10MHz & 432MHZ Diplexer

I was in need for a 10 MHz and 432 MHz diplexer. Low power in order to feed a 10MHz signal on the same coax as the 432 MHz signal.

A quick search on the web returned sever designs, commercial as homebrew.

The one from HB9ABX was the one I wanted to try. It looked very simple and had filters for HF and 144/432 MHz. The design can be found on sever place on the internet. HERE

I steal the image from this website.

A lot of variable capacitors and I need two diplexers. I decided to use fixed capacitors instead and bend the inductors in shape. I didn’t need the lower branch L3&L4 because that would be for 145MHz.

C7 & C8 were replace by 47pF fixed ceramic capacitors

C1&C2&C3 were replaced by 4,7pF fixed ceramic capacitors.

Much to my surprise it worked instantly. No bending or pulling of the inductors needed. It worked right out of the box. Losses were very acceptable 0.2dB on 432 MHz and a bit more on 10 MHz. Isolation was very good.

See the pictures below:

The finished unit
The 10MHz bandpass
The 432MHz bandpass
The isolation between the 10MHz & 432MHZ ports
The finished unit