High isolation RF combiner for HF

[merseyless]

Hi All,

I've been beating my head against a image rejection mixer that just won't cooperate.
I think the problem might be with the 10.7MHz lumped element quadrature coupler that I made which goes to the IF circuitry. I plan on adjusting the topology to place a prefabbed quadrature coupler on the RF input and use a high isolation RF combiner on the output of the two mixers.

At the moment, I'm considering an opamp based solution. two opamps acting as buffers and a third as a summing amplifier. While it could work, the signal I'm looking at may still be at -30dBm. It shouldn't be a problem but I've never fed a signal that weak into an opamp. I'm also concerned that there would be an unwanted increase in noise from all those active components.

Are there any other designs that I should consider?

[DimitriP]

You might want to show the design, the frequencies involved and in what way it refuses to cooperate.
As for alternatives, from minicircuits to Analog Devices to another discrete contraption there are a few ....