7/16 connectors (using a high wattage soldering iron and some flux). The 7/16 connectors are mounted using M3 stainless screws (DIN 912 A4, Insex, M3 x 10mm), top and bottom are assembled using M3 stainless screws (DIN 912 A4, Insex, M3 x 25mm).