Carsten Groen's (OZ9AAR) personal place

70cm/432 MHz high power 90 degree hybrid powercombiner

I got the dimensions for a 70cm hybrid combiner from Frank NC1I. The design was done by Fred K1FMS.

Both Frank NC1I, and Peter PA2V, has this combiner running with very good results.

I also made a 23 cm combiner based on DJ9BV (SK) design.

Drawing the combiner up in CAD from the supplied dimensions was pretty straightforward, finding suitable connectors was a bit more work. I wanted to use DIN 7/16 connectors on all ports as N type connectors is, at best, marginal at higher power levels at 70 cm.

After the design was done, I had a prototype produced from the CAD model. The measurements done on the first prototype was not done with the Rexolite spacers between the two striplines. The next combiners produced will have these included as well.

All production data are available here for download (by permission of Frank NC1I and Fred K1FMS), using these you can have your own combiner produced.

Production files:

The ZIP file linked below contains a number of 3D STEP files:

1. 1 pcs "Body.stp" - The lower part of the housing, milled aluminum
2. 1 pcs "Top.stp" - The upper part of the housing, milled aluminum
3. 2 pcs "Stripline.stp" - The stripline, milled and mirror polished brass
4. 2 pcs "Spacer2.stp" - This is the large spacers between top/bottom and striplines, milled Rexolite
5. 1 pcs "Spacer.stp" - This is the small spacer between the stiplines, you need one, milled Rexolite
6. 4 pcs "Contact pin" - This is the "contact pin" for connecting striplines to the 7/16 connectors, milled and mirror polished brass

The ZIP file also contains three PNG (image) files:

1. "Body threads.png" - Details of threads on the lower housing
2. "Top threads.png" - Details of threads on the upper housing
3. "Contact pin threads.png" - Details of threads on the four contact pins
   

You can download the ZIP file here.

Screws needed:

1. 16 pcs DIN 912 A4 Insex M3x10mm for 7/16 connectors
2. 10 pcs DIN 912 A4 Insex M3x35mm for top/bottom aluminium parts
3. 8 pcs DIN 963 Brass screws M2.5x8mm for contact pins/striplines
4. 4 pcs DIN 912 A4 Insex M4x8mm for attaching bottom part to chassis (if needed)

Connectors needed:

1. 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), the combiner is NOT cheap, the raw material price (milling time) is high, and the used 7/16 connectors are also not cheap!

Completed combiners is sold for €500,- each plus shipping (approximately 1.5 Kg).

Should you be interested in assembling and testing it yourself, the price is €440,- plus shipping (all parts, screws, 7/16 connectors are in the kit)

CAD model and design

I designed the combiner in Autodesk Inventor. The different parts (housing, stripline and partly the "connector pins") were based on the original measurements from Frank NC1I and Fred K1FMS work.

I had to change the connector pins that connects the stripline to the 7/16 connectors a bit as well as the housing (to keep 50 ohm at connector center pin).

I was able to find some nice 7/16 female connectors from Radiall (order code R185403547), although not exactly cheap, they are great and fits this design perfectly. The center pin ends up in a 7mm diameter "cup" on the back, easy to interface to the stripline using a brass "contact pin" that was soldered in place in the connectors.

In the center of the striplines and in the top and bottom covers there are milled circular pockets. These pockets holds three spacers made of "Rexolite". The preliminary tests had not these included but production units (and kits) will have these installed/included for added stability.

Below are two screenshots of the completed combiner, the one to the right shows the combiner from the bottom. There are four M4 threaded holes (4 pcs DIN 912 A4, insex, M4 x 8mm included in readymade combiners/kits) for mounting it to a chassis if needed. The combiner is quite heavy due to the construction, the total weight with connectors etc is 1.5 Kg.

The first prototype from production

After waiting a couple of weeks, the parts for the first combiner arrived. All seemed to have been made 100% to specification (not surprised as it was done by my usual producer of mechanical parts).

The housing, top and bottom, are made of 6061 Aluminium, surface was "bead blasted" (don't use anodized!). The striplines and contact pins were 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 parts, was to remove the thin oil they were stored in (in individual plastic bags).
Striplines was attached to the contact pins using M2.5 brass screws (DIN 963 brass, M2.5 x 8mm). 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 35mm).

(The striplines have been optimized a bit for even better return loss and isolation in the finalized design).

Preliminary tests

I did some preliminary tests of the combiner. The return loss is better than 20 dB (more like 22 dB) on all ports. Phase difference is below 0.2 degrees. These tests were done without the three spacers.

After the prototype was measured, Fred K1FMS did some small optimization of the striplines, this improved the return loss and isolation with a few dB's!

Further tests will soon be done on the first produced devices (with optimized stripline!).