I don't know where this basic idea comes from - but I got the tip of this combiner from SM0IQC. Since the use of regular 2 to 1 combiners requires some more effort, I thougt this 4 to 1 combiner would be a nice compromise.  Why a compromise? Well, there are no free lunches!

 

By connecting everything together like the schematic below, the isolation between the different PA's is not near what it would be with set of 2 to 1 combiners. However, with todays LDMOS transistors the chance of a damaged PA is far less than with e.g. bipolars. Hence, I decided I'm willing to accept this compromise.

 

The semi-rigid parts are all 50 ohm and effective quater wave. Check the specification for the velocity factor of the coax in question and multiply the free space quater wave by the velocity factor. I ended up with 41mm on 1296MHz and 123mm on 432MHz. I allowed some space for the soldering connection and I did cut my coaxes 40mm and 122mm with about 0,5mm of isolation and 1mm center lead.

     

 

 

 

 

 

 

 

            

 

 

Quick simulation was made in Microwave Office - things do look so nice in theory! The design seemed fairly rigid even when some mismatch was applied. This was good enough for some practical tests on 432MHz (band choosen for practical measurement reasons). Below is the measurement for a set-up of one 1 to 4 plus one 4 to 1 combiner (see picture above).

     

 

 

 

 

 

 

 

 

Next step was to make combiners for 1296 that would fit into the compact design I was planning. Same test was made and very similar result to 432MHz was measured.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

SM6EAN  -  4 to 1 combiner

 

Updated 2008-10-18

First trial divider - 432MHz