OK, but my point is this: what aspects of the sum do you care about? Do you care if the result is a*x+b*y where x and y are your two signals and a,b are constants that are not exactly 1? If they are not exactly one, do you care more about the ratio a/b or simply that the result has roughly some particular total power and both signals are present? For example: if you have a point-to-point RF link and there are two transmitters (one at 100MHz and the other at 120MHz) and they share the same antenna, you don't really care if the two signals experience exactly the same gain and phase-shift, as long as neither of them is greatly attenuated or distorted. On the other hand, if you are doing an experiment where you are feeding two signals into a non-linear device and you expect to see sum and difference frequencies as well as higher-order products from the output, then you may care greatly about the _accuracy_ of the sum and the difference in the phase shift seen by the two signals. Sean On Wed, Oct 17, 2012 at 8:20 PM, Martin K wrote: > On Wed, Oct 17, 2012 at 3:11 PM, Sean Breheny wrote: >> Are you just looking to combine two signals together or are you >> looking for mathematical accuracy of the summed voltage? >> >> There are several different main combiner designs, some of which >> sacrifice overall amplitude for broad bandwidth, while others have >> almost no losses but only work over a narrow bandwidth. >> >> Sean > > My application is to add two signals, 100 MHz and 120 MHz. The power > is a few watts. > The generator is a DDS box and the load is an acousto-optic modulator. > > - > Martin K > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .