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 good results.

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.

I can produce a limited number of the combiner for anyone interested, 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 can be sold for €500,- each plus shipping.

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 will have these installed 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 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 combiner 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 at my usual producer of mechanical parts).

The housing, top and bottom, is made of 6061 Aluminium, surface was "bead blasted". The striplines and contact pins were done in brass with "mirror polished" surface. The pictures below is exactly as the parts look 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. The 7/16 connectors are mounted using M3 stainless screws, top and bottom are assembled using M3 stainless screws.

Results

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.

The return loss can maybe be tuned a bit by adjust the spacing of the striplines a bit, I did not try this as 20 dB RL is good enough (same as a VSWR of 1:1.2). These tests were done without the three spacers.

Further tests will be done on the first produced device in the coming weeks.